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A Critical Review of Nanoparticles as Potential Agents for Enhancing Oil Recovery
Farad Sagala, Tatiana Montoya, Nashaat N. Nassar
Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
GRAPHICALABSTRACT

Abstract: Nanoparticles have become enormously attractive materials for improving oil recovery at laboratory and field scales. Because of their nanosize, they can move freely in the porous media and can interact more easily with the reservoir fluids. This is an advantage in contrast with the conventional and most commonly used chemicals, such as polymers, alkaline and surfactants, whose sizes are larger, and thus increasing the possibility to be adsorbed on the rock surfaces, which has a negative impact on their efficiencies. In oil recovery enhancement processes, nanoparticles are used as either nanofluids, nano-emulsions or nano-catalysts. In either way, various mechanisms result that can significantly reduce the residual oil saturation, which can extend the productivity of mature fields. Recently, the role of nanoparticles in enhancing oil recovery has been extensively reported. Therefore, this review paper summarizes some of the critical evidence of the major types of nanomaterials commonly used in EOR. It addresses how nanofluids are stabilized and dispersed as tertiary agents in the reservoirs, and thus contribute to additional oil recovery. Also, a summary of the common parameters, mechanisms that control nanoparticle oil recovery, brief environmental concerns of using nanoparticles. Lastly, a discussion of the present opportunities and challenges associated with the use of nanomaterials is reviewed.

Keywords: Enhanced oil recovery, Nanoparticle, Nanotechnology, wettability, Nanofluids
Table of Contents
TOC o “1-3″ h z u 1. Introduction PAGEREF _Toc518488205 h 22. Types of nanoparticles commonly used in enhancing oil recovery PAGEREF _Toc518488206 h 63. Nanoparticle stabilization for EOR application PAGEREF _Toc518488207 h 144. Mechanisms of enhancing oil recovery using nanoparticles PAGEREF _Toc518488208 h 165. Effect of various factors on nanoparticle performance PAGEREF _Toc518488209 h 346. Concerns about the use of nanotechnology in enhancing oil recovery PAGEREF _Toc518488210 h 427. Opportunities and challenges PAGEREF _Toc518488211 h 428. Conclusions and future outlook PAGEREF _Toc518488212 h 42References PAGEREF _Toc518488213 h 43
1. Introduction
World conventional oil recovery methods, best known as primary and secondary methods, typically extract approximately one-third of the original oil-in-place in the reservoir. Estimated reserves worldwide range up to 1.5 trillion barrels ADDIN EN.CITE <EndNote><Cite><Author>Abas</Author><Year>2015</Year><RecNum>89</RecNum><DisplayText>1</DisplayText><record><rec-number>89</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525418999″>89</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Abas, N</author><author>Kalair, A</author><author>Khan, N</author></authors></contributors><titles><title>Review of fossil fuels and future energy technologies</title><secondary-title>Futures</secondary-title></titles><periodical><full-title>Futures</full-title></periodical><pages>31-49</pages><volume>69</volume><dates><year>2015</year></dates><isbn>0016-3287</isbn><urls></urls></record></Cite></EndNote>1. Thus, it is estimated that the remaining oil as a residual oil after conventional recovery methods would be approximately 1.0 trillion barrels ADDIN EN.CITE <EndNote><Cite><Author>Council</Author><Year>1976</Year><RecNum>88</RecNum><DisplayText>2</DisplayText><record><rec-number>88</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>88</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Council, NP</author></authors></contributors><titles><title>Enhanced oil recovery–an analysis of the potential for enhanced oil recovery from known fields in the United States–1976–2000</title><secondary-title>Washington, DC</secondary-title></titles><periodical><full-title>Washington, DC</full-title></periodical><dates><year>1976</year></dates><urls></urls></record></Cite></EndNote>2. Several enhanced oil recovery (EOR) techniques generally grouped together as tertiary production schemes have targeted these huge unexploited reserves PEVuZE5vdGU+PENpdGU+PEF1dGhvcj5CaWxhazwvQXV0aG9yPjxZZWFyPjIwMDY8L1llYXI+PFJl
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ADDIN EN.CITE.DATA 3-7. However, finding a low cost and effective method to extract this remaining residual oil after primary and secondary recovery remains a challenge, given that the current tertiary practices depend on crude prices ADDIN EN.CITE <EndNote><Cite><Author>Maggio</Author><Year>2009</Year><RecNum>94</RecNum><DisplayText>8, 9</DisplayText><record><rec-number>94</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>94</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Maggio, Gaetano</author><author>Cacciola, Gaetano</author></authors></contributors><titles><title>A variant of the Hubbert curve for world oil production forecasts</title><secondary-title>Energy Policy</secondary-title></titles><periodical><full-title>Energy Policy</full-title></periodical><pages>4761-4770</pages><volume>37</volume><number>11</number><dates><year>2009</year></dates><isbn>0301-4215</isbn><urls></urls></record></Cite><Cite><Author>Kong</Author><Year>2010</Year><RecNum>91</RecNum><record><rec-number>91</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525933841″>91</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Kong, Xiangling</author><author>Ohadi, Michael</author></authors></contributors><titles><title>Applications of micro and nano technologies in the oil and gas industry-overview of the recent progress</title><secondary-title>Abu Dhabi international petroleum exhibition and conference</secondary-title></titles><dates><year>2010</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1555633153</isbn><urls></urls></record></Cite></EndNote>8, 9. Hence, a search is needed for sustainable, cost-effective, efficient, and environmentally friendly techniques.
Generally, enhanced oil recovery techniques consist of various mechanisms including oil-water interfacial tension reduction ADDIN EN.CITE <EndNote><Cite><Author>Shah</Author><Year>2012</Year><RecNum>248</RecNum><DisplayText>10</DisplayText><record><rec-number>248</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>248</key></foreign-keys><ref-type name=”Book”>6</ref-type><contributors><authors><author>Shah, Dinesh Ochhavlal</author></authors></contributors><titles><title>Improved oil recovery by surfactant and polymer flooding</title></titles><dates><year>2012</year></dates><publisher>Elsevier</publisher><isbn>0323141579</isbn><urls></urls></record></Cite></EndNote>10, wettability alteration ADDIN EN.CITE <EndNote><Cite><Author>Abe</Author><Year>2005</Year><RecNum>124</RecNum><DisplayText>11</DisplayText><record><rec-number>124</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>124</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Abe, Ayodeji Adebola</author></authors></contributors><titles><title>Relative permeability and wettability implications of dilute surfactants at reservoir conditions</title></titles><dates><year>2005</year></dates><urls></urls></record></Cite></EndNote>11, and fluid viscosity enhancement ADDIN EN.CITE <EndNote><Cite><Author>Shu</Author><Year>1986</Year><RecNum>126</RecNum><DisplayText>12</DisplayText><record><rec-number>126</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>126</key></foreign-keys><ref-type name=”Generic”>13</ref-type><contributors><authors><author>Shu, Winston R</author><author>Hartman, Kathy J</author></authors></contributors><titles><title>Thermal recovery method for viscous oil</title></titles><dates><year>1986</year></dates><publisher>Google Patents</publisher><urls></urls></record></Cite></EndNote>12. These mechanisms are achieved using the common EOR techniques such as chemical, miscible and immiscible gas or liquid flooding, and thermal methods. To design an EOR technique, the aim is to achieve any of the aforementioned mechanisms. A successful design must also be economical, efficient and reliable, yet most of the current methods are technically successful but economical failures, thus creating a gap for venturing into more alternative techniques to recover the residual oil in a cost-effective and efficient way.

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ADDIN EN.CITE.DATA 18-24. The diversification in their uses is due to their unique size and shape that alters their chemical and physical properties in comparison to their bulk counterparts ADDIN EN.CITE <EndNote><Cite><Author>Kong</Author><Year>2010</Year><RecNum>91</RecNum><DisplayText>9</DisplayText><record><rec-number>91</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525933841″>91</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Kong, Xiangling</author><author>Ohadi, Michael</author></authors></contributors><titles><title>Applications of micro and nano technologies in the oil and gas industry-overview of the recent progress</title><secondary-title>Abu Dhabi international petroleum exhibition and conference</secondary-title></titles><dates><year>2010</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1555633153</isbn><urls></urls></record></Cite></EndNote>9. In bulk materials, the number of atoms at the surface is significantly smaller than in the whole bulk material, which makes their chemical and physical properties constant regardless of their size ADDIN EN.CITE <EndNote><Cite><Author>Kong</Author><Year>2010</Year><RecNum>91</RecNum><DisplayText>9</DisplayText><record><rec-number>91</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525933841″>91</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Kong, Xiangling</author><author>Ohadi, Michael</author></authors></contributors><titles><title>Applications of micro and nano technologies in the oil and gas industry-overview of the recent progress</title><secondary-title>Abu Dhabi international petroleum exhibition and conference</secondary-title></titles><dates><year>2010</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1555633153</isbn><urls></urls></record></Cite></EndNote>9. However, when the size is reduced, several properties such as quantum confinement, i.e., optical and electronic properties, magnetism, thermal resistance, catalytic activities, internal pressure, melting point, dispersion ability and intrinsic reactivity are all altered ADDIN EN.CITE <EndNote><Cite><Author>Perez</Author><Year>2007</Year><RecNum>81</RecNum><DisplayText>25</DisplayText><record><rec-number>81</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>81</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Perez, J Manuel</author></authors></contributors><titles><title>Iron oxide nanoparticles: Hidden talent</title><secondary-title>Nature Nanotechnology</secondary-title></titles><periodical><full-title>Nature Nanotechnology</full-title></periodical><pages>535-536</pages><volume>2</volume><number>9</number><dates><year>2007</year></dates><isbn>1748-3387</isbn><urls></urls></record></Cite></EndNote>25. This is due to the surface area to volume ratio that becomes larger, and hence the number of atoms at the surface becomes significant, more atoms are exposed to the surface of the material compared to the atoms in the bulk material thus increasing the surface energy ADDIN EN.CITE <EndNote><Cite><Author>Lei</Author><Year>2010</Year><RecNum>82</RecNum><DisplayText>26</DisplayText><record><rec-number>82</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>82</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Lei, Y</author><author>Mehmood, Faisal</author><author>Lee, Sungsik</author><author>Greeley, J</author><author>Lee, Byeongdu</author><author>Seifert, Soenke</author><author>Winans, Randall E</author><author>Elam, Jeffrey W</author><author>Meyer, Randall J</author><author>Redfern, Paul C</author></authors></contributors><titles><title>Increased silver activity for direct propylene epoxidation via subnanometer size effects</title><secondary-title>Science</secondary-title></titles><periodical><full-title>Science</full-title></periodical><pages>224-228</pages><volume>328</volume><number>5975</number><dates><year>2010</year></dates><isbn>0036-8075</isbn><urls></urls></record></Cite></EndNote>26. Therefore, nanoparticles present favourable characteristics, their active surface sites can be utilized in various ways and for this reason, doors for research have been opened using these properties for oil and gas related applications ADDIN EN.CITE <EndNote><Cite><Author>Ogolo</Author><Year>2012</Year><RecNum>92</RecNum><DisplayText>15</DisplayText><record><rec-number>92</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525934204″>92</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Ogolo, NA</author><author>Olafuyi, OA</author><author>Onyekonwu, MO</author></authors></contributors><titles><title>Enhanced oil recovery using nanoparticles</title><secondary-title>SPE Saudi Arabia section technical symposium and exhibition</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613992300</isbn><urls></urls></record></Cite></EndNote>15.

In addition, nanotechnology not only offers environmental and cost-effective industrial processes but also offers precise manipulation of atoms and molecules allowing the control of their properties ADDIN EN.CITE <EndNote><Cite><Author>Serrano</Author><Year>2009</Year><RecNum>204</RecNum><DisplayText>24</DisplayText><record><rec-number>204</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>204</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Serrano, Elena</author><author>Rus, Guillermo</author><author>Garcia-Martinez, Javier</author></authors></contributors><titles><title>Nanotechnology for sustainable energy</title><secondary-title>Renewable and Sustainable Energy Reviews</secondary-title></titles><periodical><full-title>Renewable and Sustainable Energy Reviews</full-title></periodical><pages>2373-2384</pages><volume>13</volume><number>9</number><dates><year>2009</year></dates><isbn>1364-0321</isbn><urls></urls></record></Cite></EndNote>24. Therefore, the rapid advancement in nanotechnology in the past few decades has led to the application of various nano-sized materials in the oil and gas industry, in the fields of exploration, drilling, production and post-production activities ADDIN EN.CITE <EndNote><Cite><Author>Matteo</Author><Year>2012</Year><RecNum>80</RecNum><DisplayText>27, 28</DisplayText><record><rec-number>80</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>80</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Matteo, Cocuzza</author><author>Candido, Pirri</author><author>Vera, Rocca</author><author>Francesca, Verga</author></authors></contributors><titles><title>Current and future nanotech applications in the oil industry</title><secondary-title>American Journal of Applied Sciences</secondary-title></titles><periodical><full-title>American Journal of Applied Sciences</full-title></periodical><pages>784</pages><volume>9</volume><number>6</number><dates><year>2012</year></dates><isbn>1546-9239</isbn><urls></urls></record></Cite><Cite><Author>Khalil</Author><Year>2017</Year><RecNum>71</RecNum><record><rec-number>71</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>71</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Khalil, Munawar</author><author>Jan, Badrul Mohamed</author><author>Tong, Chong Wen</author><author>Berawi, Mohammed Ali</author></authors></contributors><titles><title>Advanced nanomaterials in oil and gas industry: Design, application and challenges</title><secondary-title>Applied Energy</secondary-title></titles><periodical><full-title>Applied Energy</full-title></periodical><pages>287-310</pages><volume>191</volume><dates><year>2017</year></dates><isbn>0306-2619</isbn><urls></urls></record></Cite></EndNote>27, 28. This is due to the increase of the global demand for energy caused by the population growth, and the challenges with the currently used conventional methods, which has forced researchers to explore the mechanisms and applicability of the nanomaterials in extracting more hydrocarbons ADDIN EN.CITE <EndNote><Cite><Author>Khalil</Author><Year>2017</Year><RecNum>71</RecNum><DisplayText>28</DisplayText><record><rec-number>71</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>71</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Khalil, Munawar</author><author>Jan, Badrul Mohamed</author><author>Tong, Chong Wen</author><author>Berawi, Mohammed Ali</author></authors></contributors><titles><title>Advanced nanomaterials in oil and gas industry: Design, application and challenges</title><secondary-title>Applied Energy</secondary-title></titles><periodical><full-title>Applied Energy</full-title></periodical><pages>287-310</pages><volume>191</volume><dates><year>2017</year></dates><isbn>0306-2619</isbn><urls></urls></record></Cite></EndNote>28, even from none conventional resources ADDIN EN.CITE <EndNote><Cite><Author>Ogolo</Author><Year>2012</Year><RecNum>92</RecNum><DisplayText>15</DisplayText><record><rec-number>92</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525934204″>92</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Ogolo, NA</author><author>Olafuyi, OA</author><author>Onyekonwu, MO</author></authors></contributors><titles><title>Enhanced oil recovery using nanoparticles</title><secondary-title>SPE Saudi Arabia section technical symposium and exhibition</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613992300</isbn><urls></urls></record></Cite></EndNote>15.

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ADDIN EN.CITE.DATA 31-33. Based on their adsorption capability, nanoparticles also can extensively be used in overcoming production problems such as inhibiting asphaltene deposition and the subsequent formation damage ADDIN EN.CITE <EndNote><Cite><Author>Negin</Author><Year>2016</Year><RecNum>198</RecNum><DisplayText>34</DisplayText><record><rec-number>198</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>198</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Negin, Chegenizadeh</author><author>Ali, Saeedi</author><author>Xie, Quan</author></authors></contributors><titles><title>Application of nanotechnology for enhancing oil recovery–A review</title><secondary-title>Petroleum</secondary-title></titles><periodical><full-title>Petroleum</full-title></periodical><pages>324-333</pages><volume>2</volume><number>4</number><dates><year>2016</year></dates><isbn>2405-6561</isbn><urls></urls></record></Cite></EndNote>34. Some studies on the application of nanoparticles in EOR have concluded that nanoparticles, in terms of their size, can penetrate into the pore space where the conventional recovery techniques cannot reach, representing an advantage as they can change both the reservoir fluid properties and improve oil recovery ADDIN EN.CITE <EndNote><Cite><Author>Negin</Author><Year>2016</Year><RecNum>198</RecNum><DisplayText>34</DisplayText><record><rec-number>198</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>198</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Negin, Chegenizadeh</author><author>Ali, Saeedi</author><author>Xie, Quan</author></authors></contributors><titles><title>Application of nanotechnology for enhancing oil recovery–A review</title><secondary-title>Petroleum</secondary-title></titles><periodical><full-title>Petroleum</full-title></periodical><pages>324-333</pages><volume>2</volume><number>4</number><dates><year>2016</year></dates><isbn>2405-6561</isbn><urls></urls></record></Cite></EndNote>34. Several applications of nanoparticles in EOR have been extensively conducted mostly in laboratories to understand the phenomena under which nanoparticles enhance oil recovery, focusing on mechanisms such as interfacial tension reduction ADDIN EN.CITE <EndNote><Cite><Author>Hendraningrat</Author><Year>2013</Year><RecNum>176</RecNum><DisplayText>35</DisplayText><record><rec-number>176</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>176</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Hendraningrat, Luky</author><author>Li, Shidong</author><author>Torsater, Ole</author></authors></contributors><titles><title>Effect of some parameters influencing enhanced oil recovery process using silica nanoparticles: An experimental investigation</title><secondary-title>SPE Reservoir Characterization and Simulation Conference and Exhibition</secondary-title></titles><dates><year>2013</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613992688</isbn><urls></urls></record></Cite></EndNote>35, wettability alteration ADDIN EN.CITE <EndNote><Cite><Author>Giraldo</Author><Year>2013</Year><RecNum>87</RecNum><DisplayText>17</DisplayText><record><rec-number>87</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>87</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Giraldo, Juliana</author><author>Benjumea, Pedro</author><author>Lopera, Sergio</author><author>Corte?s, Farid B</author><author>Ruiz, Marco A</author></authors></contributors><titles><title>Wettability alteration of sandstone cores by alumina-based nanofluids</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3659-3665</pages><volume>27</volume><number>7</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>17, oil viscosity reduction ADDIN EN.CITE <EndNote><Cite><Author>Ehtesabi</Author><Year>2013</Year><RecNum>108</RecNum><DisplayText>36</DisplayText><record><rec-number>108</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>108</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Ehtesabi, Hamide</author><author>Ahadian, M Mahdi</author><author>Taghikhani, Vahid</author><author>Ghazanfari, M Hossein</author></authors></contributors><titles><title>Enhanced heavy oil recovery in sandstone cores using TiO2 nanofluids</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>423-430</pages><volume>28</volume><number>1</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>36, structural disjoining pressure ADDIN EN.CITE <EndNote><Cite><Author>Wasan</Author><Year>2011</Year><RecNum>59</RecNum><DisplayText>37</DisplayText><record><rec-number>59</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>59</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wasan, Darsh</author><author>Nikolov, Alex</author><author>Kondiparty, Kirti</author></authors></contributors><titles><title>The wetting and spreading of nanofluids on solids: Role of the structural disjoining pressure</title><secondary-title>Current Opinion in Colloid &amp; Interface Science</secondary-title></titles><periodical><full-title>Current Opinion in Colloid &amp; Interface Science</full-title></periodical><pages>344-349</pages><volume>16</volume><number>4</number><dates><year>2011</year></dates><isbn>1359-0294</isbn><urls></urls></record></Cite></EndNote>37, and how these mechanisms vary with different types, size and concentration of nanoparticles. Luky et al ADDIN EN.CITE <EndNote><Cite><Author>Hendraningrat</Author><Year>2012</Year><RecNum>132</RecNum><DisplayText>38</DisplayText><record><rec-number>132</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>132</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Hendraningrat, Luky</author><author>Shidong, Li</author></authors></contributors><titles><title>A glass micromodel experimental study of hydrophilic nanoparticles retention for EOR project</title><secondary-title>SPE Russian Oil and Gas Exploration and Production Technical Conference and Exhibition</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613992149</isbn><urls></urls></record></Cite></EndNote>38, conducted a study to investigate the impact of nanofluids injection on interfacial tension reduction, permeability impairment, nanoparticle retention and how these parameters contribute to oil recovery. They carried out their study in a glass micromodel and the microscopic visualization showed that nanoparticles are adsorbed at the glass surface due to the pressure log jamming that was observed during fluid injection; subsequently, the nanoparticle entrapment resulted into wettability alteration and at same time permeability impairment was noticed. The authors reported that nanoparticle size, type, and concentration are among the key parameters that effect nano-enhanced oil recovery (NANO-EOR). They concluded that increasing nanoparticle concentration can drastically reduce the IFT but also may result in a reduction of absolute permeability. Ali et al ADDIN EN.CITE <EndNote><Cite><Author>Esfandyari Bayat</Author><Year>2014</Year><RecNum>62</RecNum><DisplayText>39</DisplayText><record><rec-number>62</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>62</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Esfandyari Bayat, Ali</author><author>Junin, Radzuan</author><author>Samsuri, Ariffin</author><author>Piroozian, Ali</author><author>Hokmabadi, Mehrdad</author></authors></contributors><titles><title>Impact of Metal Oxide Nanoparticles on Enhanced Oil Recovery from Limestone Media at Several Temperatures</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>6255-6266</pages><volume>28</volume><number>10</number><dates><year>2014</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef5013616</electronic-resource-num></record></Cite></EndNote>39, investigated the impact of aluminium oxide (Al2O3), titanium dioxide (TiO2) and silica dioxide (SiO2) nanoparticles on enhanced oil recovery for a limestone media at several temperatures. At first, they carried out a transport study and found out that Al2O3 nanoparticles had the lowest adsorption rate of 8.2%, followed by TiO2 with 27.8% and finally the SiO2 with the highest adsorption rate of 43.4%. They also noticed that all these three nanoparticles could potentially change the wettability of the core from intermediate to strong water wet and reduce the capillary forces. Moreover, a considerable viscosity reduction in the presence of Al2O3 and TiO2 nanoparticles at 50 oC and 60 oC was noticed. Different researchers ADDIN EN.CITE <EndNote><Cite><Author>Ogolo</Author><Year>2012</Year><RecNum>92</RecNum><DisplayText>15, 40</DisplayText><record><rec-number>92</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525934204″>92</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Ogolo, NA</author><author>Olafuyi, OA</author><author>Onyekonwu, MO</author></authors></contributors><titles><title>Enhanced oil recovery using nanoparticles</title><secondary-title>SPE Saudi Arabia section technical symposium and exhibition</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613992300</isbn><urls></urls></record></Cite><Cite><Author>Hashemi</Author><Year>2014</Year><RecNum>93</RecNum><record><rec-number>93</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525934498″>93</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hashemi, Rohallah</author><author>Nassar, Nashaat N</author><author>Almao, Pedro Pereira</author></authors></contributors><titles><title>Nanoparticle technology for heavy oil in-situ upgrading and recovery enhancement: Opportunities and challenges</title><secondary-title>Applied Energy</secondary-title></titles><periodical><full-title>Applied Energy</full-title></periodical><pages>374-387</pages><volume>133</volume><dates><year>2014</year></dates><isbn>0306-2619</isbn><urls></urls></record></Cite></EndNote>15, 40 have used different nanomaterials for enhanced oil recovery featuring different mechanisms. The massive multiplicity of the nanomaterials (Figure 1) arising from their wide biochemical nature, sizes, morphologies and shapes, the dispersant in which the particles are present, the state of medium of the particles and most significantly, the numerous probable surface adjustments the nanoparticles can be exposed to make this an imperative active field of science. However, there are not so many available studies addressing the combination of the commonly used nanoparticles and the optimization of the oil recovery parameters. Therefore, this review presents the opportunities and major critique of the recently tested nanoparticles in EOR, focus on the underlying mechanisms of nanoparticles in EOR, recovery parameters involved during the enhancement processes, nanofluid stabilization techniques applicable to EOR have also been reviewed, environmental and health concerns raised due to nanomaterials exposure. Lastly, the challenges and opportunities of using nanomaterials in EOR have also been discussed in this review. At the end of this review, readers will be able to understand how to enhance oil recovery using nanofluids and how to reduce the risks associated with nanofluid floodings.

27749541910Engineered Nanoparticles
Shape
Spheres, Cubes, Cylinder, Hollow tubes, Hollow spheres, Core/shell structures
Dispersion State
Individually dispersed
Aggregated reversibly
Aggregated irreversibly
Ordered structure
Dispersion Medium
(Gels, Liquids Solid matrix, Gases
Surface Modification
Unmodified (as produced)
Surface treatment with silanes
Grafting polymers
Surface coating
Grafting charged ligand
Adsorbed surfactants/polymers
Chemical Nature
Metals, Metal oxides, Semiconductors, Polymers
Carbon
Biomolecules
Engineered Nanoparticles
Shape
Spheres, Cubes, Cylinder, Hollow tubes, Hollow spheres, Core/shell structures
Dispersion State
Individually dispersed
Aggregated reversibly
Aggregated irreversibly
Ordered structure
Dispersion Medium
(Gels, Liquids Solid matrix, Gases
Surface Modification
Unmodified (as produced)
Surface treatment with silanes
Grafting polymers
Surface coating
Grafting charged ligand
Adsorbed surfactants/polymers
Chemical Nature
Metals, Metal oxides, Semiconductors, Polymers
Carbon
Biomolecules

Figure 1. Various features contributing to the diversity of engineered nanoparticles.

2. Types of nanoparticles commonly used in enhancing oil recoveryThe chemical composition of crude oil such as viscosity and density change depending on source and location ADDIN EN.CITE <EndNote><Cite><Author>Speight</Author><Year>2014</Year><RecNum>94</RecNum><DisplayText>41, 42</DisplayText><record><rec-number>94</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525934734″>94</key></foreign-keys><ref-type name=”Book”>6</ref-type><contributors><authors><author>Speight, James G</author></authors></contributors><titles><title>The chemistry and technology of petroleum</title></titles><dates><year>2014</year></dates><publisher>CRC press</publisher><isbn>1439873895</isbn><urls></urls></record></Cite><Cite><Author>Mullins</Author><Year>2011</Year><RecNum>20</RecNum><record><rec-number>20</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1523396670″>20</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Mullins, Oliver C</author></authors></contributors><titles><title>The asphaltenes</title><secondary-title>Annual Review of Analytical Chemistry</secondary-title></titles><periodical><full-title>Annual Review of Analytical Chemistry</full-title></periodical><pages>393-418</pages><volume>4</volume><dates><year>2011</year></dates><isbn>1936-1327</isbn><urls></urls></record></Cite></EndNote>41, 42. Therefore, it is necessary to study the effect of various types of nanoparticles on a given type of oil. In this section, a detailed description of the most common nanoparticles that have been used and recommended for various reservoir formation in EOR processes are discussed.
2.1. Silica (SiO2) nanoparticles
In different parts of the world, silica or silicon dioxide is the major constituent of sand ADDIN EN.CITE <EndNote><Cite><Author>Pettijohn</Author><Year>2012</Year><RecNum>95</RecNum><DisplayText>43</DisplayText><record><rec-number>95</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525935223″>95</key></foreign-keys><ref-type name=”Book”>6</ref-type><contributors><authors><author>Pettijohn, Francis John</author><author>Potter, Paul E</author><author>Siever, Raymond</author></authors></contributors><titles><title>Sand and sandstone</title></titles><dates><year>2012</year></dates><publisher>Springer Science &amp; Business Media</publisher><isbn>1461210666</isbn><urls></urls></record></Cite></EndNote>43. It is an oxide of silicon with the chemical formula SiO2, most commonly found in nature as quartz and in various living organisms. These nanomaterials are environmentally friendly due to their vast existence in nature ADDIN EN.CITE <EndNote><Cite><Author>Darling</Author><Year>2011</Year><RecNum>206</RecNum><DisplayText>44</DisplayText><record><rec-number>206</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>206</key></foreign-keys><ref-type name=”Book”>6</ref-type><contributors><authors><author>Darling, Peter</author></authors></contributors><titles><title>SME mining engineering handbook</title></titles><volume>1</volume><dates><year>2011</year></dates><publisher>SME</publisher><isbn>0873352645</isbn><urls></urls></record></Cite></EndNote>44. Besides, the surface area of SiO2 barely changes even when heated at elevated temperatures (650 oC) making them thermally stable ADDIN EN.CITE <EndNote><Cite><Author>Wang</Author><Year>1999</Year><RecNum>207</RecNum><DisplayText>45</DisplayText><record><rec-number>207</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>207</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wang, Liwei</author><author>Wang, Zichen</author><author>Yang, Hua</author><author>Yang, Guangli</author></authors></contributors><titles><title>The study of thermal stability of the SiO2 powders with high specific surface area</title><secondary-title>Materials chemistry and physics</secondary-title></titles><periodical><full-title>Materials chemistry and physics</full-title></periodical><pages>260-263</pages><volume>57</volume><number>3</number><dates><year>1999</year></dates><isbn>0254-0584</isbn><urls></urls></record></Cite></EndNote>45, and appropriate for EOR applications especially in harsh reservoir conditions ADDIN EN.CITE <EndNote><Cite><Author>Wang</Author><Year>1999</Year><RecNum>211</RecNum><DisplayText>46</DisplayText><record><rec-number>211</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>211</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wang, Liwei</author><author>Wang, Zichen</author><author>Yang, Hua</author><author>Yang, Guangli</author></authors></contributors><titles><title>The study of thermal stability of the SiO 2 powders with high specific surface area</title><secondary-title>Materials chemistry and physics</secondary-title></titles><periodical><full-title>Materials chemistry and physics</full-title></periodical><pages>260-263</pages><volume>57</volume><number>3</number><dates><year>1999</year></dates><isbn>0254-0584</isbn><urls></urls></record></Cite></EndNote>46. Current studies have embarked on the application of these types of nanoparticles for oil enhancement either alone or synergised with various conventional EOR methodsPEVuZE5vdGU+PENpdGU+PEF1dGhvcj5NaXJhbmRhPC9BdXRob3I+PFllYXI+MjAxMjwvWWVhcj48
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ADDIN EN.CITE.DATA 13, 47-49. Foresentence, Zargartalebi et al. ADDIN EN.CITE <EndNote><Cite><Author>Zargartalebi</Author><Year>2015</Year><RecNum>55</RecNum><DisplayText>50</DisplayText><record><rec-number>55</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>55</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Zargartalebi, Mohammad</author><author>Kharrat, Riyaz</author><author>Barati, Nasim</author></authors></contributors><titles><title>Enhancement of surfactant flooding performance by the use of silica nanoparticles</title><secondary-title>Fuel</secondary-title></titles><periodical><full-title>Fuel</full-title></periodical><pages>21-27</pages><volume>143</volume><dates><year>2015</year></dates><isbn>00162361</isbn><urls></urls><electronic-resource-num>10.1016/j.fuel.2014.11.040</electronic-resource-num></record></Cite></EndNote>50 improved surfactant oil enhancement using SiO2 by using modified silica, the hydrophilic and hydrophobic type, together with an anionic surfactant. They performed an extensive series of measurements for interfacial tension and adsorption and observed a reduction in surfactant adsorption and interfacial tension in the presence of these nanoparticles. They concluded that the performance of surfactant flooding can be significantly improved by the addition of an optimized concentration of SiO2 nanoparticles. Luky et al. ADDIN EN.CITE <EndNote><Cite><Author>Jain</Author><Year>2009</Year><RecNum>171</RecNum><DisplayText>51</DisplayText><record><rec-number>171</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>171</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Jain, Nirmesh</author><author>Wang, Yanjun</author><author>Jones, Stephen K</author><author>Hawkett, Brian S</author><author>Warr, Gregory G</author></authors></contributors><titles><title>Optimized steric stabilization of aqueous ferrofluids and magnetic nanoparticles</title><secondary-title>Langmuir</secondary-title></titles><periodical><full-title>Langmuir</full-title></periodical><pages>4465-4472</pages><volume>26</volume><number>6</number><dates><year>2009</year></dates><isbn>0743-7463</isbn><urls></urls></record></Cite></EndNote>51, conducted a conclusive study, on the effect of particle size, permeability, initial rock wettability, injection rate, and temperature using silica nanoparticles, and concluded that small particle size increases oil recovery and displacement efficiency due to the reduction of the contact angle as the size decreases. The author also reported that highest recoveries were obtained from the intermediate wet system, increasing the injection rate reduced the oil recovery while increasing the temperature resulted into incremental oil recovery. The main recovery mechanism of SiO2 has been reported to be mainly wettability alteration due to adsorption on the rock surface and, generally, it is the most widely and recommended EOR nano-type agent for all wettability conditions but performs best in mainly sandstone reservoirs. Moreover, compared to other nanoparticle types with the same concentration, the adsorption behaviour of silica nanoparticles has been reported not to result in significant porosity and permeability impairment especially in sandstone formations ADDIN EN.CITE <EndNote><Cite><Author>Yu</Author><Year>2012</Year><RecNum>187</RecNum><DisplayText>52</DisplayText><record><rec-number>187</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>187</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Yu, Jianjia</author><author>An, Cheng</author><author>Mo, Di</author><author>Liu, Ning</author><author>Lee, Robert L</author></authors></contributors><titles><title>Study of adsorption and transportation behavior of nanoparticles in three different porous media</title><secondary-title>SPE improved oil recovery symposium</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613991975</isbn><urls></urls></record></Cite></EndNote>52. Notwithstanding their great recovery potential and ability to enhance oil recovery, silica nanoparticles still suffer difficulty of reducing the interfacial tension to very ultra-low values compared to conventional surfactants. Although Roustaei et al. ADDIN EN.CITE <EndNote><Cite><Author>Roustaei</Author><Year>2012</Year><RecNum>223</RecNum><DisplayText>53</DisplayText><record><rec-number>223</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>223</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Roustaei, Abbas</author><author>Moghadasi, Jamshid</author><author>Bagherzadeh, Hadi</author><author>Shahrabadi, Abbas</author></authors></contributors><titles><title>An experimental investigation of polysilicon nanoparticles&apos; recovery efficiencies through changes in interfacial tension and wettability alteration</title><secondary-title>SPE international oilfield nanotechnology conference and exhibition</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613992068</isbn><urls></urls></record></Cite></EndNote>53, reported a drastic decrease in oil-water IFT, from 26.3mN/m to 1.75 mN/m using lipophilic polysilicon this is considered premature since a different trend was reported by Onyekonwu et al ADDIN EN.CITE <EndNote><Cite><Author>Onyekonwu</Author><Year>2010</Year><RecNum>224</RecNum><DisplayText>54</DisplayText><record><rec-number>224</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>224</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Onyekonwu, Mike O</author><author>Ogolo, Naomi A</author></authors></contributors><titles><title>Investigating the use of nanoparticles in enhancing oil recovery</title><secondary-title>Nigeria Annual international conference and exhibition</secondary-title></titles><dates><year>2010</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1555633013</isbn><urls></urls></record></Cite></EndNote>54, for the same polysilicon nanoparticles. Moreover, in both studies ethanol was used as a dispersing phase for the polysilicon and IFT reduction might have been caused by the presence of ethanol but not the polysilicon nanoparticles alone, hence more research is still needed. Also, most studies are focusing on using commercial silica which has limited its applicability in industrial, pilot, and field testing. Therefore, synthesis pathways that are not only environmentally friendly but also cost-effective are still needed that can offer options for scalability for pilot and field testing applications. However, from the aforementioned analysis, it is obvious to anticipate that the use of silica nanoparticles in EOR offers many advantages compared to other nanoparticles especially in sandstone reservoirs, owing to their physical structure and affinity. Although, most of the reported works on this matter are still experimental studies conducted on a bench scale level and no real process or field application has been reported. Hence, to have a clear understanding on the role of silica nanoparticles in EOR, more laboratory investigations at reservoir conditions and pilot scale testing are needed and are of paramount importance to have a clear understanding of their ability to be accepted in the oil and gas industry. The highlights of some of the studies that have been performed using silica NPs to enhance oil recovery can be found in Table 1 attached.

2.2. Aluminium oxide (Al2O3) nanoparticles
Al2O3 is a white powder composed of nanoparticles of alpha-phase aluminium oxide, the naturally-occurring form of aluminium oxide or corundum. Al2O3 nanopowder Particles typically range from 40-10um nm, depending on, purity standards, modifications, and application. Because of its wide availability, several researchers have used it for enhancing oil recoveryPEVuZE5vdGU+PENpdGU+PEF1dGhvcj5PZ29sbzwvQXV0aG9yPjxZZWFyPjIwMTI8L1llYXI+PFJl
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ADDIN EN.CITE.DATA 15, 39, 55 etc. The main mechanism deduced for improving oil recovery using this type of nanomaterial has been mainly a viscosity reduction ADDIN EN.CITE <EndNote><Cite><Author>Esfandyari Bayat</Author><Year>2014</Year><RecNum>62</RecNum><DisplayText>39, 56</DisplayText><record><rec-number>62</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>62</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Esfandyari Bayat, Ali</author><author>Junin, Radzuan</author><author>Samsuri, Ariffin</author><author>Piroozian, Ali</author><author>Hokmabadi, Mehrdad</author></authors></contributors><titles><title>Impact of Metal Oxide Nanoparticles on Enhanced Oil Recovery from Limestone Media at Several Temperatures</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>6255-6266</pages><volume>28</volume><number>10</number><dates><year>2014</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef5013616</electronic-resource-num></record></Cite><Cite><Author>Zaid</Author><Year>2014</Year><RecNum>208</RecNum><record><rec-number>208</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>208</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Zaid, Hasnah Mohd</author><author>Latiff, Ahmad</author><author>Rasyada, Noor</author><author>Yahya, Noorhana</author></authors></contributors><titles><title>The Effect of Zinc Oxide and Aluminum Oxide Nanoparticles on Interfacial Tension and Viscosity of Nanofluids for Enhanced Oil Recovery</title><secondary-title>Advanced Materials Research</secondary-title></titles><pages>56-59</pages><volume>1024</volume><dates><year>2014</year></dates><publisher>Trans Tech Publ</publisher><isbn>3038352136</isbn><urls></urls></record></Cite></EndNote>39, 56. Studies have been conducted either using it alone or synergising it with other EOR conventional methods. Zaid et al ADDIN EN.CITE <EndNote><Cite><Author>Zaid</Author><Year>2014</Year><RecNum>213</RecNum><DisplayText>56</DisplayText><record><rec-number>213</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>213</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Zaid, Hasnah Mohd</author><author>Latiff, Ahmad</author><author>Rasyada, Noor</author><author>Yahya, Noorhana</author></authors></contributors><titles><title>The Effect of Zinc Oxide and Aluminum Oxide Nanoparticles on Interfacial Tension and Viscosity of Nanofluids for Enhanced Oil Recovery</title><secondary-title>Advanced Materials Research</secondary-title></titles><pages>56-59</pages><volume>1024</volume><dates><year>2014</year></dates><publisher>Trans Tech Publ</publisher><isbn>3038352136</isbn><urls></urls></record></Cite></EndNote>56, compared the effectiveness of Al2O3 and zinc oxide (ZnO) on EOR. In their study, they measured interfacial tension in the presence of nanofluids and the change in oil viscosity for various nanofluids concentrations. Core flooding experiments were conducted and the oil recovery efficiency when nanofluids were injected was compared to that of the commercial surfactant, 0.3 wt% sodium dodecyl sulfate (SDS) alone. 11.7 % increase in the recovery was obtained after injection of Al2O3 nanofluids, compared to 0.3wt% SDS. Again, based on the nano-type, 5.12% more oil was recovered by Al2O3 compared to ZnO-based nanofluids. The performance of anionic surfactant as wettability modifiers in sandstone cores can be improved by dispersing 100 ppm of alumina nanoparticles in the surfactant ADDIN EN.CITE <EndNote><Cite><Author>Giraldo</Author><Year>2013</Year><RecNum>214</RecNum><DisplayText>17</DisplayText><record><rec-number>214</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>214</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Giraldo, Juliana</author><author>Benjumea, Pedro</author><author>Lopera, Sergio</author><author>Corte?s, Farid B</author><author>Ruiz, Marco A</author></authors></contributors><titles><title>Wettability alteration of sandstone cores by alumina-based nanofluids</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3659-3665</pages><volume>27</volume><number>7</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>17. The author concluded that alumina-based nanofluids can improve the water flooding oil recovery efficiency in sandstone cores by altering the wettability of the cores from strongly oil wet to strong water wet. Notwithstanding their potential to improve oil recovery, in comparison to SiO2 and TiO2, Al2O3 nanoparticles have been reported to be unstable especially in a brine of higher ionic strength ADDIN EN.CITE <EndNote><Cite><Author>Hendraningrat</Author><Year>2015</Year><RecNum>216</RecNum><DisplayText>57</DisplayText><record><rec-number>216</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>216</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hendraningrat, Luky</author><author>Torsæter, Ole</author></authors></contributors><titles><title>Metal oxide-based nanoparticles: revealing their potential to enhance oil recovery in different wettability systems</title><secondary-title>Applied Nanoscience</secondary-title></titles><periodical><full-title>Applied Nanoscience</full-title></periodical><pages>181-199</pages><volume>5</volume><number>2</number><dates><year>2015</year></dates><isbn>2190-5509</isbn><urls></urls></record></Cite></EndNote>57. They tend to aggregate and form clusters that may impair the permeability during the flooding process especially in sandstone formations ADDIN EN.CITE <EndNote><Cite><Author>Bayat</Author><Year>2015</Year><RecNum>222</RecNum><DisplayText>58</DisplayText><record><rec-number>222</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>222</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Bayat, Ali Esfandyari</author><author>Junin, Radzuan</author></authors></contributors><titles><title>Transportation of metal oxide nanoparticles through various porous media for enhanced oil recovery</title><secondary-title>SPE/IATMI Asia Pacific Oil &amp; Gas Conference and Exhibition</secondary-title></titles><dates><year>2015</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613993900</isbn><urls></urls></record></Cite></EndNote>58. Similar to SiO2, Al2O3 also do not reduce the interfacial tension to very low ultra values compared. Also, economical synthesis pathways that are not only environmentally friendly but also cost-effective are still needed that can offer options for scalability to pilot and field testing applications. Likely, from the above-mentioned analysis it is clear that the application of alumina-based nanoparticles in EOR offers many merits, due to their physical structure and surface morphologies although still, most of the reported work on the application of Al2O3 in EOR is at lab scale and at ambient conditions. Although alumina nanoparticles were successfully tested for field applications and gave promising results ADDIN EN.CITE <EndNote><Cite><Author>Zabala</Author><Year>2014</Year><RecNum>262</RecNum><DisplayText>59</DisplayText><record><rec-number>262</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>262</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Zabala, R</author><author>Mora, E</author><author>Botero, OF</author><author>Cespedes, C</author><author>Guarin, L</author><author>Franco, CA</author><author>Cortes, FB</author><author>Patino, JE</author><author>Ospina, N</author></authors></contributors><titles><title>Nano-technology for asphaltenes inhibition in Cupiagua South Wells</title><secondary-title>IPTC 2014: International Petroleum Technology Conference</secondary-title></titles><dates><year>2014</year></dates><isbn>2214-4609</isbn><urls></urls></record></Cite></EndNote>59, to have a clear understanding on their performance, more laboratory investigations, pilot scale and field testing are still required to have a clear understanding of their ability to be adopted in the oil and gas industry. The highlights of some of the studies that have been performed using Al2O3 NPs to enhance oil recovery can be found in Table 1 attached.

2.3. Nickel oxide (NiO) nanoparticles
Nickel (II) oxide (NiO) is notably a well-characterized oxide of nickel. It is classified as a basic metal oxide. NiO is an important transition metal oxide with cubic lattice structure and has attracted increasing attention owing to its potential use in various applications. It is widely used as a catalyst during aquathermolysis processes for heavy oil upgrading ADDIN EN.CITE <EndNote><Cite><Author>Mukherjee</Author><Year>2001</Year><RecNum>175</RecNum><DisplayText>60, 61</DisplayText><record><rec-number>175</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>175</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Mukherjee, Priyabrata</author><author>Ahmad, Absar</author><author>Mandal, Deendayal</author><author>Senapati, Satyajyoti</author><author>Sainkar, Sudhakar R</author><author>Khan, Mohammad I</author><author>Parishcha, Renu</author><author>Ajaykumar, PV</author><author>Alam, Mansoor</author><author>Kumar, Rajiv</author></authors></contributors><titles><title>Fungus-mediated synthesis of silver nanoparticles and their immobilization in the mycelial matrix: a novel biological approach to nanoparticle synthesis</title><secondary-title>Nano Letters</secondary-title></titles><periodical><full-title>Nano Letters</full-title></periodical><pages>515-519</pages><volume>1</volume><number>10</number><dates><year>2001</year></dates><isbn>1530-6984</isbn><urls></urls></record></Cite><Cite><Author>Meyers</Author><Year>2006</Year><RecNum>176</RecNum><record><rec-number>176</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>176</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Meyers, Marc A</author><author>Mishra, A</author><author>Benson, David J</author></authors></contributors><titles><title>Mechanical properties of nanocrystalline materials</title><secondary-title>Progress in materials science</secondary-title></titles><periodical><full-title>Progress in materials science</full-title></periodical><pages>427-556</pages><volume>51</volume><number>4</number><dates><year>2006</year></dates><isbn>0079-6425</isbn><urls></urls></record></Cite></EndNote>60, 61. Sayed et al. ADDIN EN.CITE <EndNote><Cite><Author>Hashemi</Author><Year>2016</Year><RecNum>207</RecNum><DisplayText>62</DisplayText><record><rec-number>207</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>207</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hashemi, Seyed Iman</author><author>Fazelabdolabadi, Babak</author><author>Moradi, Siyamak</author><author>Rashidi, Ali Morad</author><author>Shahrabadi, Abbas</author><author>Bagherzadeh, Hadi</author></authors></contributors><titles><title>On the application of NiO nanoparticles to mitigate in situ asphaltene deposition in carbonate porous matrix</title><secondary-title>Applied Nanoscience</secondary-title></titles><periodical><full-title>Applied Nanoscience</full-title></periodical><pages>71-81</pages><volume>6</volume><number>1</number><dates><year>2016</year></dates><isbn>2190-5509</isbn><urls></urls></record></Cite></EndNote>62, explored the effect of NiO nanoparticles for asphaltene disaggregation in porous media. In the presence of carbon dioxide, the NiO nanoparticles were injected in the porous medium via gas steam injection, in which they were uniformly dispersed using polydimethylsiloxane (PDMS). The results showed that under miscible CO2 state, there was a considerable improvement in permeability and porosity reduction of the core, as well as less asphaltene deposition in porous media, which increased the oil recovery factor after NiO nanoparticles had been applied. The dominant mechanism for NiO types of nanomaterials has been reported to be mainly viscosity reduction due to asphaltene disaggregation especially in heavy oil ADDIN EN.CITE <EndNote><Cite><Author>Negin</Author><Year>2016</Year><RecNum>198</RecNum><DisplayText>34</DisplayText><record><rec-number>198</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>198</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Negin, Chegenizadeh</author><author>Ali, Saeedi</author><author>Xie, Quan</author></authors></contributors><titles><title>Application of nanotechnology for enhancing oil recovery–A review</title><secondary-title>Petroleum</secondary-title></titles><periodical><full-title>Petroleum</full-title></periodical><pages>324-333</pages><volume>2</volume><number>4</number><dates><year>2016</year></dates><isbn>2405-6561</isbn><urls></urls></record></Cite></EndNote>34. Ogolo et al. ADDIN EN.CITE <EndNote><Cite><Author>Ogolo</Author><Year>2012</Year><RecNum>92</RecNum><DisplayText>15</DisplayText><record><rec-number>92</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525934204″>92</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Ogolo, NA</author><author>Olafuyi, OA</author><author>Onyekonwu, MO</author></authors></contributors><titles><title>Enhanced oil recovery using nanoparticles</title><secondary-title>SPE Saudi Arabia section technical symposium and exhibition</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613992300</isbn><urls></urls></record></Cite></EndNote>15, conducted a study on different types of nanoparticles which included NiO, the results indicated that NiO nanoparticles are good EOR agents, however, the authors found that more recovery can be enhanced using ethanol as the dispersing agent other than brine. Reduction of oil viscosity still was reported as the main mechanism for oil recovery increment. The highlights of some of the studies that have been performed using NiO NPs to enhance oil recovery can be found in Table 1 attached.

2.4. Zinc oxide (ZnO) nanoparticles
Using ZnO in enhancing oil recovery is still limited as several researchers reported its negative impact on the reservoir permeability ADDIN EN.CITE <EndNote><Cite><Author>Ogolo</Author><Year>2012</Year><RecNum>92</RecNum><DisplayText>15</DisplayText><record><rec-number>92</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525934204″>92</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Ogolo, NA</author><author>Olafuyi, OA</author><author>Onyekonwu, MO</author></authors></contributors><titles><title>Enhanced oil recovery using nanoparticles</title><secondary-title>SPE Saudi Arabia section technical symposium and exhibition</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613992300</isbn><urls></urls></record></Cite></EndNote>15. However, these nanoparticles exhibit antibacterial, anti-corrosive, antifungal and UV filtering properties. Because of its higher density (5600 kg/m3), ZnO has found many applications in rubber making ADDIN EN.CITE <EndNote><Cite><Author>Gardiner</Author><Year>1970</Year><RecNum>234</RecNum><DisplayText>63, 64</DisplayText><record><rec-number>234</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>234</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Gardiner, J Brooke</author></authors></contributors><titles><title>Studies in the Morphology and vulcanization of gum rubber blends</title><secondary-title>Rubber Chemistry and Technology</secondary-title></titles><periodical><full-title>Rubber Chemistry and Technology</full-title></periodical><pages>370-399</pages><volume>43</volume><number>2</number><dates><year>1970</year></dates><isbn>0035-9475</isbn><urls></urls></record></Cite><Cite><Author>Lin</Author><Year>2015</Year><RecNum>235</RecNum><record><rec-number>235</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>235</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Lin, Yong</author><author>Zeng, Zhikai</author><author>Zhu, Jiarong</author><author>Chen, Song</author><author>Yuan, Xue</author><author>Liu, Lan</author></authors></contributors><titles><title>Graphene nanosheets decorated with ZnO nanoparticles: facile synthesis and promising application for enhancing the mechanical and gas barrier properties of rubber nanocomposites</title><secondary-title>RSC Advances</secondary-title></titles><periodical><full-title>RSC Advances</full-title></periodical><pages>57771-57780</pages><volume>5</volume><number>71</number><dates><year>2015</year></dates><urls></urls></record></Cite></EndNote>63, 64, the ceramic industry ADDIN EN.CITE <EndNote><Cite><Author>Sousa</Author><Year>1999</Year><RecNum>236</RecNum><DisplayText>65</DisplayText><record><rec-number>236</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>236</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Sousa, VC</author><author>Segadaes, AM</author><author>Morelli, MR</author><author>Kiminami, RHGA</author></authors></contributors><titles><title>Combustion synthesized ZnO powders for varistor ceramics</title><secondary-title>International Journal of Inorganic Materials</secondary-title></titles><periodical><full-title>International Journal of Inorganic Materials</full-title></periodical><pages>235-241</pages><volume>1</volume><number>3-4</number><dates><year>1999</year></dates><isbn>1466-6049</isbn><urls></urls></record></Cite></EndNote>65, and as additives in cement and in various paints as a coating agent ADDIN EN.CITE <EndNote><Cite><Author>Oprea</Author><Year>2014</Year><RecNum>237</RecNum><DisplayText>66, 67</DisplayText><record><rec-number>237</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>237</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Oprea, Ovidiu</author><author>Andronescu, Ecaterina</author><author>Ficai, Denisa</author><author>Ficai, Anton</author><author>N Oktar, Faik</author><author>Yetmez, Mehmet</author></authors></contributors><titles><title>ZnO applications and challenges</title><secondary-title>Current Organic Chemistry</secondary-title></titles><periodical><full-title>Current Organic Chemistry</full-title></periodical><pages>192-203</pages><volume>18</volume><number>2</number><dates><year>2014</year></dates><isbn>1385-2728</isbn><urls></urls></record></Cite><Cite><Author>Moezzi</Author><Year>2012</Year><RecNum>238</RecNum><record><rec-number>238</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>238</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Moezzi, Amir</author><author>McDonagh, Andrew M</author><author>Cortie, Michael B</author></authors></contributors><titles><title>Zinc oxide particles: Synthesis, properties and applications</title><secondary-title>Chemical engineering journal</secondary-title></titles><periodical><full-title>Chemical Engineering Journal</full-title></periodical><pages>1-22</pages><volume>185</volume><dates><year>2012</year></dates><isbn>1385-8947</isbn><urls></urls></record></Cite></EndNote>66, 67. The highlights of some of the studies that have been performed using ZnO NPs to enhance oil recovery can be found in Table 1 attached.

2.5. Iron oxide nanoparticles
These types of nanomaterials mainly exist in two forms, magnetite (Fe3O4) and its oxidized form maghemite (?-Fe2O3). These nanoparticles are known for their superparamagnetic properties that lead to their potential applications in many electrical and magnetic fields, where they may be used as sensors and data storage ADDIN EN.CITE <EndNote><Cite><Author>Negin</Author><Year>2016</Year><RecNum>198</RecNum><DisplayText>34</DisplayText><record><rec-number>198</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>198</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Negin, Chegenizadeh</author><author>Ali, Saeedi</author><author>Xie, Quan</author></authors></contributors><titles><title>Application of nanotechnology for enhancing oil recovery–A review</title><secondary-title>Petroleum</secondary-title></titles><periodical><full-title>Petroleum</full-title></periodical><pages>324-333</pages><volume>2</volume><number>4</number><dates><year>2016</year></dates><isbn>2405-6561</isbn><urls></urls></record></Cite></EndNote>34. In oil enhancement, however, they are used as catalysts, especially for heavy oil upgrading. The main mechanism has been reported to be viscosity reduction due to asphaltene adsorption in heavy oil ADDIN EN.CITE <EndNote><Cite><Author>Taborda</Author><Year>2017</Year><RecNum>147</RecNum><DisplayText>68, 69</DisplayText><record><rec-number>147</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>147</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Taborda, Esteban A.</author><author>Franco, Camilo A.</author><author>Ruiz, Marco A.</author><author>Alvarado, Vladimir</author><author>Cortés, Farid B.</author></authors></contributors><titles><title>Experimental and Theoretical Study of Viscosity Reduction in Heavy Crude Oils by Addition of Nanoparticles</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1329-1338</pages><volume>31</volume><number>2</number><dates><year>2017</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/acs.energyfuels.6b02686</electronic-resource-num></record></Cite><Cite><Author>Kazemzadeh</Author><Year>2015</Year><RecNum>210</RecNum><record><rec-number>210</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>210</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Kazemzadeh, Yousef</author><author>Eshraghi, S Ehsan</author><author>Kazemi, Keyvan</author><author>Sourani, Saeed</author><author>Mehrabi, Mehran</author><author>Ahmadi, Yaser</author></authors></contributors><titles><title>Behavior of asphaltene adsorption onto the metal oxide nanoparticle surface and its effect on heavy oil recovery</title><secondary-title>Industrial &amp; Engineering Chemistry Research</secondary-title></titles><periodical><full-title>Industrial &amp; Engineering Chemistry Research</full-title></periodical><pages>233-239</pages><volume>54</volume><number>1</number><dates><year>2015</year></dates><isbn>0888-5885</isbn><urls></urls></record></Cite></EndNote>68, 69. Several studies have also reported promising results with the use of iron oxide in in-situ upgrading processes ADDIN EN.CITE <EndNote><Cite><Author>Hashemi</Author><Year>2013</Year><RecNum>212</RecNum><DisplayText>70, 71</DisplayText><record><rec-number>212</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>212</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hashemi, Rohallah</author><author>Nassar, Nashaat N</author><author>Pereira Almao, Pedro</author></authors></contributors><titles><title>Enhanced heavy oil recovery by in situ prepared ultradispersed multimetallic nanoparticles: A study of hot fluid flooding for Athabasca bitumen recovery</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2194-2201</pages><volume>27</volume><number>4</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite><Cite><Author>Nassar</Author><Year>2010</Year><RecNum>213</RecNum><record><rec-number>213</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>213</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nassar, Nashaat N</author><author>Husein, Maen M</author></authors></contributors><titles><title>Ultradispersed particles in heavy oil: Part I, preparation and stabilization of iron oxide/hydroxide</title><secondary-title>Fuel Processing Technology</secondary-title></titles><periodical><full-title>Fuel Processing Technology</full-title></periodical><pages>164-168</pages><volume>91</volume><number>2</number><dates><year>2010</year></dates><isbn>0378-3820</isbn><urls></urls></record></Cite></EndNote>70, 71. To the best of our findings, this nanoparticle type has been applied mainly in oil upgrading and viscosity reduction has been reported major underlying mechanism for oil recovery. The highlights of some of the studies that have been performed using Fe3O4 NPs to enhance oil recovery can be found in Table 1 attached.

2.6. Zirconium oxide (ZrO2) nanoparticles
This nanomaterial is in the form of a white powder composed of particles of zirconium oxide, also known as zirconia. It is used across a variety of fields for applications ranging from polishing semiconductors, ceramics, to producing artificial jewellery ADDIN EN.CITE <EndNote><Cite><Author>Nassar</Author><Year>2012</Year><RecNum>177</RecNum><DisplayText>72</DisplayText><record><rec-number>177</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>177</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nassar, Nashaat N</author></authors></contributors><titles><title>Iron oxide nanoadsorbents for removal of various pollutants from wastewater: an overview</title><secondary-title>Application of Adsorbents for Water Pollution Control</secondary-title></titles><periodical><full-title>Application of Adsorbents for Water Pollution Control</full-title></periodical><pages>81-118</pages><dates><year>2012</year></dates><urls></urls></record></Cite></EndNote>72. Zirconium is produced when ions in zirconia are replaced with yttrium, stabilizing the cubic phase of the material. This, in turn, makes it possible to produce sintered zirconium oxide products and allows the material to conduct certain ions. The use of these types of nanomaterials in the oil and gas industry is still novel, and few findings have been reported. ZrO2 nanoparticle efficiency at different nanoparticle concentrations (0-0.05 wt. %) was assessed through contact angle measurements. The results from the experimental findings showed that ZrO2 nanofluids have great potential in changing oil-wet limestone to the strongly water-wet condition. However, the best performance was observed at 0.05 wt% ZrO2 nanoparticle concentration which changed an originally strongly oil-wet (152°) calcite substrate towards a strongly water-wet (44°) state. The author concluded that ZrO2 is a good agent for enhanced oil recovery ADDIN EN.CITE <EndNote><Cite><Author>Nwidee</Author><Year>2016</Year><RecNum>214</RecNum><DisplayText>73</DisplayText><record><rec-number>214</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>214</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Nwidee, Lezorgia</author><author>Al-Anssari, Sarmad</author><author>Barifcani, Ahmed</author><author>Sarmadivaleh, Mohammad</author><author>Iglauer, Stefan</author></authors></contributors><titles><title>Nanofluids for enhanced oil recovery processes: wettability alteration using zirconium oxide</title><secondary-title>Offshore Technology Conference Asia</secondary-title></titles><dates><year>2016</year></dates><publisher>Offshore Technology Conference</publisher><isbn>1613993919</isbn><urls></urls></record></Cite></EndNote>73. Similar studies were conducted by Karim et al. ADDIN EN.CITE <EndNote><Cite><Author>Karimi</Author><Year>2012</Year><RecNum>141</RecNum><DisplayText>74</DisplayText><record><rec-number>141</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>141</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Karimi, Ali</author><author>Fakhroueian, Zahra</author><author>Bahramian, Alireza</author><author>Pour Khiabani, Nahid</author><author>Darabad, Jabar Babaee</author><author>Azin, Reza</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Wettability alteration in carbonates using zirconium oxide nanofluids: EOR implications</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1028-1036</pages><volume>26</volume><number>2</number><dates><year>2012</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>74, who used ZrO2 for wettability alteration together with a non-ionic surfactant for a carbonate rock. The authors reported that the nanomaterials used successfully altered the wettability from strongly oil-wet to strongly water-wet and that more oil could be recovered by spontaneous imbibition. However, the adsorption and growth of ZrO2 nanoparticles on the rock surface was a slow process that required at least two days. In recent studies, ZrO2 has been reported to displays superior thermal and chemical stability compared to alumina and silica nanoparticles ADDIN EN.CITE <EndNote><Cite><Author>Petit</Author><Year>2015</Year><RecNum>272</RecNum><DisplayText>75</DisplayText><record><rec-number>272</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>272</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Petit, Marc</author><author>Monot, Julien</author></authors></contributors><titles><title>Functionalization of Zirconium Oxide Surfaces</title><secondary-title>Chemistry of Organo-Hybrids: Synthesis and Characterization of Functional Nano-Objects</secondary-title></titles><periodical><full-title>Chemistry of Organo-Hybrids: Synthesis and Characterization of Functional Nano-Objects</full-title></periodical><pages>168-199</pages><dates><year>2015</year></dates><urls></urls></record></Cite></EndNote>75. Moreover, silica and ?-alumina nanoparticles were reported to exhibit limited chemical and physical stability compared with ZrO2 nanoparticle ADDIN EN.CITE <EndNote><Cite><Author>Gopalan</Author><Year>1995</Year><RecNum>273</RecNum><DisplayText>76</DisplayText><record><rec-number>273</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>273</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Gopalan, R</author><author>Chang, C-H</author><author>Lin, YS</author></authors></contributors><titles><title>Thermal stability improvement on pore and phase structure of sol-gel derived zirconia</title><secondary-title>Journal of materials science</secondary-title></titles><periodical><full-title>Journal of materials science</full-title></periodical><pages>3075-3081</pages><volume>30</volume><number>12</number><dates><year>1995</year></dates><isbn>0022-2461</isbn><urls></urls></record></Cite></EndNote>76. ZrO2 has a high catalytic effect and is reported to be the only metal oxide with four chemical properties on the surface: acidic/basic and reducing/oxidizing properties ADDIN EN.CITE <EndNote><Cite><Author>Tanabe</Author><Year>1985</Year><RecNum>271</RecNum><DisplayText>77</DisplayText><record><rec-number>271</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>271</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Tanabe, Kozo</author></authors></contributors><titles><title>Surface and catalytic properties of ZrO2</title><secondary-title>Materials chemistry and physics</secondary-title></titles><periodical><full-title>Materials chemistry and physics</full-title></periodical><pages>347-364</pages><volume>13</volume><number>3-4</number><dates><year>1985</year></dates><isbn>0254-0584</isbn><urls></urls></record></Cite></EndNote>77. From the aforementioned studies likely, it is clear that application of ZrO2 nanoparticles in EOR is mostly in carbonates formation and at lab scale. Therefore, to have a clear understanding on their performance in sandstone and at the reservoir, conditions more investigations are still needed in order to have a clear understanding of their underlying mechanism so that they can be adopted in the oil and gas industry. The highlights of some of the studies that have been performed using ZrO2 NPs to enhance oil recovery can be found in Table 1 attached.

2.7. Graphene oxide (GOs)
Graphene oxide is a compound of graphene, oxygen and hydrogen. It has many applications in various fields, especially in modern technology. Graphene oxide can be used in light emitting diodes (LEDs) and solar cell devices in electronics ADDIN EN.CITE <EndNote><Cite><Author>Wang</Author><Year>2008</Year><RecNum>228</RecNum><DisplayText>78, 79</DisplayText><record><rec-number>228</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>228</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wang, Xuan</author><author>Zhi, Linjie</author><author>Müllen, Klaus</author></authors></contributors><titles><title>Transparent, conductive graphene electrodes for dye-sensitized solar cells</title><secondary-title>Nano letters</secondary-title></titles><periodical><full-title>Nano letters</full-title></periodical><pages>323-327</pages><volume>8</volume><number>1</number><dates><year>2008</year></dates><isbn>1530-6984</isbn><urls></urls></record></Cite><Cite><Author>Jo</Author><Year>2012</Year><RecNum>233</RecNum><record><rec-number>233</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>233</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Jo, Gunho</author><author>Choe, Minhyeok</author><author>Lee, Sangchul</author><author>Park, Woojin</author><author>Kahng, Yung Ho</author><author>Lee, Takhee</author></authors></contributors><titles><title>The application of graphene as electrodes in electrical and optical devices</title><secondary-title>Nanotechnology</secondary-title></titles><periodical><full-title>Nanotechnology</full-title></periodical><pages>112001</pages><volume>23</volume><number>11</number><dates><year>2012</year></dates><isbn>0957-4484</isbn><urls></urls></record></Cite></EndNote>78, 79. Scientists are always looking for ways to increase the capacity and efficiency of energy storage, and advances in the processes to make graphene oxide have aided in this search. It is used as a material for energy storage in supercapacitorsPEVuZE5vdGU+PENpdGU+PEF1dGhvcj5TdG9sbGVyPC9BdXRob3I+PFllYXI+MjAwODwvWWVhcj48
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ADDIN EN.CITE.DATA 80-82. Its application in enhancing oil recovery has been recently reported. GOs was applied to improve the viscosity stability of diluted polymer/seawater solutions aged at reservoir conditions. In the presence of 300 ppm of GOs, the viscosity stability of 1700 ppm acrylamide-based polymer in a sea-water solution increased from 92 °C to 135 °C. ADDIN EN.CITE <EndNote><Cite><Author>Nguyen</Author><Year>2014</Year><RecNum>215</RecNum><DisplayText>83</DisplayText><record><rec-number>215</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>215</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nguyen, Ba Dung</author><author>Ngo, Trung Kien</author><author>Bui, Truong Han</author><author>Pham, Duy Khanh</author><author>Dinh, Xuan Loc</author><author>Nguyen, Phuong Tung</author></authors></contributors><titles><title>The impact of graphene oxide particles on viscosity stabilization for diluted polymer solutions using in enhanced oil recovery at HTHP offshore reservoirs</title><secondary-title>Advances in Natural Sciences: Nanoscience and Nanotechnology</secondary-title></titles><periodical><full-title>Advances in Natural Sciences: Nanoscience and Nanotechnology</full-title></periodical><pages>015012</pages><volume>6</volume><number>1</number><dates><year>2014</year></dates><isbn>2043-6262</isbn><urls></urls></record></Cite></EndNote>83, This showed that GOs is a potential agent for enhancing oil recovery. Nanofluids of graphene-based amphiphilic Janus nanosheets were also used at low concentration, additional oil recovery was recovered due to interfacial tension reduction ADDIN EN.CITE <EndNote><Cite><Author>Luo</Author><Year>2016</Year><RecNum>216</RecNum><DisplayText>84</DisplayText><record><rec-number>216</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>216</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Luo, Dan</author><author>Wang, Feng</author><author>Zhu, Jingyi</author><author>Cao, Feng</author><author>Liu, Yuan</author><author>Li, Xiaogang</author><author>Willson, Richard C</author><author>Yang, Zhaozhong</author><author>Chu, Ching-Wu</author><author>Ren, Zhifeng</author></authors></contributors><titles><title>Nanofluid of graphene-based amphiphilic Janus nanosheets for tertiary or enhanced oil recovery: High performance at low concentration</title><secondary-title>Proceedings of the National Academy of Sciences</secondary-title></titles><periodical><full-title>Proceedings of the National Academy of Sciences</full-title></periodical><pages>201608135</pages><dates><year>2016</year></dates><isbn>0027-8424</isbn><urls></urls></record></Cite></EndNote>84. Graphene oxide (GO), nanographene oxide (nGO) and partially reduced graphene oxide (rGO) were also studied as possible foam stabilizing agents for CO2 based enhanced oil recovery ADDIN EN.CITE <EndNote><Cite><Author>Barrabino</Author><Year>2018</Year><RecNum>232</RecNum><DisplayText>85</DisplayText><record><rec-number>232</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>232</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Barrabino, Albert</author><author>Holt, Torleif</author><author>Lindeberg, Erik</author></authors></contributors><titles><title>Graphene Oxide as Foam Stabilizing Agent for CO2 EOR</title></titles><dates><year>2018</year></dates><urls></urls></record></Cite></EndNote>85. Notwithstanding their recent reported potential and ability to enhance oil recovery, however, most studies have been performed at ambient conditions and fewer studies have been performed with graphene in both sandstone and carbonates. Therefore, further surveys are still required to understand a clear mechanism under which graphene may enhance oil recovery, especially at reservoir conditions. The highlights of some of the studies that have been performed using GO NPs to enhance oil recovery can be found in Table 1 attached.

2.8. Carbon nanotubes (CNT)
Carbon nanotubes are tube-shaped material, made of carbon, having a diameter measuring on the nanometer scale. CNT is unique because the bonding between the atoms is very strong and the tubes can have extreme aspect ratios. These types of nanomaterials are light, strong, resistant to corrosion, good conductors of heat, and have a very large surface area ADDIN EN.CITE <EndNote><Cite><Author>Wasan</Author><Year>2003</Year><RecNum>178</RecNum><DisplayText>86</DisplayText><record><rec-number>178</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>178</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wasan, Darsh T</author><author>Nikolov, Alex D</author></authors></contributors><titles><title>Spreading of nanofluids on solids</title><secondary-title>Nature</secondary-title></titles><periodical><full-title>Nature</full-title></periodical><pages>156</pages><volume>423</volume><number>6936</number><dates><year>2003</year></dates><isbn>0028-0836</isbn><urls></urls></record></Cite></EndNote>86. These nanotubes can be single, double or multi-walled and each wall is made of graphene. CNT exhibit astonishing properties due to the formation of the three sp2 hybridized bond and presence of extra electron from each carbon atom, making these nanomaterials potential materials for electrical, thermal conductivity and mechanical applications. The use of carbon nanotubes for enhancing oil recovery has been recently reported. Mohamed et al. ADDIN EN.CITE <EndNote><Cite><Author>Alnarabiji</Author><Year>2016</Year><RecNum>240</RecNum><DisplayText>87</DisplayText><record><rec-number>240</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>240</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Alnarabiji, Mohamad Sahban</author><author>Yahya, Noorhana</author><author>Shafie, Afza</author><author>Solemani, Hassan</author><author>Chandran, Kayathiri</author><author>Hamid, Sharifah Bee Abd</author><author>Azizi, Khairun</author></authors></contributors><titles><title>The influence of hydrophobic multiwall carbon nanotubes concentration on enhanced oil recovery</title><secondary-title>Procedia engineering</secondary-title></titles><periodical><full-title>Procedia engineering</full-title></periodical><pages>1137-1140</pages><volume>148</volume><dates><year>2016</year></dates><isbn>1877-7058</isbn><urls></urls></record></Cite></EndNote>87 examined the impact of multi-wall carbon nanotubes (MWCNTs) concentration on oil recovery efficiency and fluid mobility. The authors used nanofluids of three different concentrations: 0.01, 0.05 and 0.10 wt. %. A water flooding experiment was then carried out to assess the impact of these nanofluids. Results showed that the MWCNTs fluid was good EOR agents. The highest recovery efficiency of 31.8% of residual oil in place (ROIP) was achieved with the 0.05 wt % MWCNTs concentration. However, by observing the values of the mobility reduction factor (MRF) used to investigate the fluid behaviour, the researchers concluded that the behaviour of hydrophobic MWCNTs in water fluid was unpredictable. To the best of our knowledge, however, there has been little research about the use of these types of nanoparticles for improving oil recovery, and further investigations are still required especially at reservoir conditions. The highlights of some of the studies that have been performed to enhance oil recovery with CNT NPs can be found in Table 1 attached.

2.9 Cellulose nanoparticles
Cellulose is considered the most abundant, renewable, and sustainable biopolymer on earth. It is found in plants, tunicates, and some bacteria. Many distinctive chemical and physical properties such as strength, the large surface area can be enhanced when cellulose is used at the nanoscale. Its application in enhancing oil recovery has been reported. Bing et al ADDIN EN.CITE <EndNote><Cite><Author>Wei</Author><Year>2016</Year><RecNum>97</RecNum><DisplayText>88</DisplayText><record><rec-number>97</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>97</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wei, Bing</author><author>Li, Qinzhi</author><author>Jin, Fayang</author><author>Li, Hao</author><author>Wang, Chongyang</author></authors></contributors><titles><title>The potential of a novel nanofluid in enhancing oil recovery</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2882-2891</pages><volume>30</volume><number>4</number><dates><year>2016</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>88 injected nanocellulose fluid of different particle charge densities and mass fraction in a micro glass model. They found out that oil recovery was a function of both the particle charge density and concentration, two nanocellulose NC-1 and NC-2, with charge density 0.72 and 1.51 meq/q, respectively were used. The authors realized that NC-2 with higher particle charge was forming a homogenous nanofluid than NC-1 and in terms of IFT reduction, NC-2 performed better than NC-1 due to particle charge difference the viscosity loss of the nanocellulose was lower than the commonly used hydrolyzed polyacrylamide (HPAM) which is normally used in polymer flooding, they recommended nanocellulose as a potential candidate that can be used as polymer-surfactant materials to improve the macro and micro-displacement efficiency at low cost. The highlights of some of the studies that have been performed to enhance oil recovery using Cellulose NPs can be found in Table 1 attached.

3. Nanoparticle stabilization for EOR applicationNanoparticles are categorised as particles with various shape, sizes, particle crystallinity, surface area, and chemical composition ADDIN EN.CITE <EndNote><Cite><Author>Donaldson</Author><Year>2001</Year><RecNum>263</RecNum><DisplayText>89</DisplayText><record><rec-number>263</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>263</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Donaldson, Kenneth</author><author>Stone, Vicky</author><author>Clouter, Anna</author><author>Renwick, Louise</author><author>MacNee, William</author></authors></contributors><titles><title>Ultrafine particles</title><secondary-title>Occupational and environmental medicine</secondary-title></titles><periodical><full-title>Occupational and environmental medicine</full-title></periodical><pages>211-216</pages><volume>58</volume><number>3</number><dates><year>2001</year></dates><isbn>1351-0711</isbn><urls></urls></record></Cite></EndNote>89. As the particle dimension decrease, the number of surface molecules exponentially increases resulting in a higher surface area of nanoparticles compared to the bulk material. Nanomaterial can show hydrophilic, hydrophobic or double-faced (Janus) characteristics depending on their application, surface ligands, stabilizers and polymer/surfactants used ADDIN EN.CITE <EndNote><Cite><Author>Singh</Author><Year>2015</Year><RecNum>264</RecNum><DisplayText>90</DisplayText><record><rec-number>264</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>264</key></foreign-keys><ref-type name=”Book”>6</ref-type><contributors><authors><author>Singh, Ashok K</author></authors></contributors><titles><title>Engineered nanoparticles: structure, properties and mechanisms of toxicity</title></titles><dates><year>2015</year></dates><publisher>Academic Press</publisher><isbn>012801492X</isbn><urls></urls></record></Cite></EndNote>90. Nanoparticles for EOR applications in most cases are dispersed in fluids such as oil, deionized water, brine or gas to formulate nanofluids. However, in most cases because of their sizes, they are not stable and tend to aggregate and form sediments that minimize their dispersity ADDIN EN.CITE <EndNote><Cite><Author>Saidur</Author><Year>2011</Year><RecNum>144</RecNum><DisplayText>91</DisplayText><record><rec-number>144</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>144</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Saidur, R</author><author>Leong, KY</author><author>Mohammad, HaA</author></authors></contributors><titles><title>A review on applications and challenges of nanofluids</title><secondary-title>Renewable and sustainable energy reviews</secondary-title></titles><periodical><full-title>Renewable and Sustainable Energy Reviews</full-title></periodical><pages>1646-1668</pages><volume>15</volume><number>3</number><dates><year>2011</year></dates><isbn>1364-0321</isbn><urls></urls></record></Cite></EndNote>91. Due to this aggregation and precipitation, large particles with non-uniform size distribution tend to form clusters, creating practical challenges and limitations for oil field applications ADDIN EN.CITE <EndNote><Cite><Author>Hashemi</Author><Year>2014</Year><RecNum>93</RecNum><DisplayText>40, 57</DisplayText><record><rec-number>93</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525934498″>93</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hashemi, Rohallah</author><author>Nassar, Nashaat N</author><author>Almao, Pedro Pereira</author></authors></contributors><titles><title>Nanoparticle technology for heavy oil in-situ upgrading and recovery enhancement: Opportunities and challenges</title><secondary-title>Applied Energy</secondary-title></titles><periodical><full-title>Applied Energy</full-title></periodical><pages>374-387</pages><volume>133</volume><dates><year>2014</year></dates><isbn>0306-2619</isbn><urls></urls></record></Cite><Cite><Author>Hendraningrat</Author><Year>2015</Year><RecNum>150</RecNum><record><rec-number>150</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>150</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hendraningrat, Luky</author><author>Torsæter, Ole</author></authors></contributors><titles><title>Metal oxide-based nanoparticles: revealing their potential to enhance oil recovery in different wettability systems</title><secondary-title>Applied Nanoscience</secondary-title></titles><periodical><full-title>Applied Nanoscience</full-title></periodical><pages>181-199</pages><volume>5</volume><number>2</number><dates><year>2015</year></dates><isbn>2190-5509</isbn><urls></urls></record></Cite></EndNote>40, 57. Accordingly, particle size and size distribution need to be closely monitored to avoid aggregation that may limit the aggregation of the nanoparticles. Nanoparticle stabilization involves numerous procedures that have been proposed prior to their application in EOR. These include ultrasonication, steric, and electrostatic stabilization ADDIN EN.CITE <EndNote><Cite><Author>Jiang</Author><Year>2009</Year><RecNum>268</RecNum><DisplayText>92</DisplayText><record><rec-number>268</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>268</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Jiang, Jingkun</author><author>Oberdörster, Günter</author><author>Biswas, Pratim</author></authors></contributors><titles><title>Characterization of size, surface charge, and agglomeration state of nanoparticle dispersions for toxicological studies</title><secondary-title>Journal of Nanoparticle Research</secondary-title></titles><periodical><full-title>Journal of Nanoparticle Research</full-title></periodical><pages>77-89</pages><volume>11</volume><number>1</number><dates><year>2009</year></dates><isbn>1388-0764</isbn><urls></urls></record></Cite></EndNote>92. In the ultrasonic method, nano-size particles are dispersed into liquids, such as solvents, water, oil, or resins using an ultrasonic sonicator. The use of the ultrasonic method to stabilise nanomaterials has manifold benefits, the most obvious is the homogenous dispersion of the materials in the liquid preventing particles from agglomerating ADDIN EN.CITE <EndNote><Cite><Author>Ghadimi</Author><Year>2011</Year><RecNum>267</RecNum><DisplayText>93</DisplayText><record><rec-number>267</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>267</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Ghadimi, A</author><author>Saidur, R</author><author>Metselaar, HSC</author></authors></contributors><titles><title>A review of nanofluid stability properties and characterization in stationary conditions</title><secondary-title>International journal of heat and mass transfer</secondary-title></titles><periodical><full-title>International Journal of Heat and Mass Transfer</full-title></periodical><pages>4051-4068</pages><volume>54</volume><number>17-18</number><dates><year>2011</year></dates><isbn>0017-9310</isbn><urls></urls></record></Cite></EndNote>93.
Electrostatic stabilization of nanoparticles in a suspension is designated by the DLVO theory (Derjaguin, Landau, Verwey, and Overbeek). The interaction between two particles in a suspension is related to the combination of van der Waals attraction potential and the electric repulsion potential. However, electrostatic stabilization is limited by the following facts; this method is applicable to only dilute systems, it is a kinetic stabilization method, it is not applicable to electrolyte sensitive systems, it is almost not possible to disperse again the agglomerated particles, and since in a given condition, different solids develop different surface charge and electric potential, it is difficult to apply it in multiple phase systems.

Steric stabilization, also referred to as polymeric stabilization involves the addition of inhibitors such as surfactants with water-loving chains and water-loving polymers that prevent aggregation of nanoparticles in suspensions. The addition of polymers and surfactants helps to cover the system in such a way that long tails extend out into the solution. Sterically stabilized systems tend to remain well dispersed even at high salt concentrations or under circumstances where the zeta potential of the system is close to zero ADDIN EN.CITE <EndNote><Cite><Author>Tiraferri</Author><Year>2008</Year><RecNum>269</RecNum><DisplayText>94</DisplayText><record><rec-number>269</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>269</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Tiraferri, Alberto</author><author>Chen, Kai Loon</author><author>Sethi, Rajandrea</author><author>Elimelech, Menachem</author></authors></contributors><titles><title>Reduced aggregation and sedimentation of zero-valent iron nanoparticles in the presence of guar gum</title><secondary-title>Journal of Colloid and Interface Science</secondary-title></titles><periodical><full-title>Journal of colloid and interface science</full-title></periodical><pages>71-79</pages><volume>324</volume><number>1-2</number><dates><year>2008</year></dates><isbn>0021-9797</isbn><urls></urls></record></Cite></EndNote>94. Steric stabilization effectiveness is ascribed to the thermodynamic consequence when one tries to curb polymeric chains to lesser volumes ADDIN EN.CITE <EndNote><Cite><Author>Napper</Author><Year>1977</Year><RecNum>270</RecNum><DisplayText>95</DisplayText><record><rec-number>270</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>270</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Napper, Donald H</author></authors></contributors><titles><title>Steric stabilization</title><secondary-title>Journal of Colloid and Interface Science</secondary-title></titles><periodical><full-title>Journal of colloid and interface science</full-title></periodical><pages>390-407</pages><volume>58</volume><number>2</number><dates><year>1977</year></dates><isbn>0021-9797</isbn><urls></urls></record></Cite></EndNote>95. Steric stabilization offers advantages over the electrostatic stabilization method, particles are always re-dispersible since it is a thermodynamic method, with this method, a very high concentration can be accommodated, it is not sensitive to electrolytes, and it is suitable to multiple phase systems. Electrostatic stabilization can also be combined with steric stabilization which is denoted as electrosteric stabilization. This is achieved by attaching polymers/surfactants to a charged particle surface and hence developing a polymer or surfactant in such situations when two particles approach each other, both steric and electrostatic repulsion prevent agglomeration. 

Figure SEQ figure. * ARABIC 2. Electrostatic and steric stabilization.

4. Mechanisms of enhancing oil recovery using nanoparticles
Different mechanisms have been reported recently by different researchers using nanoparticles as nanofluids, nanoemulsions or nanocatalysts as described below:
4.1. Wettability alterations and contact angle
Wettability plays an important role in the oil recovery process and reservoir productivity ADDIN EN.CITE <EndNote><Cite><Author>Farad</Author><Year>2016</Year><RecNum>120</RecNum><DisplayText>17, 96</DisplayText><record><rec-number>120</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>120</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Farad, Sagala</author><author>Mugisa, John</author><author>Alahdal, Hussein A</author><author>Idris, Ahmad Kamal</author><author>Kisiki, Nsamba Hussein</author><author>Kabenge, Isa</author></authors></contributors><titles><title>Effect of wettability on oil recovery and breakthrough time for immiscible gas flooding</title><secondary-title>Petroleum Science and Technology</secondary-title></titles><periodical><full-title>Petroleum Science and Technology</full-title></periodical><pages>1705-1711</pages><volume>34</volume><number>20</number><dates><year>2016</year></dates><isbn>1091-6466</isbn><urls></urls></record></Cite><Cite><Author>Giraldo</Author><Year>2013</Year><RecNum>67</RecNum><record><rec-number>67</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1524695725″>67</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Giraldo, Juliana</author><author>Benjumea, Pedro</author><author>Lopera, Sergio</author><author>Corte?s, Farid B</author><author>Ruiz, Marco A</author></authors></contributors><titles><title>Wettability alteration of sandstone cores by alumina-based nanofluids</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3659-3665</pages><volume>27</volume><number>7</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>17, 96. It is one of the fundamental factors controlling the fluid flow and distribution in porous media. Regardless of the mineral composition of the reservoir rocks, most reservoirs are considered to have mixed wettability; that is, they are neither completely wetted by oil or water ADDIN EN.CITE <EndNote><Cite><Author>Giraldo</Author><Year>2013</Year><RecNum>67</RecNum><DisplayText>17</DisplayText><record><rec-number>67</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1524695725″>67</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Giraldo, Juliana</author><author>Benjumea, Pedro</author><author>Lopera, Sergio</author><author>Corte?s, Farid B</author><author>Ruiz, Marco A</author></authors></contributors><titles><title>Wettability alteration of sandstone cores by alumina-based nanofluids</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3659-3665</pages><volume>27</volume><number>7</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>17. During oil recovery, altering the reservoir to water-wet is preferred because it accelerates the spontaneous imbibition of water into the rock matrix blocks, which results in improved oil recovery especially during waterflooding ADDIN EN.CITE <EndNote><Cite><Author>Salehi</Author><Year>2008</Year><RecNum>152</RecNum><DisplayText>97</DisplayText><record><rec-number>152</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>152</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Salehi, Mehdi</author><author>Johnson, Stephen J</author><author>Liang, Jenn-Tai</author></authors></contributors><titles><title>Mechanistic study of wettability alteration using surfactants with applications in naturally fractured reservoirs</title><secondary-title>Langmuir</secondary-title></titles><periodical><full-title>Langmuir</full-title></periodical><pages>14099-14107</pages><volume>24</volume><number>24</number><dates><year>2008</year></dates><isbn>0743-7463</isbn><urls></urls></record></Cite></EndNote>97. Due to rock and fluid interaction, however, there always exists a change from water-wet to oil-wet at different stages of the producing life of a reservoir. Wettability alteration can be caused by various activities. For example, during drilling, the drilling fluids such as oil-based mud can alter the wettability of the system to oil-wet or mixed-wet ADDIN EN.CITE <EndNote><Cite><Author>Yan</Author><Year>1993</Year><RecNum>150</RecNum><DisplayText>98</DisplayText><record><rec-number>150</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>150</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Yan, JN</author><author>Monezes, JL</author><author>Sharma, Mukul M</author></authors></contributors><titles><title>Wettability alteration caused by oil-based muds and mud components</title><secondary-title>SPE drilling &amp; completion</secondary-title></titles><periodical><full-title>SPE drilling &amp; completion</full-title></periodical><pages>35-44</pages><volume>8</volume><number>01</number><dates><year>1993</year></dates><isbn>1064-6671</isbn><urls></urls></record></Cite></EndNote>98. This occurs because the ionic interactions and surface precipitation of these drilling fluids may precipitate at the surface in presence of water and result in new wetting preference ADDIN EN.CITE <EndNote><Cite><Author>Al-Maamari</Author><Year>2003</Year><RecNum>31</RecNum><DisplayText>99</DisplayText><record><rec-number>31</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1524515842″>31</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Al-Maamari, Rashid SH</author><author>Buckley, Jill S</author></authors></contributors><titles><title>Asphaltene precipitation and alteration of wetting: the potential for wettability changes during oil production</title><secondary-title>SPE Reservoir Evaluation &amp; Engineering</secondary-title></titles><periodical><full-title>SPE Reservoir Evaluation &amp; Engineering</full-title></periodical><pages>210-214</pages><volume>6</volume><number>04</number><dates><year>2003</year></dates><isbn>1094-6470</isbn><urls></urls></record></Cite></EndNote>99. Contact angle measurement is the common technique used to determine the wettability of the rock. This is defined as the angle, conventionally measured through the liquid, where a liquid or a vapour interface meets a solid surface. A surface is said to be water-wet if the contact angle is <900, or oil-wet if the contact angle is >900 ADDIN EN.CITE <EndNote><Cite><Author>ShamsiJazeyi</Author><Year>2014</Year><RecNum>45</RecNum><DisplayText>100</DisplayText><record><rec-number>45</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>45</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>ShamsiJazeyi, Hadi</author><author>Miller, Clarence A</author><author>Wong, Michael S</author><author>Tour, James M</author><author>Verduzco, Rafael</author></authors></contributors><titles><title>Polymer?coated nanoparticles for enhanced oil recovery</title><secondary-title>Journal of Applied Polymer Science</secondary-title></titles><periodical><full-title>Journal of Applied Polymer Science</full-title></periodical><volume>131</volume><number>15</number><dates><year>2014</year></dates><isbn>1097-4628</isbn><urls></urls></record></Cite></EndNote>100. The spreading coefficient S of water on a solid in contact with both oil and water can be defined in terms of the interfacial tension between each phase:
S=?O/S-?W/S-?O/W (1)
where ?O/S, ?W/S and ?O/W are the interfacial energies, between oil/solid, water/solid and oil/water, respectively. The contact angle formed largely depends on the force balance at the interface, reducing the interfacial tension at the water-oil interface, results in increased S which reduces the contact angle which results into a water-wet system ADDIN EN.CITE <EndNote><Cite><Author>ShamsiJazeyi</Author><Year>2014</Year><RecNum>45</RecNum><DisplayText>100</DisplayText><record><rec-number>45</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>45</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>ShamsiJazeyi, Hadi</author><author>Miller, Clarence A</author><author>Wong, Michael S</author><author>Tour, James M</author><author>Verduzco, Rafael</author></authors></contributors><titles><title>Polymer?coated nanoparticles for enhanced oil recovery</title><secondary-title>Journal of Applied Polymer Science</secondary-title></titles><periodical><full-title>Journal of Applied Polymer Science</full-title></periodical><volume>131</volume><number>15</number><dates><year>2014</year></dates><isbn>1097-4628</isbn><urls></urls></record></Cite></EndNote>100. Recently, evidence has shown that nanoparticles dispersed in various liquid agents can strongly alter the wettability of reservoir rocks from oil-wet to water-wet by changing the contact angle between the fluid and the rock. Munsihi et al ADDIN EN.CITE <EndNote><Cite><Author>Munshi</Author><Year>2008</Year><RecNum>133</RecNum><DisplayText>101</DisplayText><record><rec-number>133</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>133</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Munshi, AM</author><author>Singh, VN</author><author>Kumar, Mukesh</author><author>Singh, JP</author></authors></contributors><titles><title>Effect of nanoparticle size on sessile droplet contact angle</title><secondary-title>Journal of Applied Physics</secondary-title></titles><periodical><full-title>Journal of Applied Physics</full-title></periodical><pages>084315</pages><volume>103</volume><number>8</number><dates><year>2008</year></dates><isbn>0021-8979</isbn><urls></urls></record></Cite></EndNote>101, investigated the variations in the macroscopic contact angle using different nanoparticles sizes. They used indium oxide (IO) nanoparticle coated Si substrates on two different fluids like deionized water and diethylene glycol (DEG) with different nanoparticle sizes. These IO nanoparticles had well-defined shapes and sizes, and they observed that the contact angle depends strongly on the nanoparticle sizes.
For the nanoparticle sizes varying from 14 to 620 nm, the contact angle was found to vary from 24° to 67° for the de-ionized water droplet and from 15° to 60° for DEG droplet. They concluded that the contact angle decreases with a decrease in the particle size for any given fluid. Moreover, adsorption of the nanoparticle on the rock surface may have an impact on the permeability impairment which can result in absolute permeability reduction and an increase in the relative permeability of the oil. Several studies have been conducted. Jianjia et al ADDIN EN.CITE <EndNote><Cite><Author>Yu</Author><Year>2012</Year><RecNum>142</RecNum><DisplayText>52</DisplayText><record><rec-number>142</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>142</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Yu, Jianjia</author><author>An, Cheng</author><author>Mo, Di</author><author>Liu, Ning</author><author>Lee, Robert L</author></authors></contributors><titles><title>Study of adsorption and transportation behavior of nanoparticles in three different porous media</title><secondary-title>SPE Improved Oil Recovery Symposium</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613991975</isbn><urls></urls></record></Cite></EndNote>52, studied the transport, retention and adsorption behaviour of nanoparticles in three different porous media: sandstone, limestone and dolomite. The results showed an equilibrium adsorption of 1.272 mg/g, 5.501 mg/g and 0 mg/respectively, obtained in less than 12 h for the three-porous media using 5000 ppm silica dispersion. They observed that silica nanoparticles could easily flow in the sandstone rock without changing the core permeability. However, adsorption was noticed during silica flooding in the limestone core, although no change in the permeability was observed. They attributed this to the electrostatic attractive forces between silica nanoparticles and limestone at the surface. High particle recovery was obtained using dolomite core, indicating less adsorption of the nanoparticles on the dolomite surface, however, they observed a pressure drop across the core which indicated nanoparticle plugging that might have resulted in a change in the permeability.

Surfactants have always been used as wettability modifiers; however, studies of nanoparticles combined with surfactants have reported better wettability alterations than using either nanoparticles or surfactant alone. Studies have been conducted to determine the synergistic effect of surfactant and nanoparticles for various nanoparticle types and nanoparticle sizes. Karim et al. ADDIN EN.CITE <EndNote><Cite><Author>Karimi</Author><Year>2012</Year><RecNum>141</RecNum><DisplayText>74</DisplayText><record><rec-number>141</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>141</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Karimi, Ali</author><author>Fakhroueian, Zahra</author><author>Bahramian, Alireza</author><author>Pour Khiabani, Nahid</author><author>Darabad, Jabar Babaee</author><author>Azin, Reza</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Wettability alteration in carbonates using zirconium oxide nanofluids: EOR implications</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1028-1036</pages><volume>26</volume><number>2</number><dates><year>2012</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>74 investigated the effect of using zirconium oxide (ZrO2) nanofluids in a carbonate reservoir to alter the wettability of a carbonate rock. Several nanofluids were made containing ZrO2 nanoparticles and a mixture of a non-ionic surfactant. Two nanoparticle concentrations (50000 ppm and 100000 ppm) were used for the test. The effect of wettability alteration of the injected nanofluids was determined by measuring the contact angle before and after treatment with the nanofluids. They found out that the designed nanofluids could significantly alter the wettability of the rock from a strong oil-wet to a strongly water-wet, resulting in additional oil recovery. Juliana et al ADDIN EN.CITE <EndNote><Cite><Author>Giraldo</Author><Year>2013</Year><RecNum>67</RecNum><DisplayText>17</DisplayText><record><rec-number>67</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1524695725″>67</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Giraldo, Juliana</author><author>Benjumea, Pedro</author><author>Lopera, Sergio</author><author>Corte?s, Farid B</author><author>Ruiz, Marco A</author></authors></contributors><titles><title>Wettability alteration of sandstone cores by alumina-based nanofluids</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3659-3665</pages><volume>27</volume><number>7</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>17, conducted a similar study but dispersed alumina-based nanofluids with different concentrations ranging from 100 ppm to 10000 ppm into an anionic commercial surfactant (PRNS). They also analyzed the effect of their resultant nano?uids on wettability alteration by measuring the contact angle and carrying out imbibition tests. They found out that designed nano?uids containing anionic surfactants could signi?cantly change the wettability of the sandstone cores from a strongly induced oil-wet to a strongly water-wet condition. It was concluded that the effectiveness of the anionic surfactant as wettability modi?er could be improved when combined with nanoparticles in concentrations lower or equal to 500 ppm because their best performance was achieved at a concentration of 100 ppm.
Rasoul et al ADDIN EN.CITE <EndNote><Cite><Author>Nazari Moghaddam</Author><Year>2015</Year><RecNum>52</RecNum><DisplayText>55</DisplayText><record><rec-number>52</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>52</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nazari Moghaddam, Rasoul</author><author>Bahramian, Alireza</author><author>Fakhroueian, Zahra</author><author>Karimi, Ali</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Comparative Study of Using Nanoparticles for Enhanced Oil Recovery: Wettability Alteration of Carbonate Rocks</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2111-2119</pages><volume>29</volume><number>4</number><dates><year>2015</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef5024719</electronic-resource-num></record></Cite></EndNote>55, compared the effect of different nanoparticles on altering the wettability of carbonate rocks. They compared zirconium dioxide (ZrO2), calcium carbonate (CaCO3), titanium dioxide (TiO2), silicon dioxide (siO2), magnesium oxide (MgO), aluminum oxide (Al2O3), cerium oxide (CeO2), and carbon nanotubes (CNT) on their ability to alter the wettability of carbonate rocks, the authors did a primary screening for the nanoparticles by contact angle measurements. The selected nanoparticles were subjected to core flooding and spontaneous imbibition experiments. The results from the core flooding and spontaneous imbibition experiment confirmed the active role of CaCO3 and SiO2 nanoparticles for enhancing oil recovery. The authors also examined the effect of the injected nanofluids on surface wettability by drainage capillary pressure measurements and it showed an increase in irreducible water saturation and entry capillary pressure after treatment with CaCO3 nanofluids.
4.2. Viscosity reduction
Oil viscosity reduction is essential during production processes. Generally, crude oil with a viscosity of less than 400 mPa s is the classical maximum desired pipeline viscosity ADDIN EN.CITE <EndNote><Cite><Author>Hasan</Author><Year>2010</Year><RecNum>144</RecNum><DisplayText>102</DisplayText><record><rec-number>144</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>144</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hasan, Shadi W</author><author>Ghannam, Mamdouh T</author><author>Esmail, Nabil</author></authors></contributors><titles><title>Heavy crude oil viscosity reduction and rheology for pipeline transportation</title><secondary-title>Fuel</secondary-title></titles><periodical><full-title>Fuel</full-title></periodical><pages>1095-1100</pages><volume>89</volume><number>5</number><dates><year>2010</year></dates><isbn>0016-2361</isbn><urls></urls></record></Cite></EndNote>102. However, in many situations, this is not the case and methods are being devised on how viscosity reduction can be achieved. Thermal recovery methods are commonly used for oil viscosity reduction ADDIN EN.CITE <EndNote><Cite><Author>Shu</Author><Year>1986</Year><RecNum>126</RecNum><DisplayText>12</DisplayText><record><rec-number>126</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>126</key></foreign-keys><ref-type name=”Generic”>13</ref-type><contributors><authors><author>Shu, Winston R</author><author>Hartman, Kathy J</author></authors></contributors><titles><title>Thermal recovery method for viscous oil</title></titles><dates><year>1986</year></dates><publisher>Google Patents</publisher><urls></urls></record></Cite></EndNote>12. Because of their heat transfer abilities, these methods have been improved by applying nanoparticles. In these processes, nanoparticles can act as catalysts for heat transfer. Researchers have investigated the use of nanoparticles in viscosity reduction and promising findings have been reported. Wei et al ADDIN EN.CITE <EndNote><Cite><Author>Li</Author><Year>2007</Year><RecNum>146</RecNum><DisplayText>103</DisplayText><record><rec-number>146</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>146</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Li, Wei</author><author>Zhu, Jian-hua</author><author>Qi, Jian-hua</author></authors></contributors><titles><title>Application of nano-nickel catalyst in the viscosity reduction of Liaohe extra-heavy oil by aqua-thermolysis</title><secondary-title>Journal of Fuel Chemistry and Technology</secondary-title></titles><periodical><full-title>Journal of Fuel Chemistry and Technology</full-title></periodical><pages>176-180</pages><volume>35</volume><number>2</number><dates><year>2007</year></dates><isbn>18725813</isbn><urls></urls><electronic-resource-num>10.1016/s1872-5813(07)60016-4</electronic-resource-num></record></Cite></EndNote>103, used a nano-nickel catalyst that was prepared in methylcyclohexane-water-n-octanol-AEO9 micro-emulsion system, for the viscosity reduction process of Liaohe extra-heavy oil by aquathermolysis. It was observed that the nano-nickel can catalyze the aquathermolysis reaction of extra-heavy oil at 280 °C. The experimental results demonstrated that compared with the original crude oil sample, the mean molecular weight of the upgraded sample decreased, the content of sulfur also changed from 0.45% to 0.23%, and the content of resin and asphaltenes was reduced to 15.83% and 15.33%, respectively. During the cooling process after the upgrading reaction, the w/o emulsion was formed in the presence of the surfactant AEO9, changing the viscosity of the original crude from 139800 mPa·s to 2400 mPa·s at 50 °C. This is approximately a 98.90% reduction by the synergetic effects of upgrading, emulsification and diluting, demonstrating the ability of the nickel catalyst to greatly lower the viscosity of the heavy crude oil and improve the oil recovery. Esteban et al ADDIN EN.CITE <EndNote><Cite><Author>Taborda</Author><Year>2016</Year><RecNum>156</RecNum><DisplayText>104</DisplayText><record><rec-number>156</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>156</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Taborda, Esteban A.</author><author>Franco, Camilo A.</author><author>Lopera, Sergio H.</author><author>Alvarado, Vladimir</author><author>Cortés, Farid B.</author></authors></contributors><titles><title>Effect of nanoparticles/nanofluids on the rheology of heavy crude oil and its mobility on porous media at reservoir conditions</title><secondary-title>Fuel</secondary-title></titles><periodical><full-title>Fuel</full-title></periodical><pages>222-232</pages><volume>184</volume><dates><year>2016</year></dates><isbn>00162361</isbn><urls></urls><electronic-resource-num>10.1016/j.fuel.2016.07.013</electronic-resource-num></record></Cite></EndNote>104 have also reported promising results using alumina, silica and acidic silica nanoparticles to reduce the viscosity of heavy crude oil (HO). The effect was evaluated through n-C7 asphaltene adsorption and aggregation tests using UV–vis spectrophotometry and dynamic light scattering. The researchers selected the acidic silica nanoparticles to prepare a water-based nano?uid at different concentrations in distilled water because it exhibited the highest asphaltene adsorption capability during the batch adsorption test. They added 2.0 wt% of a non-ionic surfactant to determine the effect of the surfactants in presence of the silica nanoparticle to reduce the oil viscosity. The shear rheological response was obtained as a function of nanoparticle concentration, temperature, and shear rate ranging from 0 to 100s-1. Experimental results indicated that increasing the concentration of nanoparticles in the mixture, up to 10,000 ppm, leads to a viscosity reduction of approximately 90% in comparison with the nanoparticle-free crude oil. The authors found that at higher concentration of nanoparticles, the effectiveness of the heavy oil viscosity reduction diminishes as noted in an earlier study by the same authors ADDIN EN.CITE <EndNote><Cite><Author>Taborda</Author><Year>2017</Year><RecNum>147</RecNum><DisplayText>68</DisplayText><record><rec-number>147</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>147</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Taborda, Esteban A.</author><author>Franco, Camilo A.</author><author>Ruiz, Marco A.</author><author>Alvarado, Vladimir</author><author>Cortés, Farid B.</author></authors></contributors><titles><title>Experimental and Theoretical Study of Viscosity Reduction in Heavy Crude Oils by Addition of Nanoparticles</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1329-1338</pages><volume>31</volume><number>2</number><dates><year>2017</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/acs.energyfuels.6b02686</electronic-resource-num></record></Cite></EndNote>68. The core ?ooding tests conducted under typical reservoir conditions of pore and overburden pressures of 2600 and 3600 psi, respectively, and at 360 K resulted in an additional 16% oil recovery after water flooding. They concluded that the reduction of viscosity is achieved by adsorption of the asphaltenes on the surfaces of the dispersed nanoparticles. This study demonstrated that because of a synergistic effect; nanoparticles dispersed in a carrier ?uid containing a surfactant were more effective than those that used surfactants alone.

Recently, the same authors Esteban et al ADDIN EN.CITE <EndNote><Cite><Author>Taborda</Author><Year>2017</Year><RecNum>147</RecNum><DisplayText>68</DisplayText><record><rec-number>147</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>147</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Taborda, Esteban A.</author><author>Franco, Camilo A.</author><author>Ruiz, Marco A.</author><author>Alvarado, Vladimir</author><author>Cortés, Farid B.</author></authors></contributors><titles><title>Experimental and Theoretical Study of Viscosity Reduction in Heavy Crude Oils by Addition of Nanoparticles</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1329-1338</pages><volume>31</volume><number>2</number><dates><year>2017</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/acs.energyfuels.6b02686</electronic-resource-num></record></Cite></EndNote>68 reported unexpected results while investigating the effect of viscosity reduction of heavy and extra-heavy crude oils. Using nanoparticles of different chemical nature, which consisted of SiO2, Fe3O4, and Al2O3, they observed a viscosity reduction in all cases evaluated. However, the maximum viscosity reduction of roughly 52% was obtained at a concentration of 1000 mg/L with 8 nm SiO2 nanoparticles and at shear rates below 10 s. The authors noted that particle size, concentration, and shear rate influenced viscosity reduction. Increasing the particle size had less effect on viscosity reduction, due to the increased packing factor of the bigger nano-sized particles that generate interaction and results in nanoparticle aggregation. Also, increasing the shear rate slightly decreased the viscosity due to change in the internal structure of fluids that resulted in viscosity reduction. They concluded that having an optimized concentration and particle size can significantly reduce the viscosity of heavy and extra crude oil which can improve the oil recovery mobility as seen in Figure 3. a & b, increasing the nanoparticle concentrations beyond the optimum results in viscosity increase instead of decreasing it.

Figure 3. A representation of how nanoparticle concentration affects the oil viscosity (a) and (b) is the effect of shear rate on viscosity for different volumes of nanoparticle ADDIN EN.CITE <EndNote><Cite><Author>Shokrlu</Author><Year>2014</Year><RecNum>192</RecNum><DisplayText>105, 106</DisplayText><record><rec-number>192</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>192</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Shokrlu, Yousef Hamedi</author><author>Babadagli, Tayfun</author></authors></contributors><titles><title>Viscosity reduction of heavy oil/bitumen using micro-and nano-metal particles during aqueous and non-aqueous thermal applications</title><secondary-title>Journal of Petroleum Science and Engineering</secondary-title></titles><periodical><full-title>Journal of Petroleum Science and Engineering</full-title></periodical><pages>210-220</pages><volume>119</volume><dates><year>2014</year></dates><isbn>0920-4105</isbn><urls></urls></record></Cite><Cite><Author>Duan</Author><Year>2011</Year><RecNum>193</RecNum><record><rec-number>193</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>193</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Duan, Fei</author><author>Kwek, Dingtian</author><author>Crivoi, Alexandru</author></authors></contributors><titles><title>Viscosity affected by nanoparticle aggregation in Al 2 O 3-water nanofluids</title><secondary-title>Nanoscale research letters</secondary-title></titles><periodical><full-title>Nanoscale research letters</full-title></periodical><pages>248</pages><volume>6</volume><number>1</number><dates><year>2011</year></dates><isbn>1556-276X</isbn><urls></urls></record></Cite></EndNote>105, 106 respectively.

4.3. Nanoparticles combined with polymer for enhanced oil recovery
Polymers are common chemical additives used in the recovery of heavy oil. Scientists have studied the microscopic sweep mechanism of polymer ?ooding in enhancing oil recovery ADDIN EN.CITE <EndNote><Cite><Author>Wever</Author><Year>2011</Year><RecNum>154</RecNum><DisplayText>107</DisplayText><record><rec-number>154</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>154</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wever, DAZ</author><author>Picchioni, F</author><author>Broekhuis, AA</author></authors></contributors><titles><title>Polymers for enhanced oil recovery: a paradigm for structure–property relationship in aqueous solution</title><secondary-title>Progress in Polymer Science</secondary-title></titles><periodical><full-title>Progress in Polymer Science</full-title></periodical><pages>1558-1628</pages><volume>36</volume><number>11</number><dates><year>2011</year></dates><isbn>0079-6700</isbn><urls></urls></record></Cite></EndNote>107. They have concluded that polymer increases the sweep ef?ciency mainly by decreasing water permeability and increasing the injected fluid viscosity. They are suitable for viscous oils because water?ood sweep ef?ciency is always low due to viscous ?ngering and permeability heterogeneity ADDIN EN.CITE <EndNote><Cite><Author>Wassmuth</Author><Year>2009</Year><RecNum>134</RecNum><DisplayText>108</DisplayText><record><rec-number>134</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>134</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wassmuth, FR</author><author>Green, K</author><author>Arnold, W</author><author>Cameron, N</author></authors></contributors><titles><title>Polymer flood application to improve heavy oil recovery at East Bodo</title><secondary-title>Journal of Canadian Petroleum Technology</secondary-title></titles><periodical><full-title>Journal of Canadian Petroleum Technology</full-title></periodical><pages>55-61</pages><volume>48</volume><number>02</number><dates><year>2009</year></dates><isbn>0021-9487</isbn><urls></urls></record></Cite></EndNote>108.

Synergistic studies of nanoparticles with polymers are emerging. Studies have been performed either by grafting polymer chains on nanoparticles surfaces or using optimized concentrations of nanoparticles to improve the rheology of the polymer-based fluids. Grafting polymers on the surface of the nanoparticle can drastically improve solubility and stability, and the resulting particles also have higher ability to stabilize foams and emulsions ADDIN EN.CITE <EndNote><Cite><Author>ShamsiJazeyi</Author><Year>2014</Year><RecNum>45</RecNum><DisplayText>100</DisplayText><record><rec-number>45</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>45</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>ShamsiJazeyi, Hadi</author><author>Miller, Clarence A</author><author>Wong, Michael S</author><author>Tour, James M</author><author>Verduzco, Rafael</author></authors></contributors><titles><title>Polymer?coated nanoparticles for enhanced oil recovery</title><secondary-title>Journal of Applied Polymer Science</secondary-title></titles><periodical><full-title>Journal of Applied Polymer Science</full-title></periodical><volume>131</volume><number>15</number><dates><year>2014</year></dates><isbn>1097-4628</isbn><urls></urls></record></Cite></EndNote>100. Using nanomaterials in enhancing recovery can improve oil recovery compared to the conventional polymers without nanoparticles.

Nanofluids containing polyacrylamide clay were investigated in a polymer flooding study for enhancing heavy oil recovery. In their study, the authors focused on the roles of clay nanoparticles on polymer viscosity and their effect on improving oil recovery for a heavy oil of about 200 cp. Results from the core floods showed that nanopolymer fluids could decrease the oil recovery in comparison to a baseline polymer flood without nanoparticles. After one pore volume fluid injection, the flooding test showed a 5% increment of oil with the nanoclay polymer solution compared to a polymer solution without the nanoparticles ADDIN EN.CITE <EndNote><Cite><Author>Cheraghian</Author><Year>2015</Year><RecNum>155</RecNum><DisplayText>109</DisplayText><record><rec-number>155</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>155</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Cheraghian, G.</author><author>Khalilinezhad, S. S.</author></authors></contributors><titles><title>Effect of Nanoclay on Heavy Oil Recovery During Polymer Flooding</title><secondary-title>Petroleum Science and Technology</secondary-title></titles><periodical><full-title>Petroleum Science and Technology</full-title></periodical><pages>999-1007</pages><volume>33</volume><number>9</number><dates><year>2015</year></dates><isbn>1091-6466 1532-2459</isbn><urls></urls><electronic-resource-num>10.1080/10916466.2015.1014962</electronic-resource-num></record></Cite></EndNote>109.
Although studies have been performed to improve the application of PNPs in enhanced recoveries, more research of this application is still required. Because they are economical, they hold promise in enhancing oil recovery, but for proper usage, they also need to remain stable in harsh conditions and at high salinities. Therefore studies about the maximum duration of chemical stability and minimum adsorption on the rock still need to be conducted ADDIN EN.CITE <EndNote><Cite><Author>ShamsiJazeyi</Author><Year>2014</Year><RecNum>45</RecNum><DisplayText>100</DisplayText><record><rec-number>45</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>45</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>ShamsiJazeyi, Hadi</author><author>Miller, Clarence A</author><author>Wong, Michael S</author><author>Tour, James M</author><author>Verduzco, Rafael</author></authors></contributors><titles><title>Polymer?coated nanoparticles for enhanced oil recovery</title><secondary-title>Journal of Applied Polymer Science</secondary-title></titles><periodical><full-title>Journal of Applied Polymer Science</full-title></periodical><volume>131</volume><number>15</number><dates><year>2014</year></dates><isbn>1097-4628</isbn><urls></urls></record></Cite></EndNote>100.
4.4. Nano-based surfactant for enhanced oil recovery
These are closely related to nanopolymer, as they are also created by either grafting the surfactants together with a nanoparticle through electrostatic interactions or by synergising optimized concentrations of nanoparticles and surfactants. When surfactants are coated with nanoparticles, they form a monolayer on the surface of the nanoparticle which results in more hydrophobic particles that can be used to form stable foam and emulsions compared to using a surfactant or nanoparticles alone. This process depends on the concentration, sizes of the nanoparticles, and the surfactant type and concentrations used in the formulation ADDIN EN.CITE <EndNote><Cite><Author>Sun</Author><Year>2014</Year><RecNum>53</RecNum><DisplayText>110</DisplayText><record><rec-number>53</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>53</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Sun, Qian</author><author>Li, Zhaomin</author><author>Li, Songyan</author><author>Jiang, Lei</author><author>Wang, Jiqian</author><author>Wang, Peng</author></authors></contributors><titles><title>Utilization of Surfactant-Stabilized Foam for Enhanced Oil Recovery by Adding Nanoparticles</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2384-2394</pages><volume>28</volume><number>4</number><dates><year>2014</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef402453b</electronic-resource-num></record></Cite></EndNote>110. Studies of nanobased surfactants in enhancing oil recovery have been applied extensively in foam and emulsion stabilization PEVuZE5vdGU+PENpdGU+PEF1dGhvcj5MaXU8L0F1dGhvcj48WWVhcj4xOTk2PC9ZZWFyPjxSZWNO
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ADDIN EN.CITE.DATA 111-113. Researchers have recommended different surfactants types for various applications, mainly based on the rock mineralogy composition and the properties of a given reservoir. Poor selection of a surfactant can result in undesirable wettability alterations that can affect the overall oil recovery. An extensive review of EOR suggests that anionic surfactants are preferred for sandstone reservoirs, though in specific situations, cationic, non-ionic or mixtures of both have occasionally been used. For carbonate reservoirs, cationic surfactants or mixtures of them with non-ionic surfactants are preferred ADDIN EN.CITE <EndNote><Cite><Author>Negin</Author><Year>2017</Year><RecNum>223</RecNum><DisplayText>114</DisplayText><record><rec-number>223</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>223</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Negin, Chegenizadeh</author><author>Ali, Saeedi</author><author>Xie, Quan</author></authors></contributors><titles><title>Most common surfactants employed in chemical enhanced oil recovery</title><secondary-title>Petroleum</secondary-title></titles><periodical><full-title>Petroleum</full-title></periodical><pages>197-211</pages><volume>3</volume><number>2</number><dates><year>2017</year></dates><isbn>2405-6561</isbn><urls></urls></record></Cite></EndNote>114.

4.5. Application of nano stabilized foams for enhancing oil recovery
Foam is used for mobility control in gas flooding, and surfactants of varying concentrations have typically been used to stabilize this foam ADDIN EN.CITE <EndNote><Cite><Author>Heller</Author><Year>1994</Year><RecNum>128</RecNum><DisplayText>115</DisplayText><record><rec-number>128</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>128</key></foreign-keys><ref-type name=”Book Section”>5</ref-type><contributors><authors><author>Heller, John P</author></authors></contributors><titles><title>CO2 foams in enhanced oil recovery</title></titles><dates><year>1994</year></dates><publisher>ACS Publications</publisher><urls></urls></record></Cite></EndNote>115. Stabilization of foams with nanoparticles has attracted some attention from researchers PEVuZE5vdGU+PENpdGU+PEF1dGhvcj5ZdTwvQXV0aG9yPjxZZWFyPjIwMTI8L1llYXI+PFJlY051
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ADDIN EN.CITE.DATA 37, 116-118. Adoption of nanoparticles at the interface of water and gas requires more energy which makes the resulting foams very stable even at high temperatures for longer periods ADDIN EN.CITE <EndNote><Cite><Author>Espinoza</Author><Year>2010</Year><RecNum>129</RecNum><DisplayText>119</DisplayText><record><rec-number>129</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>129</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Espinoza, David Alejandro</author><author>Caldelas, Federico Manuel</author><author>Johnston, Keith P</author><author>Bryant, Steven Lawrence</author><author>Huh, Chun</author></authors></contributors><titles><title>Nanoparticle-stabilized supercritical CO2 foams for potential mobility control applications</title><secondary-title>SPE Improved Oil Recovery Symposium</secondary-title></titles><dates><year>2010</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1555632890</isbn><urls></urls></record></Cite></EndNote>119. Stable supercritical carbon dioxide (CO2) in water foams using 5 nm silica nanoparticles was generated using nanoparticles. The surface of the nanoparticles was functionalized with short chain polyethene glycol to form non-ionic surfactants that were used to improve the water-CO2 interaction and enhance the foam stability. The authors noticed that at low concentration of 0.05wt% of nanoparticles, stabilized forms could still be formed even at slightly higher temperatures of 95 0C. However, they concluded that larger particle sizes are required for enhanced foam stability at higher salinities ADDIN EN.CITE <EndNote><Cite><Author>Espinoza</Author><Year>2010</Year><RecNum>129</RecNum><DisplayText>119</DisplayText><record><rec-number>129</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>129</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Espinoza, David Alejandro</author><author>Caldelas, Federico Manuel</author><author>Johnston, Keith P</author><author>Bryant, Steven Lawrence</author><author>Huh, Chun</author></authors></contributors><titles><title>Nanoparticle-stabilized supercritical CO2 foams for potential mobility control applications</title><secondary-title>SPE Improved Oil Recovery Symposium</secondary-title></titles><dates><year>2010</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1555632890</isbn><urls></urls></record></Cite></EndNote>119. It should be noted that this study focused on the application of silica nanoparticle only, other researchers have further investigated the effect of nanoparticle types and size on foam stability. Manan et al., examined the performance of silicon dioxide (SiO2), aluminium oxide (Al2O3), copper oxide (CuO), and titanium dioxide (TiO2) of different sizes in the presence of a fixed concentration of anionic surfactant (AOS) on foam stability. Nanoparticle concentrations 0.1 wt%, 0.3 wt%, 0.5 wt%, and 1 wt% were used to investigate the foam stability. Displacement tests were performed to determine the oil recovery at the optimum concentrations for each nanoparticle at room temperature and pressure. Results revealed that all different nanoparticles used could improve the stability of CO2 foam at certain concentrations. Aluminium oxide nanoparticles, however, offered a better foam stability compared to other types ADDIN EN.CITE <EndNote><Cite><Author>Manan</Author><Year>2015</Year><RecNum>131</RecNum><DisplayText>120</DisplayText><record><rec-number>131</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>131</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Manan, M. A.</author><author>Farad, S.</author><author>Piroozian, A.</author><author>Esmail, M. J. A.</author></authors></contributors><titles><title>Effects of Nanoparticle Types on Carbon Dioxide Foam Flooding in Enhanced Oil Recovery</title><secondary-title>Petroleum Science and Technology</secondary-title></titles><periodical><full-title>Petroleum Science and Technology</full-title></periodical><pages>1286-1294</pages><volume>33</volume><number>12</number><dates><year>2015</year></dates><isbn>1091-6466 1532-2459</isbn><urls></urls><electronic-resource-num>10.1080/10916466.2015.1057593</electronic-resource-num></record></Cite></EndNote>120. This contrasts with what has been reported by David et al. ADDIN EN.CITE <EndNote><Cite><Author>Wasan</Author><Year>2011</Year><RecNum>59</RecNum><DisplayText>37</DisplayText><record><rec-number>59</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>59</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wasan, Darsh</author><author>Nikolov, Alex</author><author>Kondiparty, Kirti</author></authors></contributors><titles><title>The wetting and spreading of nanofluids on solids: Role of the structural disjoining pressure</title><secondary-title>Current Opinion in Colloid &amp; Interface Science</secondary-title></titles><periodical><full-title>Current Opinion in Colloid &amp; Interface Science</full-title></periodical><pages>344-349</pages><volume>16</volume><number>4</number><dates><year>2011</year></dates><isbn>1359-0294</isbn><urls></urls></record></Cite></EndNote>37 who confirmed that silica nanoparticles were more effective in stabilizing foams. Recently, Songyan et al. ADDIN EN.CITE <EndNote><Cite><Author>Li</Author><Year>2017</Year><RecNum>143</RecNum><DisplayText>121</DisplayText><record><rec-number>143</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>143</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Li, Songyan</author><author>Qiao, Chenyu</author><author>Li, Zhaomin</author><author>Wanambwa, Silagi</author></authors></contributors><titles><title>Properties of Carbon Dioxide Foam Stabilized by Hydrophilic Nanoparticles and Hexadecyltrimethylammonium Bromide</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1478-1488</pages><volume>31</volume><number>2</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>121 investigated the synergistic effect of using hydrophilic SiO2 nanoparticles and hexadecyltrimethylammonium bromide (CTAB) on CO2 foam stability to improve oil recovery during CO2 ?ooding. CTAB/SiO2 was used in a concentration ratio of 0.02-0.07, with 0.033 representing the best concentration ratio. The authors found out that with the increase in the concentration ratio, the synergistic stabilization effect of CTAB/SiO2 dispersion ?rst increased and then decreased. In the monolayer adsorption stage (concentration ratio from 0.02 to 0.033), when the hydrophobicity of SiO2 nanoparticles increased with the concentration ratio, the nanoparticles were adsorbed on the gas-liquid interface and the stability of CO2 foam increased. However, for the double-layer adsorption stage (concentration from 0.033 to 0.07), the nanoparticles existed in the bulk phase and the stability of CO2 nanoparticles decreased. They concluded that CTAB/SiO2 dispersion stabilized CO2 foam via three mechanisms: decreasing the coarsening of CO2 bubbles, improving interfacial properties, and reducing liquid discharge. The authors recommended that CTAB/SiO2 foam can greatly improve oil recovery e?ciency compared to water ?ooding. Weipeng et al, ADDIN EN.CITE <EndNote><Cite><Author>Yang</Author><Year>2017</Year><RecNum>138</RecNum><DisplayText>122</DisplayText><record><rec-number>138</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>138</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Yang, Weipeng</author><author>Wang, Tengfei</author><author>Fan, Zexia</author><author>Miao, Qiang</author><author>Deng, Zhiyu</author><author>Zhu, Yuanyuan</author></authors></contributors><titles><title>Foams Stabilized by In Situ-Modified Nanoparticles and Anionic Surfactants for Enhanced Oil Recovery</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>4721-4730</pages><volume>31</volume><number>5</number><dates><year>2017</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/acs.energyfuels.6b03217</electronic-resource-num></record></Cite></EndNote>122 studied the effect of positively charged AlOOH nanoparticles via the adsorption of the anionic surfactant sodium dodecyl sulphate (SDS) by in-situ modi?cation on foam stability under different conditions. Changes in the zeta potential and adsorption isotherm of the AlOOH nanoparticles con?rmed the effectiveness of this modi?cation. The authors noted that the most stable foam was obtained with an SDS/AlOOH concentration ratio of 5:1, while further increase in the SDS concentration led to a decrease and subsequent increase in foam stability. They concluded that nanoparticles with partial hydrophobicity, positive or slightly negative charge and small aggregate size can be adsorbed tightly to foam surfaces and form compact networks in the foam’s ?lm, resulting in a stable foam. The SDS/AlOOH-stabilized foam also showed good stability under high temperatures and in the presence of oil. They also noticed that SDS/AlOOH -stabilized foams strongly enhanced oil recovery due to their ability to remain stable even in harsh conditions. Qian Sun et al ADDIN EN.CITE ;EndNote;;Cite;;Author;Sun;/Author;;Year;2014;/Year;;RecNum;53;/RecNum;;DisplayText;110;/DisplayText;;record;;rec-number;53;/rec-number;;foreign-keys;;key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″;53;/key;;key app=”ENWeb” db-id=””;0;/key;;/foreign-keys;;ref-type name=”Journal Article”;17;/ref-type;;contributors;;authors;;author;Sun, Qian;/author;;author;Li, Zhaomin;/author;;author;Li, Songyan;/author;;author;Jiang, Lei;/author;;author;Wang, Jiqian;/author;;author;Wang, Peng;/author;;/authors;;/contributors;;titles;;title;Utilization of Surfactant-Stabilized Foam for Enhanced Oil Recovery by Adding Nanoparticles;/title;;secondary-title;Energy ;amp; Fuels;/secondary-title;;/titles;;periodical;;full-title;Energy ;amp; Fuels;/full-title;;/periodical;;pages;2384-2394;/pages;;volume;28;/volume;;number;4;/number;;dates;;year;2014;/year;;/dates;;isbn;0887-0624 1520-5029;/isbn;;urls;;/urls;;electronic-resource-num;10.1021/ef402453b;/electronic-resource-num;;/record;;/Cite;;/EndNote;110, conducted a similar study, but they used partially hydrophobic modi?ed SiO2 nanoparticles with the same anionic surfactant, sodium dodecyl sulphate (SDS), to increase foam stability. The authors used a micro model and a sand pack to assess the stability of the SiO2 stabilized foam (SiO2/SDS foam) on enhancing oil recovery. The experimental data showed that the foam stability decreased with an increase in temperature. SiO2/SDS foam showed better temperature tolerance than the SDS foam (foam stabilized by SDS) due to the adsorption of nanoparticles on the surface of the bubble. Almost all the bubbles maintained spherical or ellipsoidal shape over prolonged periods due to the enhanced surface dilutional viscoelasticity, which was different from that of SDS foam. The micro model ?ooding results demonstrated that SiO2/SDS foam displaced more oil than brine ?ooding, SDS solution ?ooding, or SDS foam ?ooding alone. As the foam stability was enhanced, gas mobility and channelling were controlled effectively. Moreover, sand pack ?ooding results showed that the increase of differential pressure and pro?le control effect were a proportional function of the SiO2 concentration in SiO2/SDS foam. They concluded that higher oil recoveries were obtained when the SiO2 concentration was less than 1.5 wt % and recommended this synergy for oil recovery applications.

4.6. Enhancing oil recovery with nanostablized Pickering emulsions
Emulsion stabilized by solid particles that adsorb at the interface between two phases are referred to as Pickering emulsion ADDIN EN.CITE ;EndNote;;Cite;;Author;J.pickering;/Author;;Year;2001;/Year;;RecNum;137;/RecNum;;DisplayText;123;/DisplayText;;record;;rec-number;137;/rec-number;;foreign-keys;;key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″;137;/key;;key app=”ENWeb” db-id=””;0;/key;;/foreign-keys;;ref-type name=”Journal Article”;17;/ref-type;;contributors;;authors;;author;J.pickering;/author;;/authors;;/contributors;;titles;;title;Pickering emulsions;/title;;secondary-title;Journal of chemical society;/secondary-title;;/titles;;periodical;;full-title;Journal of chemical society;/full-title;;/periodical;;dates;;year;2001;/year;;/dates;;urls;;/urls;;/record;;/Cite;;/EndNote;123. A mixture of oil and water forms small oil droplets which are dispersed throughout the water, eventually, these droplets will coalesce to decrease the amount of energy in the system. However, if solid particles are added to the mixture, they will bind to the surface of the interface and prevent the droplets from coalescing thus, forming a more stable emulsion. The stability of these emulsions, however, depends on the properties of the particles, including its hydrophobicity, shape, and size. The particle’s contact angle to the surface of the droplet is a characteristic of the hydrophobicity. If the contact angle of the particle to the interface is low, the particle will be mostly wetted by the droplet and therefore will not likely prevent coalescence of the droplets.

Currently, surfactants and colloidal solids are used to stabilize emulsions. However, surfactants are expensive and at high reservoir temperatures and in high saline conditions, they are unstable which limits their application as emulsion stabilizers. Temperature, composition, and droplet size are among the major properties of an emulsion, that determine their stability and rheological behaviours ADDIN EN.CITE <EndNote><Cite><Author>Hasan</Author><Year>2010</Year><RecNum>144</RecNum><DisplayText>102</DisplayText><record><rec-number>144</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>144</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hasan, Shadi W</author><author>Ghannam, Mamdouh T</author><author>Esmail, Nabil</author></authors></contributors><titles><title>Heavy crude oil viscosity reduction and rheology for pipeline transportation</title><secondary-title>Fuel</secondary-title></titles><periodical><full-title>Fuel</full-title></periodical><pages>1095-1100</pages><volume>89</volume><number>5</number><dates><year>2010</year></dates><isbn>0016-2361</isbn><urls></urls></record></Cite></EndNote>102. In recent years, nanoparticle-stabilized emulsions have been shown to offer a better emulsion stability. This is because of their specific characteristics and advantages over conventional emulsions stabilized by surfactants or by colloidal particles. The solid nanoparticles can be irreversibly attached to the oil-water interface and form a rigid nanoparticle monolayer on the droplet surfaces, which results in highly stable emulsions that can withstand harsh conditions. In addition, in comparison to colloidal particles, nanoparticles are one hundred times smaller, and emulsions stabilized by them can travel a long distance in reservoirs without much retention. These characteristics contribute to the applicability of these micron-sized particles for EOR applications ADDIN EN.CITE <EndNote><Cite><Author>Kong</Author><Year>2010</Year><RecNum>91</RecNum><DisplayText>9, 30</DisplayText><record><rec-number>91</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525933841″>91</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Kong, Xiangling</author><author>Ohadi, Michael</author></authors></contributors><titles><title>Applications of micro and nano technologies in the oil and gas industry-overview of the recent progress</title><secondary-title>Abu Dhabi international petroleum exhibition and conference</secondary-title></titles><dates><year>2010</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1555633153</isbn><urls></urls></record></Cite><Cite><Author>Zhang</Author><Year>2010</Year><RecNum>116</RecNum><record><rec-number>116</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>116</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Zhang, Tiantian</author><author>Davidson, Drew</author><author>Bryant, Steven Lawrence</author><author>Huh, Chun</author></authors></contributors><titles><title>Nanoparticle-stabilized emulsions for applications in enhanced oil recovery</title><secondary-title>SPE improved oil recovery symposium</secondary-title></titles><dates><year>2010</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1555632890</isbn><urls></urls></record></Cite></EndNote>9, 30.

Several studies have been reported on how nano-stabilized emulsion improve oil recovery, Ki youl et al ADDIN EN.CITE <EndNote><Cite><Author>Yoon</Author><Year>2016</Year><RecNum>96</RecNum><DisplayText>124</DisplayText><record><rec-number>96</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525935565″>96</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Yoon, Ki Youl</author><author>Son, Han Am</author><author>Choi, Sang Koo</author><author>Kim, Jin Woong</author><author>Sung, Won Mo</author><author>Kim, Hyun Tae</author></authors></contributors><titles><title>Core flooding of complex nanoscale colloidal dispersions for enhanced oil recovery by in situ formation of stable oil-in-water pickering emulsions</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2628-2635</pages><volume>30</volume><number>4</number><dates><year>2016</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>124, carried out a core flooding test on a Berea sandstone by flooding a complex silica colloidal dispersion of oil in water, forming a stabilized Pickering emulsion which produced a 4% incremental oil recovery after water flooding. Their colloidal layer consisted of a nanoparticle, surfactant, and a polymer, they used silica nanoparticles, dodecyltimethylammonium bromide (DTAB) as the cationic surfactant, and poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSS-co-MA) as the anionic polymer. The colloidal layer was generated by adsorption of PSS-co-MA on the silica nanoparticle by the effect of van der waals forces of attraction and then adsorbed the DTAB onto the PSS-co-MA layer by electrostatic attraction, which provided a mechanically stable interface. They concluded that emulsions produced in the core could flow readily in the rock pores due to the oil-water interface that made a complex with a colloidal phase that improved the structural stability of the emulsion droplets resulting in incremental oil recovery ADDIN EN.CITE <EndNote><Cite><Author>Yoon</Author><Year>2016</Year><RecNum>96</RecNum><DisplayText>124</DisplayText><record><rec-number>96</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525935565″>96</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Yoon, Ki Youl</author><author>Son, Han Am</author><author>Choi, Sang Koo</author><author>Kim, Jin Woong</author><author>Sung, Won Mo</author><author>Kim, Hyun Tae</author></authors></contributors><titles><title>Core flooding of complex nanoscale colloidal dispersions for enhanced oil recovery by in situ formation of stable oil-in-water pickering emulsions</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2628-2635</pages><volume>30</volume><number>4</number><dates><year>2016</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>124.

4.7. Nanoparticles for inhibition asphaltene and wax deposition
During oil production processes, it is well known that the reservoir conditions such as fluid composition, pressure and temperature keep on changing. These changes may result in precipitation of heavy organic solids such as asphaltenes ADDIN EN.CITE <EndNote><Cite><Author>Montoya</Author><Year>2014</Year><RecNum>103</RecNum><DisplayText>125</DisplayText><record><rec-number>103</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>103</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Montoya, Tatiana</author><author>Coral, Diana</author><author>Franco, Camilo A</author><author>Nassar, Nashaat N</author><author>Corte?s, Farid B</author></authors></contributors><titles><title>A novel solid–liquid equilibrium model for describing the adsorption of associating asphaltene molecules onto solid surfaces based on the “Chemical Theory”</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>4963-4975</pages><volume>28</volume><number>8</number><dates><year>2014</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>125. Asphaltene is one of the most polarizable components with the highest molecular weight and complex structure. Investigations have shown that asphaltenes are dispersed in crude oil by resins as peptizing agents PEVuZE5vdGU+PENpdGU+PEF1dGhvcj5Sb2dlbDwvQXV0aG9yPjxZZWFyPjIwMTA8L1llYXI+PFJl
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ADDIN EN.CITE.DATA 126-128. Asphaltenes consist of aromatic rings attached to hydrocarbon chains and heteroatoms such as oxygen, sulphur, and nitrogen as well as traces of heavy metals like nickel, vanadium and iron, and its complex characterization differs from one crude to another ADDIN EN.CITE <EndNote><Cite><Author>Doryani</Author><Year>2016</Year><RecNum>70</RecNum><DisplayText>129</DisplayText><record><rec-number>70</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>70</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Doryani, H.</author><author>Malayeri, M. R.</author><author>Riazi, M.</author></authors></contributors><titles><title>Visualization of asphaltene precipitation and deposition in a uniformly patterned glass micromodel</title><secondary-title>Fuel</secondary-title></titles><periodical><full-title>Fuel</full-title></periodical><pages>613-622</pages><volume>182</volume><dates><year>2016</year></dates><isbn>00162361</isbn><urls></urls><electronic-resource-num>10.1016/j.fuel.2016.06.004</electronic-resource-num></record></Cite></EndNote>129.
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ADDIN EN.CITE.DATA 130-132. Furthermore, due to their amphiphilic behaviour, asphaltene acts as a surface-active agent and creates oil-water separation difficulties by creating water in oil emulsions. As a result, asphaltenes is undesirable for all crude oil processes because it makes upgrading challenging, costly and environmentally unfriendly ADDIN EN.CITE <EndNote><Cite><Author>Yang</Author><Year>2007</Year><RecNum>119</RecNum><DisplayText>133</DisplayText><record><rec-number>119</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>119</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Yang, Xiaoli</author><author>Verruto, Vincent J</author><author>Kilpatrick, Peter K</author></authors></contributors><titles><title>Dynamic asphaltene? resin exchange at the oil/water interface: Time-dependent W/O emulsion stability for asphaltene/resin model oils</title><secondary-title>Energy &amp; fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1343-1349</pages><volume>21</volume><number>3</number><dates><year>2007</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>133.

Presently, the common prevention measures typically used in removing the deposited asphaltenes in the oil and gas industry include solvent injection, the addition of surfactants, wireline cuttings and many other mechanical treatments. However, these methods are not only costly but also temporary, since asphaltenes can easily redeposit again. In addition, these applied methods used to inhibit asphaltenes at the reservoir level appear to be ineffective; because the asphaltene inhibitors and the dispersants used almost have the similar chemical composition, making it hard to prevent the formation of the residual ADDIN EN.CITE <EndNote><Cite><Author>Zabala</Author><Year>2014</Year><RecNum>262</RecNum><DisplayText>59</DisplayText><record><rec-number>262</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>262</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Zabala, R</author><author>Mora, E</author><author>Botero, OF</author><author>Cespedes, C</author><author>Guarin, L</author><author>Franco, CA</author><author>Cortes, FB</author><author>Patino, JE</author><author>Ospina, N</author></authors></contributors><titles><title>Nano-technology for asphaltenes inhibition in Cupiagua South Wells</title><secondary-title>IPTC 2014: International Petroleum Technology Conference</secondary-title></titles><dates><year>2014</year></dates><isbn>2214-4609</isbn><urls></urls></record></Cite></EndNote>59. As a result, scientists are motivated to search for smart materials and techniques that are more sustainable, efficient and effective and research into nanomaterial application in asphaltene prevention in oil and gas has emerged PEVuZE5vdGU+PENpdGU+PEF1dGhvcj5LYXplbXphZGVoPC9BdXRob3I+PFllYXI+MjAxNTwvWWVh
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ADDIN EN.CITE.DATA 69, 134-136. Researchers have gained interest in using nanoparticles to inhibit asphaltene because of their unique properties, such as their exponentially high surface area to volume ratio which is crucial for adsorption capability ADDIN EN.CITE <EndNote><Cite><Author>Franco</Author><Year>2013</Year><RecNum>261</RecNum><DisplayText>136</DisplayText><record><rec-number>261</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>261</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Franco, Camilo A</author><author>Nassar, Nashaat N</author><author>Ruiz, Marco A</author><author>Pereira-Almao, Pedro</author><author>Corte?s, Farid B</author></authors></contributors><titles><title>Nanoparticles for inhibition of asphaltenes damage: adsorption study and displacement test on porous media</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2899-2907</pages><volume>27</volume><number>6</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>136.
Application of nanotechnology in asphaltene inhibition has been reported in several studies that have been conducted at the laboratory, pilot and field scale. Recently, Nasser et al. conducted a batch study to investigate the potential adsorption effect of asphaltenes using different metal oxides nanoparticles; including FeO4, Co3O4, TiO2, MgO, CaO, and NiO. The asphaltene adsorption capabilities followed the order CaO > Co3O4> FeO4> MgO, NiO> TiO2, the authors concluded that adsorption mainly depends on the metal oxide type ADDIN EN.CITE <EndNote><Cite><Author>Nassar</Author><Year>2011</Year><RecNum>106</RecNum><DisplayText>137</DisplayText><record><rec-number>106</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>106</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nassar, Nashaat N.</author><author>Hassan, Azfar</author><author>Pereira-Almao, Pedro</author></authors></contributors><titles><title>Metal Oxide Nanoparticles for Asphaltene Adsorption and Oxidation</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1017-1023</pages><volume>25</volume><number>3</number><dates><year>2011</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef101230g</electronic-resource-num></record></Cite></EndNote>137. A similar study by Mohammad et al. ADDIN EN.CITE <EndNote><Cite><Author>Mohammadi</Author><Year>2011</Year><RecNum>260</RecNum><DisplayText>135</DisplayText><record><rec-number>260</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>260</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Mohammadi, Mohsen</author><author>Akbari, Mahdi</author><author>Fakhroueian, Zahra</author><author>Bahramian, Alireza</author><author>Azin, Reza</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Inhibition of asphaltene precipitation by TiO2, SiO2, and ZrO2 nanofluids</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3150-3156</pages><volume>25</volume><number>7</number><dates><year>2011</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>135 investigated how TiO2, ZrO2 and, SiO2 nanoparticles can improve the stability of asphaltene. They concluded that because of the formation of hydrogen bonds in acidic conditions, TiO2 nanofluids can enhance the asphaltene stability. The reverse was true for the basic conditions because of the absence of hydrogen bonds. They concluded that the surface acidity of the adsorbent can enhance asphaltene stability ADDIN EN.CITE <EndNote><Cite><Author>Mohammadi</Author><Year>2011</Year><RecNum>107</RecNum><DisplayText>138</DisplayText><record><rec-number>107</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>107</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Mohammadi, Mohsen</author><author>Akbari, Mahdi</author><author>Fakhroueian, Zahra</author><author>Bahramian, Alireza</author><author>Azin, Reza</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Inhibition of Asphaltene Precipitation by TiO2, SiO2, and ZrO2Nanofluids</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3150-3156</pages><volume>25</volume><number>7</number><dates><year>2011</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef2001635</electronic-resource-num></record></Cite></EndNote>138. These findings are in agreement with Nassar et al. ADDIN EN.CITE <EndNote><Cite><Author>Nassar</Author><Year>2011</Year><RecNum>110</RecNum><DisplayText>139</DisplayText><record><rec-number>110</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>110</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nassar, Nashaat N</author><author>Hassan, Azfar</author><author>Pereira-Almao, Pedro</author></authors></contributors><titles><title>Effect of surface acidity and basicity of aluminas on asphaltene adsorption and oxidation</title><secondary-title>Journal of colloid and interface science</secondary-title></titles><periodical><full-title>Journal of colloid and interface science</full-title></periodical><pages>233-238</pages><volume>360</volume><number>1</number><dates><year>2011</year></dates><isbn>0021-9797</isbn><urls></urls></record></Cite></EndNote>139 who studied the effect of surface acidity and basicity of the alumina nanoparticles on asphaltene adsorption, concluding the adsorption capability of asphaltenes on to the alumina nanoparticles followed the order, acidic > basic > neutral. This signifies that using specific acids as functionalizing agents can significantly improve the adsorbent-adsorbate interactions.

Yousef et al ADDIN EN.CITE <EndNote><Cite><Author>Kazemzadeh</Author><Year>2015</Year><RecNum>121</RecNum><DisplayText>69</DisplayText><record><rec-number>121</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>121</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Kazemzadeh, Yousef</author><author>Eshraghi, S Ehsan</author><author>Kazemi, Keyvan</author><author>Sourani, Saeed</author><author>Mehrabi, Mehran</author><author>Ahmadi, Yaser</author></authors></contributors><titles><title>Behavior of asphaltene adsorption onto the metal oxide nanoparticle surface and its effect on heavy oil recovery</title><secondary-title>Industrial &amp; Engineering Chemistry Research</secondary-title></titles><periodical><full-title>Industrial &amp; Engineering Chemistry Research</full-title></periodical><pages>233-239</pages><volume>54</volume><number>1</number><dates><year>2015</year></dates><isbn>0888-5885</isbn><urls></urls></record></Cite></EndNote>69 also investigated the behaviour of asphaltene adsorption on other metal oxide types. SiO2, NiO and Fe3O4 nanoparticles were tested in a micro glass module to determine how they absorb asphaltene and prevent its precipitation. The authors concluded that increasing n-heptane in the presence of the nanoparticles resulted in more adsorption regardless of the type of nanomaterial used. This enhanced the perdurability of asphaltene precipitation, however for selection purposes, they noted that the adsorption of asphaltenes followed the order SiO2>NiO >Fe3O4 which implies that silicate nanoparticles have more affinity to asphaltene than NiO or Fe3O4.

Camilo et al. ADDIN EN.CITE <EndNote><Cite><Author>Franco</Author><Year>2013</Year><RecNum>261</RecNum><DisplayText>136</DisplayText><record><rec-number>261</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>261</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Franco, Camilo A</author><author>Nassar, Nashaat N</author><author>Ruiz, Marco A</author><author>Pereira-Almao, Pedro</author><author>Corte?s, Farid B</author></authors></contributors><titles><title>Nanoparticles for inhibition of asphaltenes damage: adsorption study and displacement test on porous media</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2899-2907</pages><volume>27</volume><number>6</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>136 investigated the effect of the chemical nature of 12 types of nanoparticles on asphaltene adsorption on a porous medium under flow conditions at reservoir temperature and pressure. They reported fast adsorption of asphaltenes on the nanoparticles surface, indicating the promising nature of adsorbents for delaying the agglomeration and inhibiting the precipitation and deposition of asphaltenes. The authors concluded that due to the ability of the adsorbents to absorb and stabilize the asphaltene content, the nanoparticles were able to restore production which led to improvement in oil recovery ADDIN EN.CITE <EndNote><Cite><Author>Franco</Author><Year>2013</Year><RecNum>261</RecNum><DisplayText>136</DisplayText><record><rec-number>261</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>261</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Franco, Camilo A</author><author>Nassar, Nashaat N</author><author>Ruiz, Marco A</author><author>Pereira-Almao, Pedro</author><author>Corte?s, Farid B</author></authors></contributors><titles><title>Nanoparticles for inhibition of asphaltenes damage: adsorption study and displacement test on porous media</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2899-2907</pages><volume>27</volume><number>6</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>136. Nanoparticles are clearly a promising technique for asphaltene deposition control during oil and gas recovery.

A successful field test was conducted by Zabala and coworkers ADDIN EN.CITE <EndNote><Cite><Author>Zabala</Author><Year>2014</Year><RecNum>262</RecNum><DisplayText>59</DisplayText><record><rec-number>262</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>262</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Zabala, R</author><author>Mora, E</author><author>Botero, OF</author><author>Cespedes, C</author><author>Guarin, L</author><author>Franco, CA</author><author>Cortes, FB</author><author>Patino, JE</author><author>Ospina, N</author></authors></contributors><titles><title>Nano-technology for asphaltenes inhibition in Cupiagua South Wells</title><secondary-title>IPTC 2014: International Petroleum Technology Conference</secondary-title></titles><dates><year>2014</year></dates><isbn>2214-4609</isbn><urls></urls></record></Cite></EndNote>59, who applied commercial aluminium-based nanofluids to prevent formation damage that was caused by asphaltenes. They first conducted a core flood test and later performed a field test by injecting aluminium based nanofluids for asphaltene inhibition in the Cupiagua sur oil field in Colombia. They reported a cumulative oil production of 150,000 barrels of oil after 271 days with use of alumina nanoparticle injection. The authors concluded that well-stabilized alumina-based nanofluids have good retention in the formation for longer than 8 months, they suggested that these nanoparticles may be applicable to the reservoir with very low permeability conditions ADDIN EN.CITE <EndNote><Cite><Author>Zabala</Author><Year>2014</Year><RecNum>262</RecNum><DisplayText>59</DisplayText><record><rec-number>262</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>262</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Zabala, R</author><author>Mora, E</author><author>Botero, OF</author><author>Cespedes, C</author><author>Guarin, L</author><author>Franco, CA</author><author>Cortes, FB</author><author>Patino, JE</author><author>Ospina, N</author></authors></contributors><titles><title>Nano-technology for asphaltenes inhibition in Cupiagua South Wells</title><secondary-title>IPTC 2014: International Petroleum Technology Conference</secondary-title></titles><dates><year>2014</year></dates><isbn>2214-4609</isbn><urls></urls></record></Cite></EndNote>59.

Nanoparticle application for wax inhibition has also become an attractive study among different researchers recently. Norman et al. ADDIN EN.CITE <EndNote><Cite><Author>Norrman</Author><Year>2016</Year><RecNum>32</RecNum><DisplayText>140</DisplayText><record><rec-number>32</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>32</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Norrman, Jens</author><author>Solberg, Amalie</author><author>Sjoblom, Johan</author><author>Paso, Kristofer</author></authors></contributors><titles><title>Nanoparticles for waxy crudes: Effect of polymer coverage and the effect on wax crystallization</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>5108-5114</pages><volume>30</volume><number>6</number><dates><year>2016</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>140 investigated the effect of the amount of coating materials by coating the nanoparticles with poly (octadecyl acrylate) (POA) on pour-point depressants and compared them with bare nanoparticles. They used a waxy model oil system to demonstrate the pour-point depressing performance. Their study focused on how the amount of coverage of the nanoparticles could a?ect their performance. The adsorption of the poly (octadecyl acrylate) (POA) on silica was determined using a quartz crystal microbalance with dissipation monitoring (QCM-D). The nanoparticle performance was estimated with rheology tests to determine the di?erences in the strength of the wax gel formed, with di?erential scanning calorimetry (DSC) to assess the wax appearance temperature and any di?erences in crystallization, and visual observation of the formed wax with polarized microscopy. Rheological measurements showed that nanoparticles with low POA coverage had almost no e?ect on the strength of the formed wax gel, while nanoparticles with full coverage of POA signi?cantly lowered the wax gel strength. Results from the DSC also showed that the wax appearance temperature is lowered by the nanoparticles and that there is little or no e?ect when using nanoparticles with more POA than 100% coverage. DSC also showed that the presence of the nanoparticles changes the nature of the wax crystallization, most likely by introducing multiple nucleation centres, causing a sharp peak in crystallization. Polarized microscopy showed that, in the presence of the nanoparticles, large particles were formed, compared to those with the added silica. The research conducted showed that it is possible to optimize the e?ect of coated nanoparticles on wax gels, so that already low dosages provided by such particles may be further reduced, improving economic and environmental viability ADDIN EN.CITE <EndNote><Cite><Author>Norrman</Author><Year>2016</Year><RecNum>32</RecNum><DisplayText>140</DisplayText><record><rec-number>32</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>32</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Norrman, Jens</author><author>Solberg, Amalie</author><author>Sjoblom, Johan</author><author>Paso, Kristofer</author></authors></contributors><titles><title>Nanoparticles for waxy crudes: Effect of polymer coverage and the effect on wax crystallization</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>5108-5114</pages><volume>30</volume><number>6</number><dates><year>2016</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>140.

4.8. Enhanced oil recovery due to structural disjoining pressure caused by nanoparticles
It has been found that structural disjoining pressure is one of the crucial factors that influence the fluid spreading dynamics on the surface ADDIN EN.CITE <EndNote><Cite><Author>Wasan</Author><Year>2003</Year><RecNum>178</RecNum><DisplayText>86, 117</DisplayText><record><rec-number>178</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>178</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wasan, Darsh T</author><author>Nikolov, Alex D</author></authors></contributors><titles><title>Spreading of nanofluids on solids</title><secondary-title>Nature</secondary-title></titles><periodical><full-title>Nature</full-title></periodical><pages>156</pages><volume>423</volume><number>6936</number><dates><year>2003</year></dates><isbn>0028-0836</isbn><urls></urls></record></Cite><Cite><Author>Kondiparty</Author><Year>2011</Year><RecNum>179</RecNum><record><rec-number>179</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>179</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Kondiparty, Kirti</author><author>Nikolov, Alex</author><author>Wu, Stanley</author><author>Wasan, Darsh</author></authors></contributors><titles><title>Wetting and spreading of nanofluids on solid surfaces driven by the structural disjoining pressure: statics analysis and experiments</title><secondary-title>Langmuir</secondary-title></titles><periodical><full-title>Langmuir</full-title></periodical><pages>3324-3335</pages><volume>27</volume><number>7</number><dates><year>2011</year></dates><isbn>0743-7463</isbn><urls></urls></record></Cite></EndNote>86, 117. Studies have shown that the presence of nanoparticles in three contact phases and contact regions tend to create a wedge-film structure that forms this driving force ADDIN EN.CITE <EndNote><Cite><Author>Wasan</Author><Year>2011</Year><RecNum>59</RecNum><DisplayText>37</DisplayText><record><rec-number>59</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>59</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wasan, Darsh</author><author>Nikolov, Alex</author><author>Kondiparty, Kirti</author></authors></contributors><titles><title>The wetting and spreading of nanofluids on solids: Role of the structural disjoining pressure</title><secondary-title>Current Opinion in Colloid &amp; Interface Science</secondary-title></titles><periodical><full-title>Current Opinion in Colloid &amp; Interface Science</full-title></periodical><pages>344-349</pages><volume>16</volume><number>4</number><dates><year>2011</year></dates><isbn>1359-0294</isbn><urls></urls></record></Cite></EndNote>37 as shown schematically in Figure 4.

Figure 4. Illustration of the nature of the forces operating at the three-phase contact line in the presence of nanoparticles
Structural disjoining pressure is correlated with the ability of the fluid to spread on the surface as a result of the interfacial tension imbalance between the solid, oil phase and an aqueous phase ADDIN EN.CITE <EndNote><Cite><Author>Wasan</Author><Year>2011</Year><RecNum>59</RecNum><DisplayText>37</DisplayText><record><rec-number>59</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>59</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wasan, Darsh</author><author>Nikolov, Alex</author><author>Kondiparty, Kirti</author></authors></contributors><titles><title>The wetting and spreading of nanofluids on solids: Role of the structural disjoining pressure</title><secondary-title>Current Opinion in Colloid &amp; Interface Science</secondary-title></titles><periodical><full-title>Current Opinion in Colloid &amp; Interface Science</full-title></periodical><pages>344-349</pages><volume>16</volume><number>4</number><dates><year>2011</year></dates><isbn>1359-0294</isbn><urls></urls></record></Cite></EndNote>37. These interfacial forces decrease the contact angle of the aqueous phase (nanofluids) to almost 1o resulting into a wedge film. This wedge film acts to separate formation fluids such as oil from the formation surface ADDIN EN.CITE <EndNote><Cite><Author>Chengara</Author><Year>2004</Year><RecNum>181</RecNum><DisplayText>118</DisplayText><record><rec-number>181</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>181</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Chengara, Anoop</author><author>Nikolov, Alex D</author><author>Wasan, Darsh T</author><author>Trokhymchuk, Andrij</author><author>Henderson, Douglas</author></authors></contributors><titles><title>Spreading of nanofluids driven by the structural disjoining pressure gradient</title><secondary-title>Journal of colloid and interface science</secondary-title></titles><periodical><full-title>Journal of colloid and interface science</full-title></periodical><pages>192-201</pages><volume>280</volume><number>1</number><dates><year>2004</year></dates><isbn>0021-9797</isbn><urls></urls></record></Cite></EndNote>118. The spreading coefficient of the fluid increases exponentially as the film thickness decreases ADDIN EN.CITE <EndNote><Cite><Author>Chengara</Author><Year>2004</Year><RecNum>181</RecNum><DisplayText>118, 141</DisplayText><record><rec-number>181</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>181</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Chengara, Anoop</author><author>Nikolov, Alex D</author><author>Wasan, Darsh T</author><author>Trokhymchuk, Andrij</author><author>Henderson, Douglas</author></authors></contributors><titles><title>Spreading of nanofluids driven by the structural disjoining pressure gradient</title><secondary-title>Journal of colloid and interface science</secondary-title></titles><periodical><full-title>Journal of colloid and interface science</full-title></periodical><pages>192-201</pages><volume>280</volume><number>1</number><dates><year>2004</year></dates><isbn>0021-9797</isbn><urls></urls></record></Cite><Cite><Author>Dai</Author><Year>2017</Year><RecNum>88</RecNum><record><rec-number>88</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>88</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Dai, Caili</author><author>Wang, Xinke</author><author>Li, Yuyang</author><author>Lv, Wenjiao</author><author>Zou, Chenwei</author><author>Gao, Mingwei</author><author>Zhao, Mingwei</author></authors></contributors><titles><title>Spontaneous imbibition investigation of self-dispersing silica nanofluids for enhanced oil recovery in low-permeability cores</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2663-2668</pages><volume>31</volume><number>3</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>118, 141, and the driving force for the spreading of the nanofluids is the structural disjoining pressure gradient or film tension gradient (??) which is directed towards the wedge from the bulk solution. This gradient is higher at the vertex because of the nanoparticle structuring in the wedge confinement as shown in Figure 5. It drives the nanoparticles to spread at the wedge tips as the gradient increases towards the vertex of the wedge. ADDIN EN.CITE <EndNote><Cite><Author>Wasan</Author><Year>2011</Year><RecNum>59</RecNum><DisplayText>37</DisplayText><record><rec-number>59</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>59</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wasan, Darsh</author><author>Nikolov, Alex</author><author>Kondiparty, Kirti</author></authors></contributors><titles><title>The wetting and spreading of nanofluids on solids: Role of the structural disjoining pressure</title><secondary-title>Current Opinion in Colloid &amp; Interface Science</secondary-title></titles><periodical><full-title>Current Opinion in Colloid &amp; Interface Science</full-title></periodical><pages>344-349</pages><volume>16</volume><number>4</number><dates><year>2011</year></dates><isbn>1359-0294</isbn><urls></urls></record></Cite></EndNote>37. Hua et al ADDIN EN.CITE <EndNote><Cite><Author>Recovery</Author><Year>2014</Year><RecNum>201</RecNum><DisplayText>142</DisplayText><record><rec-number>201</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>201</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Recovery, Enhanced Oil</author></authors></contributors><titles><title>Using Nanoparticle Dispersions: Underlying Mechanism and Imbibition Experiments Zhang, Hua; Nikolov, Alex; Wasan, Darsh</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3002-3009</pages><volume>28</volume><number>5</number><dates><year>2014</year></dates><urls></urls></record></Cite></EndNote>142, suggests that in order to optimize the recovery with nanofluids using the structural disjoining pressure, the formulation need to contain small nanoparticles with low polydispersity. According to their observation, higher variations of particle sizes or higher polydispersity tends to reduce the structural disjoining pressure. They also realized that as a rule of thumb, the formulated nanofluids should have a higher osmotic pressure of at least approximately 200 Pa for 10 Vol % nanofluids. An analytical expression using the Laplace transformation was developed by Trokhymchuk et al. ADDIN EN.CITE <EndNote><Cite><Author>Trokhymchuk</Author><Year>2001</Year><RecNum>202</RecNum><DisplayText>143</DisplayText><record><rec-number>202</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>202</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Trokhymchuk, Andrij</author><author>Henderson, Douglas</author><author>Nikolov, Alex</author><author>Wasan, Darsh T</author></authors></contributors><titles><title>A simple calculation of structural and depletion forces for fluids/suspensions confined in a film</title><secondary-title>Langmuir</secondary-title></titles><periodical><full-title>Langmuir</full-title></periodical><pages>4940-4947</pages><volume>17</volume><number>16</number><dates><year>2001</year></dates><isbn>0743-7463</isbn><urls></urls></record></Cite></EndNote>143 for estimating the structural disjoining pressure for any solution with nanofluids. This simple analytical expression can be applied to understand the stability of liquid films containing colloidal particles. This expression was given as,
?st(h)=-p 0<h<d?ocos(?h+?2)e-kh+?1e-?(h-d), h>d (2)Where d is the diameter of the nanoparticle, h is the wedge film thickness, and the other parameters (?o, ?1, ?, ?2, k, ?) are fitted as cubic polynomials in terms of the nanofluid volume fraction (?) and P is the osmotic pressure which is a function of the nanofluids volume fraction given by the equation below,
?kT(1+?+?2 -?3((1-?)3) (3)
Where ? is the particle number density, k is the Boltzmann constant and T is the temperature. From the equation above, the structural disjoining pressure and osmotic pressure increases as the volume of the nanofluids fraction increases. Also, a small three phase contact angle between the nanofluids/oil and rock is desired to maximize the structure disjoining pressure.

Figure 5. Nanoparticle structuring in the wedge-?lm resulting in structural disjoining pressure gradient at the wedge vertex ADDIN EN.CITE <EndNote><Cite><Author>Wasan</Author><Year>2011</Year><RecNum>59</RecNum><DisplayText>37</DisplayText><record><rec-number>59</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>59</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wasan, Darsh</author><author>Nikolov, Alex</author><author>Kondiparty, Kirti</author></authors></contributors><titles><title>The wetting and spreading of nanofluids on solids: Role of the structural disjoining pressure</title><secondary-title>Current Opinion in Colloid &amp; Interface Science</secondary-title></titles><periodical><full-title>Current Opinion in Colloid &amp; Interface Science</full-title></periodical><pages>344-349</pages><volume>16</volume><number>4</number><dates><year>2011</year></dates><isbn>1359-0294</isbn><urls></urls></record></Cite></EndNote>37.5. Effect of various factors on nanoparticle performanceMany different studies have tested the effects of various parameters on oil recovery during nanofluids flooding. A summary of most of these factors that influence nanoparticle enhanced recovery is discussed in the following sections.

5.1. Salinity
The stability of nanofluids in different saline environments is one of the critical issues that must be considered during flooding, especially for the subsurface applications. Nanofluids are greatly affected and almost fail in the presence of oppositely charged ions due to excessive charge screening ADDIN EN.CITE <EndNote><Cite><Author>Ranka</Author><Year>2015</Year><RecNum>21</RecNum><DisplayText>144</DisplayText><record><rec-number>21</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>21</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Ranka, Mikhil</author><author>Brown, Paul</author><author>Hatton, T Alan</author></authors></contributors><titles><title>Responsive stabilization of nanoparticles for extreme salinity and high-temperature reservoir applications</title><secondary-title>ACS applied materials &amp; interfaces</secondary-title></titles><periodical><full-title>ACS applied materials &amp; interfaces</full-title></periodical><pages>19651-19658</pages><volume>7</volume><number>35</number><dates><year>2015</year></dates><isbn>1944-8244</isbn><urls></urls></record></Cite></EndNote>144. The retention of nanoparticles in brine solution may be due to the electrostatic attraction between the negatively charged particle cluster and parts of the formation surface with a positive zeta potential ADDIN EN.CITE <EndNote><Cite><Author>Nazari Moghaddam</Author><Year>2015</Year><RecNum>52</RecNum><DisplayText>55</DisplayText><record><rec-number>52</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>52</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nazari Moghaddam, Rasoul</author><author>Bahramian, Alireza</author><author>Fakhroueian, Zahra</author><author>Karimi, Ali</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Comparative Study of Using Nanoparticles for Enhanced Oil Recovery: Wettability Alteration of Carbonate Rocks</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2111-2119</pages><volume>29</volume><number>4</number><dates><year>2015</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef5024719</electronic-resource-num></record></Cite></EndNote>55. Several researchers have concluded that the most non-interacting nanoparticles can be small particles with zero charge ADDIN EN.CITE <EndNote><Cite><Author>Nazari Moghaddam</Author><Year>2015</Year><RecNum>52</RecNum><DisplayText>55, 145</DisplayText><record><rec-number>52</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>52</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nazari Moghaddam, Rasoul</author><author>Bahramian, Alireza</author><author>Fakhroueian, Zahra</author><author>Karimi, Ali</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Comparative Study of Using Nanoparticles for Enhanced Oil Recovery: Wettability Alteration of Carbonate Rocks</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2111-2119</pages><volume>29</volume><number>4</number><dates><year>2015</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef5024719</electronic-resource-num></record></Cite><Cite><Author>Li</Author><Year>2014</Year><RecNum>194</RecNum><record><rec-number>194</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>194</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Li, Yan Vivian</author><author>Cathles, Lawrence M</author><author>Archer, Lynden A</author></authors></contributors><titles><title>Nanoparticle tracers in calcium carbonate porous media</title><secondary-title>Journal of nanoparticle research</secondary-title></titles><periodical><full-title>Journal of Nanoparticle Research</full-title></periodical><pages>2541</pages><volume>16</volume><number>8</number><dates><year>2014</year></dates><isbn>1388-0764</isbn><urls></urls></record></Cite></EndNote>55, 145. Polyelectrolytes are always encapsulated on the surfaces of nanoparticles but always fail in high salinity conditions. However, special polymers have been proposed to work in high saline conditions. Mikhil et al ADDIN EN.CITE <EndNote><Cite><Author>Ranka</Author><Year>2015</Year><RecNum>21</RecNum><DisplayText>144</DisplayText><record><rec-number>21</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>21</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Ranka, Mikhil</author><author>Brown, Paul</author><author>Hatton, T Alan</author></authors></contributors><titles><title>Responsive stabilization of nanoparticles for extreme salinity and high-temperature reservoir applications</title><secondary-title>ACS applied materials &amp; interfaces</secondary-title></titles><periodical><full-title>ACS applied materials &amp; interfaces</full-title></periodical><pages>19651-19658</pages><volume>7</volume><number>35</number><dates><year>2015</year></dates><isbn>1944-8244</isbn><urls></urls></record></Cite></EndNote>144 recently reported that nanoparticles stabilized with polyampholyte polymers can be applied to reservoirs with extreme salinity up to 120,000 mg/dm3 and long-term colloidal stability can be achieved.

5.2. Nanoparticle concentration
Nanoparticle concentration is an important factor that effects nanoparticle enhanced oil recovery however, it is not guaranteed that a high particle concentration yields higher oil recovery, and there is always an optimum concentration that should be injected to maximize the oil recovery. In a study carried out by Teng et al ADDIN EN.CITE <EndNote><Cite><Author>Lu</Author><Year>2017</Year><RecNum>195</RecNum><DisplayText>146</DisplayText><record><rec-number>195</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>195</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Lu, Teng</author><author>Li, Zhaomin</author><author>Zhou, Yan</author></authors></contributors><titles><title>Flow Behavior and Displacement Mechanisms of Nanoparticle Stabilized Foam Flooding for Enhanced Heavy Oil Recovery</title><secondary-title>Energies</secondary-title></titles><periodical><full-title>Energies</full-title></periodical><pages>560</pages><volume>10</volume><number>4</number><dates><year>2017</year></dates><urls></urls></record></Cite></EndNote>146 to investigate the effects of the nanoparticle concentration on tertiary oil recovery by nanoparticle-surfactant-stabilized foam flooding, several flooding were carried out with nanoparticle concentrations ranging from 0 to 1.0%. In their study, the concentration of the surfactant was kept constant at 0.5 wt %. For these tests, the injection rates of the nanoparticle-surfactant dispersion and nanoparticle fluids were both set to be 0.5 mL/min. As shown in Figure 6, which shows the oil recovery as a function of the nanoparticle concentration, there was a significant increase in recovery with concentrations between 0.1 wt% and 0.5 wt %. Afterwards, the increase in oil recovery with the nanoparticle concentration became very slight. In that study, 0.5 wt% nanoparticle concentration was the optimum concentration in nanoparticle-stabilized foam flooding. Using nanoparticle concentration beyond the optimum may not only have cost implications but also can result in core plugging that can cause changes in the formation properties. An example is permeability impairment, which can affect the flow of the fluids in the porous media as shown in Figure 7, the impairment increased as the nanoparticle concentration increased ADDIN EN.CITE <EndNote><Cite><Author>Lu</Author><Year>2017</Year><RecNum>99</RecNum><DisplayText>147</DisplayText><record><rec-number>99</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525937543″>99</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Lu, Teng</author><author>Li, Zhaomin</author><author>Zhou, Yan</author><author>Zhang, Chao</author></authors></contributors><titles><title>Enhanced oil recovery of low-permeability cores by SiO2 nanofluid</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>5612-5621</pages><volume>31</volume><number>5</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>147.

18389602125980Nanoparticle concentration
0Nanoparticle concentration

Figure 6. Effect of oil recovery on nanoparticle concentration obtained from reference ADDIN EN.CITE <EndNote><Cite><Author>Lu</Author><Year>2017</Year><RecNum>195</RecNum><DisplayText>146</DisplayText><record><rec-number>195</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>195</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Lu, Teng</author><author>Li, Zhaomin</author><author>Zhou, Yan</author></authors></contributors><titles><title>Flow Behavior and Displacement Mechanisms of Nanoparticle Stabilized Foam Flooding for Enhanced Heavy Oil Recovery</title><secondary-title>Energies</secondary-title></titles><periodical><full-title>Energies</full-title></periodical><pages>560</pages><volume>10</volume><number>4</number><dates><year>2017</year></dates><urls></urls></record></Cite></EndNote>146.

Figure 7. SEM images of the core at different nanoparticle concentrations showing permeability impairment(red circles) caused by injection of nanofluids ADDIN EN.CITE <EndNote><Cite><Author>Lu</Author><Year>2017</Year><RecNum>99</RecNum><DisplayText>147</DisplayText><record><rec-number>99</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525937543″>99</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Lu, Teng</author><author>Li, Zhaomin</author><author>Zhou, Yan</author><author>Zhang, Chao</author></authors></contributors><titles><title>Enhanced oil recovery of low-permeability cores by SiO2 nanofluid</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>5612-5621</pages><volume>31</volume><number>5</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>147.

5.3. Nanoparticle type and size
Nanoparticle types and size also affect oil recovery. Manan et al ADDIN EN.CITE <EndNote><Cite><Author>Manan</Author><Year>2015</Year><RecNum>159</RecNum><DisplayText>148</DisplayText><record><rec-number>159</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>159</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Manan, MA</author><author>Farad, S</author><author>Piroozian, A</author><author>Esmail, MJA</author></authors></contributors><titles><title>Effects of nanoparticle types on carbon dioxide foam flooding in enhanced oil recovery</title><secondary-title>Petroleum Science and Technology</secondary-title></titles><periodical><full-title>Petroleum Science and Technology</full-title></periodical><pages>1286-1294</pages><volume>33</volume><number>12</number><dates><year>2015</year></dates><isbn>1091-6466</isbn><urls></urls></record></Cite></EndNote>148 investigated the effects of nanoparticles of Al2O3, SiO2, TiO2, and CuO. As shown in Figure 8, it was observed that the addition of nanoparticles improved the oil recovery after water ?ooding. An additional 14% of initial oil in place was recovered by injecting a 0.8 PV solution containing nanoparticles of Al2O3, followed by SiO2 which displaced 11% recovery at 1 PV. Both TiO2 and CuO nanoparticles recovered 5% at 0.4PV. However, the selection on the nano-type depends on the intended purpose, some nano-type are good agents in altering wettability, reducing oil viscosity, adsorbing asphaltenes, reducing IFT or other recovery technique, and so a clear understanding of the situation is needed prior to the nanoparticle type selection. For example, the authors carried out a series of screening tests from spontaneous imbibition tests and contact angle measurements to test their ability of different nanofluids to alter the wettability of carbonate rocks. Of nanofluids containing zirconium dioxide (ZrO2), calcium carbonate (CaCO3), titanium dioxide (TiO2), silicon dioxide (SiO2), magnesium oxide (MgO), aluminum oxide (Al2O3), cerium oxide (CeO), and carbon nanotube (CNT), the authors found out that CaCO3 and SiO2 nanoparticles were the best agents for this application ADDIN EN.CITE <EndNote><Cite><Author>Nazari Moghaddam</Author><Year>2015</Year><RecNum>52</RecNum><DisplayText>55</DisplayText><record><rec-number>52</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>52</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nazari Moghaddam, Rasoul</author><author>Bahramian, Alireza</author><author>Fakhroueian, Zahra</author><author>Karimi, Ali</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Comparative Study of Using Nanoparticles for Enhanced Oil Recovery: Wettability Alteration of Carbonate Rocks</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2111-2119</pages><volume>29</volume><number>4</number><dates><year>2015</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef5024719</electronic-resource-num></record></Cite></EndNote>55.

Figure 8. Effects of different nanoparticle types on oil recovery ADDIN EN.CITE <EndNote><Cite><Author>Manan</Author><Year>2015</Year><RecNum>159</RecNum><DisplayText>148</DisplayText><record><rec-number>159</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>159</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Manan, MA</author><author>Farad, S</author><author>Piroozian, A</author><author>Esmail, MJA</author></authors></contributors><titles><title>Effects of nanoparticle types on carbon dioxide foam flooding in enhanced oil recovery</title><secondary-title>Petroleum Science and Technology</secondary-title></titles><periodical><full-title>Petroleum Science and Technology</full-title></periodical><pages>1286-1294</pages><volume>33</volume><number>12</number><dates><year>2015</year></dates><isbn>1091-6466</isbn><urls></urls></record></Cite></EndNote>148.

On the other hand, nanoparticle size influences increment oil recovery as shown in Figure 9. Previously; Luky et al ADDIN EN.CITE <EndNote><Cite><Author>Jain</Author><Year>2009</Year><RecNum>171</RecNum><DisplayText>51</DisplayText><record><rec-number>171</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>171</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Jain, Nirmesh</author><author>Wang, Yanjun</author><author>Jones, Stephen K</author><author>Hawkett, Brian S</author><author>Warr, Gregory G</author></authors></contributors><titles><title>Optimized steric stabilization of aqueous ferrofluids and magnetic nanoparticles</title><secondary-title>Langmuir</secondary-title></titles><periodical><full-title>Langmuir</full-title></periodical><pages>4465-4472</pages><volume>26</volume><number>6</number><dates><year>2009</year></dates><isbn>0743-7463</isbn><urls></urls></record></Cite></EndNote>51 conducted a study to determine the effects of some parameters influencing enhanced oil recovery process using silica nanoparticles using three different sizes of nanoparticles (e.g., 7, 14 and 40 nm) of their single particle sizes. The authors showed that nanoparticles size had an obvious influence on incremental oil recovery. However, the variation of residual oil saturation after waterflooding did not show a direct relationship between particle size and incremental oil recovery. This result can be observed from cores S1 and S2 whereas higher residual oil recovery after waterflooding gave higher incremental oil recovery after Nano-EOR, while the results from cores S3 and S4 showed the opposite effect. However, the trend still showed that increasing nanoparticle size decreased incremental oil recovery at relatively similar residual oil recovery. The highest incremental oil recovery was achieved from the smallest nanoparticle size. The trend shows also incremental oil recovery and displacement efficiency due to Nano-EOR increases as nanoparticle size decreases ADDIN EN.CITE <EndNote><Cite><Author>Jain</Author><Year>2009</Year><RecNum>171</RecNum><DisplayText>51</DisplayText><record><rec-number>171</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>171</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Jain, Nirmesh</author><author>Wang, Yanjun</author><author>Jones, Stephen K</author><author>Hawkett, Brian S</author><author>Warr, Gregory G</author></authors></contributors><titles><title>Optimized steric stabilization of aqueous ferrofluids and magnetic nanoparticles</title><secondary-title>Langmuir</secondary-title></titles><periodical><full-title>Langmuir</full-title></periodical><pages>4465-4472</pages><volume>26</volume><number>6</number><dates><year>2009</year></dates><isbn>0743-7463</isbn><urls></urls></record></Cite></EndNote>51.

Figure 9. Effect of nanoparticle size on oil recovery ADDIN EN.CITE <EndNote><Cite><Author>Jain</Author><Year>2009</Year><RecNum>171</RecNum><DisplayText>51</DisplayText><record><rec-number>171</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>171</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Jain, Nirmesh</author><author>Wang, Yanjun</author><author>Jones, Stephen K</author><author>Hawkett, Brian S</author><author>Warr, Gregory G</author></authors></contributors><titles><title>Optimized steric stabilization of aqueous ferrofluids and magnetic nanoparticles</title><secondary-title>Langmuir</secondary-title></titles><periodical><full-title>Langmuir</full-title></periodical><pages>4465-4472</pages><volume>26</volume><number>6</number><dates><year>2009</year></dates><isbn>0743-7463</isbn><urls></urls></record></Cite></EndNote>51.

5.4. Injection rate
Nanofluids injection rate is also one of the factors that influence the incremental oil recovery of nanofluids flooding. Increasing nanofluids injection rates can significantly decrease incremental oil recovery. Nanoparticles tend to agglomerate as time increases, so increasing the injection rate may affect accumulating nanoparticles near the core inlet rather than flowing through the pore throat ADDIN EN.CITE <EndNote><Cite><Author>Jain</Author><Year>2009</Year><RecNum>171</RecNum><DisplayText>51</DisplayText><record><rec-number>171</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>171</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Jain, Nirmesh</author><author>Wang, Yanjun</author><author>Jones, Stephen K</author><author>Hawkett, Brian S</author><author>Warr, Gregory G</author></authors></contributors><titles><title>Optimized steric stabilization of aqueous ferrofluids and magnetic nanoparticles</title><secondary-title>Langmuir</secondary-title></titles><periodical><full-title>Langmuir</full-title></periodical><pages>4465-4472</pages><volume>26</volume><number>6</number><dates><year>2009</year></dates><isbn>0743-7463</isbn><urls></urls></record></Cite></EndNote>51. An optimized injection rate is therefore always desired to maximize the oil recovery. Also, due to viscous fingering in cases where the oil viscosity is greater than that of the nanofluids, higher injection rates may cause unfavourable mobility ratios that could affect the sweep efficiency which in turn results in lower oil recovery rates ADDIN EN.CITE <EndNote><Cite><Author>Sharma</Author><Year>2014</Year><RecNum>100</RecNum><DisplayText>149, 150</DisplayText><record><rec-number>100</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525937850″>100</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Sharma, Tushar</author><author>Suresh Kumar, G</author><author>Sangwai, Jitendra S</author></authors></contributors><titles><title>Enhanced oil recovery using oil-in-water (o/w) emulsion stabilized by nanoparticle, surfactant and polymer in the presence of NaCl</title><secondary-title>Geosystem Engineering</secondary-title></titles><periodical><full-title>Geosystem Engineering</full-title></periodical><pages>195-205</pages><volume>17</volume><number>3</number><dates><year>2014</year></dates><isbn>1226-9328</isbn><urls></urls></record></Cite><Cite><Author>Ding</Author><Year>2018</Year><RecNum>101</RecNum><record><rec-number>101</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525938012″>101</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Ding, Yanan</author><author>Zheng, Sixu</author><author>Meng, Xiaoyan</author><author>Yang, Daoyong</author></authors></contributors><titles><title>Low Salinity Hot Water Injection with Addition of Nanoparticles for Enhancing Heavy Oil Recovery under Reservoir Conditions</title><secondary-title>SPE Western Regional Meeting</secondary-title></titles><dates><year>2018</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613995997</isbn><urls></urls></record></Cite></EndNote>149, 150.

5.5. Injection sequence
Alternating water with nanofluids has been found to enhance oil recovery compared to continuous nanofluids injection. This has been attributed to the water which is injected alternatively with the nanofluids, preventing the agglomeration of the nanoparticles that could plug the cores. Teng et al ADDIN EN.CITE <EndNote><Cite><Author>Lu</Author><Year>2017</Year><RecNum>99</RecNum><DisplayText>147</DisplayText><record><rec-number>99</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525937543″>99</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Lu, Teng</author><author>Li, Zhaomin</author><author>Zhou, Yan</author><author>Zhang, Chao</author></authors></contributors><titles><title>Enhanced oil recovery of low-permeability cores by SiO2 nanofluid</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>5612-5621</pages><volume>31</volume><number>5</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>147 conducted 3 runs using different pore volumes as shown in Figure 10. As seen, oil recovery increased as the injection cycles increased for runs 3, 9 and 10, respectively.

4034028-2729992(b)
00(b)
1446149-2834640(a)
00(a)
Figure 10. On the left (a) is the schematic diagram of different tested injection schemes and on the (b) is tertiary oil recovery rates for the selected runs modified from ADDIN EN.CITE <EndNote><Cite><Author>Lu</Author><Year>2017</Year><RecNum>99</RecNum><DisplayText>147</DisplayText><record><rec-number>99</rec-number><foreign-keys><key app=”EN” db-id=”zfzze9wzrtfssnexszmpft25av9wvxwzpez9″ timestamp=”1525937543″>99</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Lu, Teng</author><author>Li, Zhaomin</author><author>Zhou, Yan</author><author>Zhang, Chao</author></authors></contributors><titles><title>Enhanced oil recovery of low-permeability cores by SiO2 nanofluid</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>5612-5621</pages><volume>31</volume><number>5</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>147.

5.6. Effect of the Temperature
Temperature is an important parameter that affects the rheology of the produced fluids. Higher temperatures are significant in reducing oil viscosity and interfacial tension (IFT), which can improve the oil sweep and displacement efficiency. Esfandyari et al ADDIN EN.CITE <EndNote><Cite><Author>Esfandyari Bayat</Author><Year>2014</Year><RecNum>62</RecNum><DisplayText>39</DisplayText><record><rec-number>62</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>62</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Esfandyari Bayat, Ali</author><author>Junin, Radzuan</author><author>Samsuri, Ariffin</author><author>Piroozian, Ali</author><author>Hokmabadi, Mehrdad</author></authors></contributors><titles><title>Impact of Metal Oxide Nanoparticles on Enhanced Oil Recovery from Limestone Media at Several Temperatures</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>6255-6266</pages><volume>28</volume><number>10</number><dates><year>2014</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef5013616</electronic-resource-num></record></Cite></EndNote>39 dispersed three different nanofluids at different temperatures of 26,40,50 and 60 oC. The results showed that there was a higher tertiary recovery for all the different nanoparticles at 60 oC, while 26 oC gave the lowest oil recovery as shown in Figure 11.

Figure 11. Oil recovery via Al2O3, TiO2, and SiO2 nanofluids at different temperatures after brine flooding ADDIN EN.CITE <EndNote><Cite><Author>Esfandyari Bayat</Author><Year>2014</Year><RecNum>62</RecNum><DisplayText>39</DisplayText><record><rec-number>62</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>62</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Esfandyari Bayat, Ali</author><author>Junin, Radzuan</author><author>Samsuri, Ariffin</author><author>Piroozian, Ali</author><author>Hokmabadi, Mehrdad</author></authors></contributors><titles><title>Impact of Metal Oxide Nanoparticles on Enhanced Oil Recovery from Limestone Media at Several Temperatures</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>6255-6266</pages><volume>28</volume><number>10</number><dates><year>2014</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef5013616</electronic-resource-num></record></Cite></EndNote>39.

This increment in oil recovery after brine injection was attributed to both the decrease of the contact angle and IFT in the presence of different nanofluids as the temperatures decreased (Figure 12). From these figures, at 26 oC there was no significant change for both contact angle and IFT for either type of the nanoparticles used; both the contact angle and IFT reduced as the temperature increased which resulted into improvement in displacement efficiency resulting in additional oil recovery.

Figure 12. Effect of temperature on IFT (a) and contact angle (b) ADDIN EN.CITE <EndNote><Cite><Author>Esfandyari Bayat</Author><Year>2014</Year><RecNum>62</RecNum><DisplayText>39</DisplayText><record><rec-number>62</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>62</key><key app=”ENWeb” db-id=””>0</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Esfandyari Bayat, Ali</author><author>Junin, Radzuan</author><author>Samsuri, Ariffin</author><author>Piroozian, Ali</author><author>Hokmabadi, Mehrdad</author></authors></contributors><titles><title>Impact of Metal Oxide Nanoparticles on Enhanced Oil Recovery from Limestone Media at Several Temperatures</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>6255-6266</pages><volume>28</volume><number>10</number><dates><year>2014</year></dates><isbn>0887-0624 1520-5029</isbn><urls></urls><electronic-resource-num>10.1021/ef5013616</electronic-resource-num></record></Cite></EndNote>39.
6. Concerns and uncertainties of using nanotechnology in enhancing oil recoveryAlthough nanotechnology contributes tremendously to technological advancement in many applications and is attracting attention for possible applications in medicine, health, agriculture, and energy industries, there are still some pending critical challenges ADDIN EN.CITE <EndNote><Cite><Author>Kahan</Author><Year>2009</Year><RecNum>85</RecNum><DisplayText>151</DisplayText><record><rec-number>85</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>85</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Kahan, Dan M</author><author>Rejeski, David</author></authors></contributors><titles><title>PRoject on emeRging nanotechnologies</title></titles><dates><year>2009</year></dates><urls></urls></record></Cite></EndNote>151. It has been conceptualized as an environmentally friendly technique over the last decade and many indirect and direct applications for nanomaterials are being used in the marketplace. However, there is minimal data on the nanometric effect of nanoparticles on human health and the environment due to limited filed applications ADDIN EN.CITE <EndNote><Cite><Author>Kahan</Author><Year>2009</Year><RecNum>85</RecNum><DisplayText>151</DisplayText><record><rec-number>85</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>85</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Kahan, Dan M</author><author>Rejeski, David</author></authors></contributors><titles><title>PRoject on emeRging nanotechnologies</title></titles><dates><year>2009</year></dates><urls></urls></record></Cite></EndNote>151. Premature studies revealed some concerns about the effect of nanomaterials ADDIN EN.CITE <EndNote><Cite><Author>Nel</Author><Year>2006</Year><RecNum>276</RecNum><DisplayText>152</DisplayText><record><rec-number>276</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>276</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nel, Andre</author><author>Xia, Tian</author><author>Mädler, Lutz</author><author>Li, Ning</author></authors></contributors><titles><title>Toxic potential of materials at the nanolevel</title><secondary-title>science</secondary-title></titles><periodical><full-title>science</full-title></periodical><pages>622-627</pages><volume>311</volume><number>5761</number><dates><year>2006</year></dates><isbn>0036-8075</isbn><urls></urls></record></Cite></EndNote>152. Associated benefits of nanoparticles from the environmental perspective are combined with challenges that may be difficult to predict. In addition, there is little information about the disposal, manufacturing, usage and any associated risk in the exposure to nanomaterials ADDIN EN.CITE <EndNote><Cite><Author>Powers</Author><Year>2006</Year><RecNum>87</RecNum><DisplayText>153</DisplayText><record><rec-number>87</rec-number><foreign-keys><key app=”EN” db-id=”ted55ds9ftvpp9ew29svtrez2zw2as00vsw5″>87</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Powers, Kevin W</author><author>Brown, Scott C</author><author>Krishna, Vijay B</author><author>Wasdo, Scott C</author><author>Moudgil, Brij M</author><author>Roberts, Stephen M</author></authors></contributors><titles><title>Research strategies for safety evaluation of nanomaterials. Part VI. Characterization of nanoscale particles for toxicological evaluation</title><secondary-title>Toxicological Sciences</secondary-title></titles><periodical><full-title>Toxicological Sciences</full-title></periodical><pages>296-303</pages><volume>90</volume><number>2</number><dates><year>2006</year></dates><isbn>1096-6080</isbn><urls></urls></record></Cite></EndNote>153. As it is known, nanomaterials based on their dimensions, shapes and surface energy, they match with some of the biological body molecules such as proteins or nucleic acids. Hence when nanomaterials come in contact with the fluids of the body, they can be adsorbed easily. These adsorbed materials may spread to the target sites such as the heart, liver or blood cells and cause damage ADDIN EN.CITE <EndNote><Cite><Author>Purohit</Author><Year>2017</Year><RecNum>275</RecNum><DisplayText>154</DisplayText><record><rec-number>275</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>275</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Purohit, Rajesh</author><author>Mittal, Aman</author><author>Dalela, Srajan</author><author>Warudkar, Vilas</author><author>Purohit, Kiran</author><author>Purohit, Surabhi</author></authors></contributors><titles><title>Social, Environmental and Ethical Impacts of Nanotechnology</title><secondary-title>Materials Today: Proceedings</secondary-title></titles><periodical><full-title>Materials Today: Proceedings</full-title></periodical><pages>5461-5467</pages><volume>4</volume><number>4</number><dates><year>2017</year></dates><isbn>2214-7853</isbn><urls></urls></record></Cite></EndNote>154. However, studies have shown that remediation management and control of nanomaterials can reduce their environmental and health hazards ADDIN EN.CITE <EndNote><Cite><Author>Purohit</Author><Year>2017</Year><RecNum>275</RecNum><DisplayText>154</DisplayText><record><rec-number>275</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>275</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Purohit, Rajesh</author><author>Mittal, Aman</author><author>Dalela, Srajan</author><author>Warudkar, Vilas</author><author>Purohit, Kiran</author><author>Purohit, Surabhi</author></authors></contributors><titles><title>Social, Environmental and Ethical Impacts of Nanotechnology</title><secondary-title>Materials Today: Proceedings</secondary-title></titles><periodical><full-title>Materials Today: Proceedings</full-title></periodical><pages>5461-5467</pages><volume>4</volume><number>4</number><dates><year>2017</year></dates><isbn>2214-7853</isbn><urls></urls></record></Cite></EndNote>154. Less exposure to nanomaterials and using respirators has been suggested as a way of diminishing nanoparticles inhalation that may result in respiratory irritation and damage to body organs ADDIN EN.CITE <EndNote><Cite><Author>Nel</Author><Year>2006</Year><RecNum>276</RecNum><DisplayText>152</DisplayText><record><rec-number>276</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>276</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nel, Andre</author><author>Xia, Tian</author><author>Mädler, Lutz</author><author>Li, Ning</author></authors></contributors><titles><title>Toxic potential of materials at the nanolevel</title><secondary-title>science</secondary-title></titles><periodical><full-title>science</full-title></periodical><pages>622-627</pages><volume>311</volume><number>5761</number><dates><year>2006</year></dates><isbn>0036-8075</isbn><urls></urls></record></Cite></EndNote>152. Titanium, nickle and CNTs, cobalt, polystyrene, and latex have been postulated as examples of nanoparticles responsible for respiratory toxicity compared to quartz nanomaterials ADDIN EN.CITE <EndNote><Cite><Author>Purohit</Author><Year>2017</Year><RecNum>275</RecNum><DisplayText>154</DisplayText><record><rec-number>275</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>275</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Purohit, Rajesh</author><author>Mittal, Aman</author><author>Dalela, Srajan</author><author>Warudkar, Vilas</author><author>Purohit, Kiran</author><author>Purohit, Surabhi</author></authors></contributors><titles><title>Social, Environmental and Ethical Impacts of Nanotechnology</title><secondary-title>Materials Today: Proceedings</secondary-title></titles><periodical><full-title>Materials Today: Proceedings</full-title></periodical><pages>5461-5467</pages><volume>4</volume><number>4</number><dates><year>2017</year></dates><isbn>2214-7853</isbn><urls></urls></record></Cite></EndNote>154. There is a need to create ethical related issues, test protocols and prcedures that will guarantee safe handling of nanomaterials for EOR field applications. Currently, there are several agencies that have started the health access and environmental safety inspection of nanoparticles and have developed precautions. For example in the United States, agencies such as, National Toxicology Program (NTP) National Center for Environmental Research of the Environmental Protection Agency (EPA), National Institute of Occupational Safety and Health (NIOSH), National Institute of Environmental Health have all been commissioned for application and risk assessment of nanomaterials ADDIN EN.CITE <EndNote><Cite><Author>Nel</Author><Year>2006</Year><RecNum>276</RecNum><DisplayText>152</DisplayText><record><rec-number>276</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>276</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nel, Andre</author><author>Xia, Tian</author><author>Mädler, Lutz</author><author>Li, Ning</author></authors></contributors><titles><title>Toxic potential of materials at the nanolevel</title><secondary-title>science</secondary-title></titles><periodical><full-title>science</full-title></periodical><pages>622-627</pages><volume>311</volume><number>5761</number><dates><year>2006</year></dates><isbn>0036-8075</isbn><urls></urls></record></Cite></EndNote>152. In summery as a recommendation to nanoparticle users, less exposure to nanomaterials and using respirators has been suggested as a way of diminishing nanoparticles inhalation that may result in respiratory irritation and damage to other body organs ADDIN EN.CITE <EndNote><Cite><Author>Nel</Author><Year>2006</Year><RecNum>276</RecNum><DisplayText>152</DisplayText><record><rec-number>276</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>276</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nel, Andre</author><author>Xia, Tian</author><author>Mädler, Lutz</author><author>Li, Ning</author></authors></contributors><titles><title>Toxic potential of materials at the nanolevel</title><secondary-title>science</secondary-title></titles><periodical><full-title>science</full-title></periodical><pages>622-627</pages><volume>311</volume><number>5761</number><dates><year>2006</year></dates><isbn>0036-8075</isbn><urls></urls></record></Cite></EndNote>152.7. Opportunities and challenges
Nanomaterials have various applications in the oil and gas industry. With continued research, technology, and development, the prospect of their application in the oil and gas industry is very promising. However, the application of nanomaterials currently is limited to laboratory scale with very few field applications reported. The major challenge as to why many promising results are limited to only laboratory scale is the cost of the nanoparticles and lack of clear and simple synthesis protocols that offer pathways for scalability and commercial applications. When scaling-up, always technical and economic problems arise; thus, only a fraction of the laboratory nanomaterials can be saved. Other challenges that need to be addressed while proposing and developing such materials include the uniqueness of the material compared to those that already exist, regeneration ability, competitiveness with the existing material in the market in terms of adaptability and application. Nevertheless, the nanomaterial should have simple preparation pathways that offer options for scalability. Otherwise, the proposed materials must be better somehow than the existing conventional chemicals used in EOR or at least provide better advantages than the competitor or, introduce a new necessity or technique, a process not covered by any previously developed materials more important at low cost while minimizing the risk. Besides, most of the researchers that have been successful in developing these new promising nanomaterials lack industrial patterners, have no business plans and lack scale-up expertise which limits the process. It is important to note that not all new developed and promising materials end up being scaled up and commercialized. Successful scale-up and commercialization of developed materials are always associated with an important process of delivering a huge benefit for a company, corporation or government. Early detection of industrial partners is an important key for the development of a material for commercial scale. Lastly, cost analysis of nanoparticles to back up the experimental findings and evidence is further needed. The analysis of costs involved should be based on the crude oil prices in the world markets and also compared with the cost of the conventional EOR agents commonly used such as surfactants, polymers and alkaline. This will guarantee the economic viability of nanoparticles as EOR alternatives now or later.

8. Conclusions and future outlookIn conclusion, nanoparticles have a great potential of changing the perspective of the oil and gas industry in many aspects. Presently, researchers have evidence that nanoparticles can be used in various sectors of oil and gas ranging from exploration, production to refinery. In this review, we have explored some of the common types of nanoparticles used in enhancing oil recovery, their underlying mechanisms and operating parameters that control the oil recovery with NANO-EOR. Also, for the applicability of nanofluids in oil recovery, stabilization techniques recommended for NANO-EOR have been reviewed. However, there is a need to develop, synthesis pathways that are more cost-effective, efficient and offer options for scalability to allow nanoparticles to be integrated into oil recovery systems. Such nanoparticles should be easily adaptable and sustainable both to the users and the environment. Most of the previous studies have focused on using isotropic (homogenous) nanoparticles and fewer studies have been done with anisotropic types of nanomaterials in oil recovery enhancement. Hence, there is a need to investigate also the anisotropic nanoparticles that have asymmetrical or double face properties that mimic the commonly used surfactants in recovering residual oil. Because of the synergistic abilities for both the surfactant and the nanoparticles, we expect that proposed anisotropic nanomaterials may perform better compared to the existing commonly used isotropic nanoparticles. Also, many studies regarding NANO-EOR have reported promising results but under ambient conditions. Therefore, similar studies of NANO-EOR are still needed to enhance their adaptability for pilot and field applications most especially at reservoir conditions.

Acknowledgements
The authors are grateful to the Natural Sciences and Engineering Research Council of Canada (NSERC) for the financial support provided through the NSERC Industrial Research Chair in Catalysis for Bitumen Upgrading. Also, the contribution of facilities from the Schulich School of Engineering and the Faculty of Science at the University of Calgary are greatly appreciated.
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Type and size Conditions Reservoir type Fluid properties Mechanism of recovery Remarks/conclusion Reference
Silica(20nm) coated with a zwitterionic polymer Ambient conditions Sandstone (Berea)
Ø (17%)
-Nanofluids 45wt%
DIW -IFT reduction
-Structural disjoining pressure
-Wettability alteration -Modified silica could reduce the oil water IFT more than the unmodified
-Coated silica improved oil recovery by 5 vol % ADDIN EN.CITE <EndNote><Cite><Author>Choi</Author><Year>2017</Year><RecNum>227</RecNum><DisplayText>155</DisplayText><record><rec-number>227</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>227</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Choi, Sang Koo</author><author>Son, Han Am</author><author>Kim, Hyun Tae</author><author>Kim, Jin Woong</author></authors></contributors><titles><title>Nanofluid enhanced oil recovery using hydrophobically associative zwitterionic polymer-coated silica nanoparticles</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>7777-7782</pages><volume>31</volume><number>8</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>155
Silica (7nm)
No surface modification Ambient conditions Sandstone (Berea)
Ø (15-22%)
K (9-400 mD) Oil 5.01 cP
-Brine (3.0 wt%)
-Nanofluids (0.01-0.1 wt%) -Wettability alteration
Increasing NP concentration reduced IFT -Higher NP concentration reduce IFT but no additional oil because of pore blockage.

-Optimal nanofluid concentration is required for additional recovery. ADDIN EN.CITE <EndNote><Cite><Author>Hendraningrat</Author><Year>2013</Year><RecNum>92</RecNum><DisplayText>14</DisplayText><record><rec-number>92</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>92</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hendraningrat, Luky</author><author>Li, Shidong</author><author>Torsæter, Ole</author></authors></contributors><titles><title>A coreflood investigation of nanofluid enhanced oil recovery</title><secondary-title>Journal of Petroleum Science and Engineering</secondary-title></titles><periodical><full-title>Journal of Petroleum Science and Engineering</full-title></periodical><pages>128-138</pages><volume>111</volume><dates><year>2013</year></dates><isbn>0920-4105</isbn><urls></urls></record></Cite></EndNote>14
Silica (20nm)
No surface modification Ambient pressure and Temperature 55 0C Sandstone (Berea)
Ø (20%)
K (400 mD) -Oil viscosity 98.88 cP
-Brine 20,000 ppm
-Nanofluids 10 vol% silica -Wettability alteration
-No noticeable IFT reduction
-Structural disjoining pressure mechanism was verified using the formulated fluids.

-55% oil was recovered by silica nanofluid compared to only 2% recovered with pH 9.7 deionized water ADDIN EN.CITE <EndNote><Cite><Author>Zhang</Author><Year>2014</Year><RecNum>96</RecNum><DisplayText>48</DisplayText><record><rec-number>96</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>96</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Zhang, Hua</author><author>Nikolov, Alex</author><author>Wasan, Darsh</author></authors></contributors><titles><title>Enhanced oil recovery (EOR) using nanoparticle dispersions: underlying mechanism and imbibition experiments</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3002-3009</pages><volume>28</volume><number>5</number><dates><year>2014</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>48
Silica (7nm)
No surface modification Pressure 1450 psi and (25-80) 0C Sandstone (Berea)
Ø (15-19%)
K (100-600 mD) -Oil viscosity 5.1 cP
-Brine 3wt %
-Nanofluids 0.05 wt % -Wettability alteration
-no significant IFT reduction -More oil was recovered from all wettability system at high temperature.

-Initial wettability of rock affects waterflood behavior and oil recovery.

Optimal nano-EOR was achieved in intermediate system.

-Noticeable NP aggregation led to pressure jamming especially at high temperatures.

ADDIN EN.CITE <EndNote><Cite><Author>Hendraningrat</Author><Year>2014</Year><RecNum>91</RecNum><DisplayText>156</DisplayText><record><rec-number>91</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>91</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hendraningrat, Luky</author><author>Torsæter, Ole</author></authors></contributors><titles><title>Effects of the initial rock wettability on silica-based nanofluid-enhanced oil recovery processes at reservoir temperatures</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>6228-6241</pages><volume>28</volume><number>10</number><dates><year>2014</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>156
Silica (<40nm)
No surface modification Ambient pressure Temperature 50 0C Sandstone (Berea)
Ø (9.35-11.95%)
K (0.68-0.95 mD) Oil 20.9 Cp
-Brine (7500 ppm)
-Nanofluid (5-30 ppm) -Wettability alteration
-Viscosity reduction by increasing nanoparticle concentration -After nanoparticle adsorption there was noticeable increase in irreducible water saturation and Kro.

-Additional 4.48-10.33% oil was recovered after silica nanofluid injection.

Optimum nanoconcentrations was 10ppm.

-Increasing nanoparticle concentration reduced the oil viscosity and asphaltene content.

-Lower injection rates are proposed for optimized recovery. ADDIN EN.CITE <EndNote><Cite><Author>Lu</Author><Year>2017</Year><RecNum>95</RecNum><DisplayText>147</DisplayText><record><rec-number>95</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>95</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Lu, Teng</author><author>Li, Zhaomin</author><author>Zhou, Yan</author><author>Zhang, Chao</author></authors></contributors><titles><title>Enhanced oil recovery of low-permeability cores by SiO2 nanofluid</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>5612-5621</pages><volume>31</volume><number>5</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>147
Silica (10nm)
Surface modified with hexanedioic acid
Silica (20nm)
No surface modification Ambient pressure Temperature 60 0C
Ambient conditions Sandstone (Berea)
Ø (14%)
K (0.6mD)
Sandstone (Berea)
Ø (19%)
K (587mD) -Oil 2.02 Cp
-Brine (3 wt %)
-Nanofluid (0.001-1 wt%)
Nanofluid (0.01-0.5wt%)
-Oil 4.6 Cp
-Brine (3 wt% NaCl) -Wettability alteration and IFT reduction
Wettability alteration and IFT reduction -Silica surface was modified to obtain active silica that performed better than conventional silica.

-silica NP showed good oil displacement properties.

-Great potential of using active silica for EOR free from surfactants.

-Silica NPs environmentally compatible with sandstone
-Additional 13% recovered during silica injection
-Low injection rates reduce permeability impairment.

-Silica NPs delay water breakthrough ADDIN EN.CITE <EndNote><Cite><Author>Li</Author><Year>2017</Year><RecNum>86</RecNum><DisplayText>157</DisplayText><record><rec-number>86</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>86</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Li, Yuyang</author><author>Dai, Caili</author><author>Zhou, Hongda</author><author>Wang, Xinke</author><author>Lv, Wenjiao</author><author>Zhao, Mingwei</author></authors></contributors><titles><title>Investigation of spontaneous imbibition by using a surfactant-free active silica water-based nanofluid for enhanced oil recovery</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>157
ADDIN EN.CITE <EndNote><Cite><Author>Youssif</Author><Year>2017</Year><RecNum>209</RecNum><DisplayText>158</DisplayText><record><rec-number>209</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>209</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Youssif, Magda I</author><author>El-Maghraby, Rehab M</author><author>Saleh, Sayed M</author><author>Elgibaly, Ahmed</author></authors></contributors><titles><title>Silica nanofluid flooding for enhanced oil recovery in sandstone rocks</title><secondary-title>Egyptian Journal of Petroleum</secondary-title></titles><periodical><full-title>Egyptian Journal of Petroleum</full-title></periodical><dates><year>2017</year></dates><isbn>1110-0621</isbn><urls></urls></record></Cite></EndNote>158
Silica (5-15nm)
No surface modification Ambient conditions Carbonate (chalk)
Properties not mentioned n- decane
-Brine (0-20wt%)
-Nanofluids (0.5-4wt%) -Wettability alteration -Exposure time of nanofluids effects rate of wettability alteration.

-Nanoparticle adsorption was confirmed to be an irreversible process. ADDIN EN.CITE <EndNote><Cite><Author>Al-Anssari</Author><Year>2016</Year><RecNum>89</RecNum><DisplayText>159</DisplayText><record><rec-number>89</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>89</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Al-Anssari, Sarmad</author><author>Barifcani, Ahmed</author><author>Wang, Shaobin</author><author>Maxim, Lebedev</author><author>Iglauer, Stefan</author></authors></contributors><titles><title>Wettability alteration of oil-wet carbonate by silica nanofluid</title><secondary-title>Journal of colloid and interface science</secondary-title></titles><periodical><full-title>Journal of colloid and interface science</full-title></periodical><pages>435-442</pages><volume>461</volume><dates><year>2016</year></dates><isbn>0021-9797</isbn><urls></urls></record></Cite></EndNote>159
-Silica (7nm)
-Surface modified with Benzimidazole Ambient pressure Temperature 80 0C Sandstone (Berea)
Ø (20%)
K (54mD) Oil 5.0 Cp
Brine (5 wt %)
Nanofluid (1wt%) -Wettability alteration
-No significant IFT reduction -Structural disjoining force was the major mechanism for wettability alteration
-Additional 38% oil was recovered by 0.1 wt % nanofluids after 10 days.

-Surface modification resulted in less particle aggregation. ADDIN EN.CITE <EndNote><Cite><Author>Dai</Author><Year>2017</Year><RecNum>88</RecNum><DisplayText>141</DisplayText><record><rec-number>88</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>88</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Dai, Caili</author><author>Wang, Xinke</author><author>Li, Yuyang</author><author>Lv, Wenjiao</author><author>Zou, Chenwei</author><author>Gao, Mingwei</author><author>Zhao, Mingwei</author></authors></contributors><titles><title>Spontaneous imbibition investigation of self-dispersing silica nanofluids for enhanced oil recovery in low-permeability cores</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2663-2668</pages><volume>31</volume><number>3</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>141
Silica (8nm)
Ambient conditions NA (batch study) -Oil viscosity 120000 & 2200000 cp
Distilled water
-Nanofluids 10-10000 ppm)
-Viscosity reduction
-No significant IFT reduction
-Silica (8nm) nano particles yielded the best viscosity reduction at 1000ppm.

Oil viscosity reduction increases as the NP size increase.

ADDIN EN.CITE <EndNote><Cite><Author>Taborda</Author><Year>2017</Year><RecNum>90</RecNum><DisplayText>160</DisplayText><record><rec-number>90</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>90</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Taborda, Esteban A</author><author>Franco, Camilo A</author><author>Ruiz, Marco A</author><author>Alvarado, Vladimir</author><author>Corte?s, Farid B</author></authors></contributors><titles><title>Experimental and theoretical study of viscosity reduction in heavy crude oils by addition of nanoparticles</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1329-1338</pages><volume>31</volume><number>2</number><dates><year>2017</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>160
ZnO(31-36nm) Ambient conditions Packed glass beads Nanofluids 0.05-0.5wt% IFT reduction -highest recovery factor of 11.82% at 0.3 wt% is due to the oil/water interfacial tension reduction and wettability alteration. ADDIN EN.CITE <EndNote><Cite><Author>Soleimani</Author><Year>2018</Year><RecNum>242</RecNum><DisplayText>161</DisplayText><record><rec-number>242</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>242</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Soleimani, Hassan</author><author>Baig, Mirza Khurram</author><author>Yahya, Noorhana</author><author>Khodapanah, Leila</author><author>Sabet, Maziyar</author><author>Demiral, Birol MR</author><author>Burda, Marek</author></authors></contributors><titles><title>Synthesis of ZnO nanoparticles for oil–water interfacial tension reduction in enhanced oil recovery</title><secondary-title>Applied Physics A</secondary-title></titles><periodical><full-title>Applied Physics A</full-title></periodical><pages>128</pages><volume>124</volume><number>2</number><dates><year>2018</year></dates><isbn>0947-8396</isbn><urls></urls></record></Cite></EndNote>161
ZrO2 Ambient pressure and Temperature 70 0C Carbonate
Ø (20%)
K (30 mD) -Oil viscosity 64 cts-distilled water
-Nanofluids 5 wt % Wettability alteration ZrO2 nanofluids are wettability modifiers for carbonate systems.

-Wettability change by adsorption and growth of ZrO2 nanoparticles on the rock surface was a slow process, requiring at least 2 days.

– Free imbibition tests revealed strong capability for oil recovery.

ADDIN EN.CITE <EndNote><Cite><Author>Karimi</Author><Year>2012</Year><RecNum>98</RecNum><DisplayText>74</DisplayText><record><rec-number>98</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>98</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Karimi, Ali</author><author>Fakhroueian, Zahra</author><author>Bahramian, Alireza</author><author>Pour Khiabani, Nahid</author><author>Darabad, Jabar Babaee</author><author>Azin, Reza</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Wettability alteration in carbonates using zirconium oxide nanofluids: EOR implications</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>1028-1036</pages><volume>26</volume><number>2</number><dates><year>2012</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>74
Al2O3(40nm)
Ambient pressure and temperature 70 0C Carbonate (chalk)
Ø (12.2-14.2%)
K (0.3-0.13mD) Oil 64 Cp
Brine 30000 ppm
Nanofluids (5wt%) Wettability alteration CaCO3 and SiO2 behaved in acceptable way based on the generalized fitting of a water wet system.

Oil recovery increase in presence of CaCO3 and SiO2 by a factor of 4 and 6 respectively.

ADDIN EN.CITE <EndNote><Cite><Author>Nazari Moghaddam</Author><Year>2015</Year><RecNum>93</RecNum><DisplayText>55</DisplayText><record><rec-number>93</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>93</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nazari Moghaddam, Rasoul</author><author>Bahramian, Alireza</author><author>Fakhroueian, Zahra</author><author>Karimi, Ali</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Comparative study of using nanoparticles for enhanced oil recovery: wettability alteration of carbonate rocks</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2111-2119</pages><volume>29</volume><number>4</number><dates><year>2015</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>55
ZrO2(35nm), CaCO3(spherical), TiO2(35nm) SiO2 and CNT (tubes), MgO (40nm), Al2O3(40nm), CeO2(bar shape)
-No surface modifications Ambient pressure and temperature 70 0C Carbonate (chalk)
Ø (12.2-14.2%)
K (0.3-0.13mD) Oil 64 Cp
Brine 30000 ppm
Nanofluids (5wt%) Wettability alteration CaCO3 and SiO2 behaved in acceptable way based on the generalized fitting of a water wet system.

Oil recovery increase in presence of CaCO3 and SiO2 by a factor of 4 and 6 respectively.

ADDIN EN.CITE <EndNote><Cite><Author>Nazari Moghaddam</Author><Year>2015</Year><RecNum>93</RecNum><DisplayText>55</DisplayText><record><rec-number>93</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>93</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nazari Moghaddam, Rasoul</author><author>Bahramian, Alireza</author><author>Fakhroueian, Zahra</author><author>Karimi, Ali</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Comparative study of using nanoparticles for enhanced oil recovery: wettability alteration of carbonate rocks</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2111-2119</pages><volume>29</volume><number>4</number><dates><year>2015</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>55
Aluminum oxide (40nm)
Silica (20nm)
Titanium di0xide(10-30nm)
No surface modification Ambient pressure
Temperatures (25-60) 0C Carbonate (Limestone)
Ø (43%)
K (3.12 D) degassed crude 21.7 Cp
Brine 2.5wt %
Nanofluid 0.005 wt % Wettability alteration
Viscosity reduction
IFT reduction
Capillary force reduction -In terms of adsorption Al2O3 had the lowest 8.2 %, TiO2 27.8%, and SiO2 43.4% and was related to surface charge.- Al2O3 performed better in limestone medium followed by TiO2, and then SiO2.

-All NP shifted wettability from intermediate to strong water wet
ADDIN EN.CITE <EndNote><Cite><Author>Esfandyari Bayat</Author><Year>2014</Year><RecNum>20</RecNum><DisplayText>39</DisplayText><record><rec-number>20</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>20</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Esfandyari Bayat, Ali</author><author>Junin, Radzuan</author><author>Samsuri, Ariffin</author><author>Piroozian, Ali</author><author>Hokmabadi, Mehrdad</author></authors></contributors><titles><title>Impact of metal oxide nanoparticles on enhanced oil recovery from limestone media at several temperatures</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>6255-6266</pages><volume>28</volume><number>10</number><dates><year>2014</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>39
Al2O3 (21nm) Ambient conditions Sandstone (Berea)
Ø (20%)
K (54mD) -Oil viscosity 5.1 cp
-0.05 wt %
Brine 3 wt % IFT reduction
-Wettability alteration
Viscosity reduction -Stability of nanoparticles was improved by adding 1 wt % polyvinylpyrrolidone (PVP)
ADDIN EN.CITE <EndNote><Cite><Author>Hendraningrat</Author><Year>2015</Year><RecNum>217</RecNum><DisplayText>57</DisplayText><record><rec-number>217</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>217</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Hendraningrat, Luky</author><author>Torsæter, Ole</author></authors></contributors><titles><title>Metal oxide-based nanoparticles: revealing their potential to enhance oil recovery in different wettability systems</title><secondary-title>Applied Nanoscience</secondary-title></titles><periodical><full-title>Applied Nanoscience</full-title></periodical><pages>181-199</pages><volume>5</volume><number>2</number><dates><year>2015</year></dates><isbn>2190-5509</isbn><urls></urls></record></Cite></EndNote>57
Al2O3 (21nm) Ambient conditions Sand pack
-Oil viscosity 5 cp
-brine (30g/l)
-Wettability alteration,
-IFT reduction,
-Reduction of oil viscosity reduction of mobility ratio permeability alterations – produced oil from alumina oxide NPs was lighter than the injected oil
-ethanol can be used as a dispersing media for NPs
ADDIN EN.CITE <EndNote><Cite><Author>Ogolo</Author><Year>2012</Year><RecNum>218</RecNum><DisplayText>15</DisplayText><record><rec-number>218</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>218</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Ogolo, NA</author><author>Olafuyi, OA</author><author>Onyekonwu, MO</author></authors></contributors><titles><title>Enhanced oil recovery using nanoparticles</title><secondary-title>SPE Saudi Arabia section technical symposium and exhibition</secondary-title></titles><dates><year>2012</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613992300</isbn><urls></urls></record></Cite></EndNote>15
Aluminum oxide (35nm)
No surface modifications 2800 psi and
Temperature 50 0C Sandstone (Berea)
Ø (33%)
K (2.19 D) -Heavy oil 64 cP
-Distilled water
-Nanofluids (100-10000 ppm) Wettability alteration
IFT reduction -Nanoparticles were dispersed in SDS surfactant.

-Alumina based NP altered the wettability from strong oil wet to strong water wet.

-Effectiveness of anionic surfactant as wettability modifiers can be improved by adding alumina NP at low concentrations.

-Oil efficiency by water flooding in oil wet rocks can be enhanced by dispersing low alumina NP concentrations. ADDIN EN.CITE <EndNote><Cite><Author>Giraldo</Author><Year>2013</Year><RecNum>87</RecNum><DisplayText>17</DisplayText><record><rec-number>87</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>87</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Giraldo, Juliana</author><author>Benjumea, Pedro</author><author>Lopera, Sergio</author><author>Corte?s, Farid B</author><author>Ruiz, Marco A</author></authors></contributors><titles><title>Wettability alteration of sandstone cores by alumina-based nanofluids</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>3659-3665</pages><volume>27</volume><number>7</number><dates><year>2013</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>17
Al2O3(21nm) Ambient conditions Sandstone (Berea)
Ø (17%)
K (110mD) Brine 2.5wt %
Oil viscosity 40.38cp
Nanofluids (1-4) wt% -IFT reduction
-Wettability alteration – Al2O3 change the rock wettability from water wet to neutral wet state
-Aluminum oxide nanoparticles that are dispersed in propanol have more tendencies to enhance oil recovery ADDIN EN.CITE <EndNote><Cite><Author>Joonaki</Author><Year>2014</Year><RecNum>219</RecNum><DisplayText>162</DisplayText><record><rec-number>219</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>219</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Joonaki, E</author><author>Ghanaatian, S</author></authors></contributors><titles><title>The application of nanofluids for enhanced oil recovery: effects on interfacial tension and coreflooding process</title><secondary-title>Petroleum Science and Technology</secondary-title></titles><periodical><full-title>Petroleum Science and Technology</full-title></periodical><pages>2599-2607</pages><volume>32</volume><number>21</number><dates><year>2014</year></dates><isbn>1091-6466</isbn><urls></urls></record></Cite></EndNote>162
Al2O3(>40 nm) Ambient conditions carbonate
Ø (12.2-14.2%)
K (0.3-0.13mD) Brine 3wt% oil viscosity 2 cP -Wettability alteration -wettability of the rock surface changed to more water-wetting after injection of the nanofluids. ADDIN EN.CITE <EndNote><Cite><Author>Nazari Moghaddam</Author><Year>2015</Year><RecNum>220</RecNum><DisplayText>55</DisplayText><record><rec-number>220</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>220</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Nazari Moghaddam, Rasoul</author><author>Bahramian, Alireza</author><author>Fakhroueian, Zahra</author><author>Karimi, Ali</author><author>Arya, Sharareh</author></authors></contributors><titles><title>Comparative study of using nanoparticles for enhanced oil recovery: wettability alteration of carbonate rocks</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2111-2119</pages><volume>29</volume><number>4</number><dates><year>2015</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>55
alumina (?- (25 – 31nm) 290-325K
Ambient pressure NA Nanofluids
0.1-0.5wt %
DIW
toluene -IFT reduction
-Hydrophobically modified alumina NPs were more active in IFT reduction than the unmodified or hydrophilic alumina NPs ADDIN EN.CITE <EndNote><Cite><Author>Saien</Author><Year>2013</Year><RecNum>221</RecNum><DisplayText>163</DisplayText><record><rec-number>221</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>221</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Saien, Javad</author><author>Moghaddamnia, Farzaneh</author><author>Bamdadi, Hamid</author></authors></contributors><titles><title>Interfacial Tension of Methylbenzene–Water in the Presence of Hydrophilic and Hydrophobic Alumina Nanoparticles at Different Temperatures</title><secondary-title>Journal of Chemical &amp; Engineering Data</secondary-title></titles><periodical><full-title>Journal of Chemical &amp; Engineering Data</full-title></periodical><pages>436-440</pages><volume>58</volume><number>2</number><dates><year>2013</year></dates><isbn>0021-9568</isbn><urls></urls></record></Cite></EndNote>163
?- Al2O3(>40 nm) Ambient conditions Sand & carbonate media
Ø (42%)
K (2.03 D) Nanofluids
0.005wt %
Brine (NaCl
(0.3wt%) -IFT reduction
-Wettability alteration – Al2O3 has higher mobility in carbonates than in sandstones formation. ADDIN EN.CITE <EndNote><Cite><Author>Bayat</Author><Year>2015</Year><RecNum>222</RecNum><DisplayText>58</DisplayText><record><rec-number>222</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>222</key></foreign-keys><ref-type name=”Conference Proceedings”>10</ref-type><contributors><authors><author>Bayat, Ali Esfandyari</author><author>Junin, Radzuan</author></authors></contributors><titles><title>Transportation of metal oxide nanoparticles through various porous media for enhanced oil recovery</title><secondary-title>SPE/IATMI Asia Pacific Oil &amp; Gas Conference and Exhibition</secondary-title></titles><dates><year>2015</year></dates><publisher>Society of Petroleum Engineers</publisher><isbn>1613993900</isbn><urls></urls></record></Cite></EndNote>58
?- Al2O3(>40 nm) Ambient conditions Sand pack Nanofluids
0.1-1wt %
Brine (NaCl
DIW Foam enhancement -Additional 14% recovered with presence of Al2O3 nanoparticles. ADDIN EN.CITE <EndNote><Cite><Author>Manan</Author><Year>2015</Year><RecNum>225</RecNum><DisplayText>148</DisplayText><record><rec-number>225</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>225</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Manan, MA</author><author>Farad, S</author><author>Piroozian, A</author><author>Esmail, MJA</author></authors></contributors><titles><title>Effects of nanoparticle types on carbon dioxide foam flooding in enhanced oil recovery</title><secondary-title>Petroleum Science and Technology</secondary-title></titles><periodical><full-title>Petroleum Science and Technology</full-title></periodical><pages>1286-1294</pages><volume>33</volume><number>12</number><dates><year>2015</year></dates><isbn>1091-6466</isbn><urls></urls></record></Cite></EndNote>148
Alumina coated silica(20nm) Ambient conditions Berea sandstone
Ø (18-22%)
K (125-606mD) Nanofluids (0.05-1) wt%
Oil viscosity 30 cp
Foam stability -Irreversible adsorption of NPs on the air water interface resulted in foam stability
-70-75% additional oil was recovered ADDIN EN.CITE <EndNote><Cite><Author>Singh</Author><Year>2016</Year><RecNum>226</RecNum><DisplayText>164</DisplayText><record><rec-number>226</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>226</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Singh, Robin</author><author>Mohanty, Kishore K</author></authors></contributors><titles><title>Foams stabilized by in-situ surface-activated nanoparticles in bulk and porous media</title><secondary-title>SPE Journal</secondary-title></titles><periodical><full-title>SPE Journal</full-title></periodical><pages>121-130</pages><volume>21</volume><number>01</number><dates><year>2016</year></dates><isbn>1086-055X</isbn><urls></urls></record></Cite></EndNote>164
Nanocellulose 0.8-1.2 µm
No surface modification Ambient pressure and Temperature Micro glass model Oil 80.4 Cp
Brine 1 wt %
Nanofluid 0.005 wt % Nanocellulose improved the viscosity of the injected fluid
IFT reduction IN order of 10-1mN/m -Nanofluids showed superior thickening ability and pronounced shear thinning property.

– Sweep efficiency was improved.

Emulsification and entrainment were established during NC nanofluid flooding. ADDIN EN.CITE <EndNote><Cite><Author>Wei</Author><Year>2016</Year><RecNum>97</RecNum><DisplayText>88</DisplayText><record><rec-number>97</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>97</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Wei, Bing</author><author>Li, Qinzhi</author><author>Jin, Fayang</author><author>Li, Hao</author><author>Wang, Chongyang</author></authors></contributors><titles><title>The potential of a novel nanofluid in enhancing oil recovery</title><secondary-title>Energy &amp; Fuels</secondary-title></titles><periodical><full-title>Energy &amp; Fuels</full-title></periodical><pages>2882-2891</pages><volume>30</volume><number>4</number><dates><year>2016</year></dates><isbn>0887-0624</isbn><urls></urls></record></Cite></EndNote>88
Graphene-Based Amphiphilic Janus Ambient pressure and Temperature Berea sandstone
Ø (20-24%)
K (43.29-136.9mD) Oil 75 Cp
Brine 4 wt % NaCl and 1 wt % CaCl2
Nanofluid 0.01-0.005 wt % IFT reduction
-Wettability alteration ?7.5% increased oil recovery efficiency at ultralow concentration (0.005 wt %) ADDIN EN.CITE <EndNote><Cite><Author>Luo</Author><Year>2017</Year><RecNum>239</RecNum><DisplayText>165</DisplayText><record><rec-number>239</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>239</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Luo, Dan</author><author>Wang, Feng</author><author>Zhu, Jingyi</author><author>Tang, Lu</author><author>Zhu, Zhuan</author><author>Bao, Jiming</author><author>Willson, Richard C</author><author>Yang, Zhaozhong</author><author>Ren, Zhifeng</author></authors></contributors><titles><title>Secondary Oil Recovery Using Graphene-Based Amphiphilic Janus Nanosheet Fluid at an Ultralow Concentration</title><secondary-title>Industrial &amp; Engineering Chemistry Research</secondary-title></titles><periodical><full-title>Industrial &amp; Engineering Chemistry Research</full-title></periodical><pages>11125-11132</pages><volume>56</volume><number>39</number><dates><year>2017</year></dates><isbn>0888-5885</isbn><urls></urls></record></Cite></EndNote>165
MWCNT (20nm) Ambient pressure and temperature 60oC glass micromodels
(30- 60) µm Oil 75 Cp
Brine 4 wt % NaCl and 1 wt % CaCl2
Nanofluid 0.01-0.1 wt % -Wettability alteration -hydrophobic MWCNTs behaviour in water fluid is unpredictable
-highest recovery efficiency 31.8% of residual oil was achieved with the nanofluid of 0.05wt.% ADDIN EN.CITE <EndNote><Cite><Author>Alnarabiji</Author><Year>2016</Year><RecNum>240</RecNum><DisplayText>87</DisplayText><record><rec-number>240</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>240</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Alnarabiji, Mohamad Sahban</author><author>Yahya, Noorhana</author><author>Shafie, Afza</author><author>Solemani, Hassan</author><author>Chandran, Kayathiri</author><author>Hamid, Sharifah Bee Abd</author><author>Azizi, Khairun</author></authors></contributors><titles><title>The influence of hydrophobic multiwall carbon nanotubes concentration on enhanced oil recovery</title><secondary-title>Procedia engineering</secondary-title></titles><periodical><full-title>Procedia engineering</full-title></periodical><pages>1137-1140</pages><volume>148</volume><dates><year>2016</year></dates><isbn>1877-7058</isbn><urls></urls></record></Cite></EndNote>87
MWCNT Ambient pressure and Temperature glass bead sample Nanofluid 0.05-0.5 wt % IFT reduction
-Carbon nanotubes yield additional recovery of 18.57%
-Optimum concentration of MWCNT was 0.3 wt% ADDIN EN.CITE <EndNote><Cite><Author>Soleimani</Author><Year>2018</Year><RecNum>241</RecNum><DisplayText>166</DisplayText><record><rec-number>241</rec-number><foreign-keys><key app=”EN” db-id=”0xxrzwtviaee2beesrr5xwzs2xwptad9wpaf”>241</key></foreign-keys><ref-type name=”Journal Article”>17</ref-type><contributors><authors><author>Soleimani, Hassan</author><author>Baig, Mirza Khurram</author><author>Yahya, Noorhana</author><author>Khodapanah, Leila</author><author>Sabet, Maziyar</author><author>Demiral, Birol MR</author><author>Burda, Marek</author></authors></contributors><titles><title>Impact of carbon nanotubes based nanofluid on oil recovery efficiency using core flooding</title><secondary-title>Results in Physics</secondary-title></titles><periodical><full-title>Results in Physics</full-title></periodical><pages>39-48</pages><volume>9</volume><dates><year>2018</year></dates><isbn>2211-3797</isbn><urls></urls></record></Cite></EndNote>166

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