Site Loader

ASSESSMENT OF RESERVOIR QUALITY USING GAMMA RAY AND POROSITY LOGS OF SINJHORO GAS FIELD, LOWER INDUS BASIN, PAKISTAN

BY
MUJEEB UR REHMAN
CENTRE OF PURE AND APPLIED GEOLOGY UNIVERSITY OF SINDH
2018

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

ABSTRACT
The area under study is located near city of Tando Allahyar in Sanghar district, Sindh Province. Study area is present in the lower Indus Basin. This field was discovered by OGDCL in Sinjhoro Exploration Lease. Acquired seismic and well data for research project includes LAS files “CHAK63-01, CHAK66-01 and CHAK7A-01” for the wells namely “CHAK63-01, CHAK66-01 and CHAK7A-01”, well tops in soft copy. The reservoir assessment by using petrophysical logs and crossplots reveals that main lithology is sandstone. The hydrocarbons potential of the basal sand zone have been described through different total and effective porosity, volume of shale, and water and hydrocarbons saturation. The evaluated petrophysical studies show that the effective porosity range of to 10 to 16 %, volume of shale range of 30% to 40 % and hydrocarbon saturation range of 24 to 40 %. Overall assessment of reservoir shows that the basal sand zone has good potential of Hydrocarbons.

ACKNOWLEDGEMENTS
In the name of ALLAH, the most beneficent, the most merciful.
All praises to Almighty ALLAH, the creator of this universe. I bear witness that Holy Prophet Hazrat Muhammad (PBUH) is the last messenger. Without the blessings of ALLAH, I would not be able to complete my work as well as it is now.
I am especially indebted to my supervisor Mr. Fahad Mahmood (E&ES, BUIC) for giving me an initiative to this study. Their guidance, dynamic supervision and criticism for the betterment of this research project have helped me in completing my research project.
I would like to thank especially Head of the Department Dr. Muhammad Zafar and all the faculty member of Earth and Environmental Sciences Department for their assistance, cooperation, constructive criticism and guidance throughout my degree.
I also acknowledge the support, love, attention, care, prayers of my family and all my previous teachers which have always been a source of motivation for me.
I owe special thanks to Mr. M. Fahad Mahmood who critically reviewed this research work and endowed me with his precious time. I was fortunate to have his competent and devoted guidance which helped me to convert my thesis draft into this present manuscript.

CONTENTS
Page
ABSTRACT
ACKNOWLEDGEMENTS
CONTENTS
FIGURES
TABLES I
ii
iii
vi
viii

CHAPTER 1
INTRODUCTION
1.1 Location 1
1.2 Exploration history of the study area 2
1.3
1.3.1 Data Acquired
Well data 2
3
1.4 Objectives 3
CHAPTER 2
REGIONAL GEOLOGICAL FRAMEWORK OF STUDY AREA
2.1 Tectonics 4
2.2 Sedimentary Basins of Pakistan 4
2.2.1 Southern Indus Basin 6
2.3 Geology and tectonics of Sanghar/Sinjhoro block 8
2.4 Structural setting 9
2.5 Regional Stratigraphy 9
2.6
2.7
2.8 Stratigraphy of study area
Detailed stratigraphy of Formations of interest
Petroleum Geology of study area 10
11
12

CHAPTER 3
Methodology and Workflow
3.1 Wireline logs 14
3.2 Well Logging objectives 14
3.3 Types of well logging 14
3.4 Logs used for the study Of CHAK63-01, CHAK66-01 and CHAK7A-01 15
3.5
3.6 Petrophysical interpretation
Methodology adapted 17
17
CHAPTER 4
ASSESSMENT OF RESIRVOIR QUALITY IN CHAK63-01
4.1
4.2
4.3
4.4 Well related parameters
Borehole lithology of CHAK63-01 well
Selection of zone of interest
Volume of Shale calculation 21
22
22
24
4.5 Calculation of Effective Porosity in Reservoir Zone 25
4.6
4.7 Water Saturation in Reservoir Zone
Hydrocarbon Saturation in Reservoir Zone 26
27
4.8 Cross plots for identification of lithology 28
4.8.1
4.8.2 Sonic vs Density
Density vs Porosity 28
28
CHAPTER 5
ASSESSMENT OF RESIRVOIR QUALITY IN CHAK66-01
5.1 Well Related Parameters 31
5.2 Borehole lithology of CHAK66-01 well 32
5.3 Selection of zone of interest in borehole log 33
5.4 Volume of Shale calculation 34
5.5 Effective porosity in the reservoir zone 35
5.6 Saturation of Water in reservoir zone 36
5.7
5.8 Saturation of Hydrocarbons in reservoir zone
Cross plots for identification of lithology 37
38
5.8.1
5.8.2 Sonic vs Density
Neutron vs Density 38
38

CHAPTER 6
ASSESSMENT OF RESIRVOIR QUALITY IN CHAK7A-01
6.1 WELL RELATED PARAMETRS 41
6.2 Borehole lithology of CHAK7A-01 well 42
6.3 Selection of zone of interest in borehole log 43
6.4 Volume of Shale calculation 44
6.5 Saturation of Water in reservoir zone 45
6.6 Saturation of Hydrocarbons in reservoir zone 46

7.1
7.1
7.2
7.3
7.4
7.5 CHAPTER 7
CORELATION OF ALL WELLS
Volume of Shale in Reservoir Zone
Effective Porosity in Reservoir Zone
Water Saturation in Reservoir Zone
Hydrocarbon Saturation in Reservoir
Correlation of thickness of reservoir in the Wells
Overall correlation of CHAK63-01, CHAK66-01 and CHAK7A-01

47
47
48
48
48
50
CONCLUSIONS
REFERENCES 51
52

FIGURES
Figure 1.1
Figure 1.2
Figure 2.1
Figure 2.2
Figure 2.3
Figure 2.4
Figure 3.1
Figure 4.1
Figure 4.2
Figure 4.3
Figure 4.4
Figure 4.5
Figure 4.6
Figure 4.7
Figure 5.1
Figure 5.2
Figure 5.3
Figure 5.4
Figure 5.5
Figure 5.6
Figure 5.7
Figure 6.1
Figure 6.2
Figure 6.3
Figure 6.4
Figure 7.1

Figure 7.2
Location map of study area.
Base map of study area.
Regional tectonic setting of Pakistan.
Indus basin of Pakistan.
Structural setting of Sothern Indus basin Pakistan.
Stratigraphic sequence of Lower Indus basin.
Methodology adapted for Assessment of Reservoir Quality
Marking of Zone of Interest in CHAK63-01 well
Volume of Shale in reservoir of CHAK63-01well
Effective Porosity of Reservoir in CHAK63-01 well
Water Saturation in Reservoir zone of CHAK63-01 well
Hydrocarbons Saturation in Reservoir zone of CHAK63-01 well
Cross plot of Sonic vs Density (CHAK63-01 well)
Cross plot of Porosity vs Density (CHAK63-01 well)
Marking of Zone of Interest in CHAK66-01 well
Volume of Shale in reservoir of CHAK66-01well
Effective Porosity of Reservoir in CHAK66-01 well
Water Saturation in Reservoir zone of CHAK66-01 well
Hydrocarbons Saturation in Reservoir zone of CHAK66-01 well
Cross plot of Sonic vs Density (CHAK66-01 well)
Cross plot of Porosity vs Density (CHAK66-01 well)
Zone of interest in CHAK7A-01 well
Volume of Shale in Reservoir Zone of CHAK7A-01 Well
Saturation of Water in Reservoir Zone of CHAK7A-01 Well
Hydrocarbon Saturation in Reservoir Zone of CHAK7A-01 Well
Correlation of Basal Sand Zone in CHAK63-01, CHAK66-01 and CHAK7A-01.
Overall correlation of CHAK63-01, CHAK66-01 and CHAK7A-01 well 1
3
5
6
8
10
18
23
24
25
26
27
29
30
33
34
35
36
37
39
40
43
44
45
46
49

50

TABLES
Page
Table 4.1
Table 4.2 Well parameters of CHAK63-01
Borehole lithology of CHAK63-01 well 21
22
Table 5.1 Well parameters of CHAK66-01 31
Table 5.2 Borehole lithology of CHAK66-01 well 32
Table 6.1
Table 6.2
Table 7.1
Table 7.2
Table 7.3
Table 7.4 Well related parameters of CHAK7A-01 well
Bore Hole lithology of CHAK 7A-01 well
Correlation of Volume of Shale
Correlation of Effective Porosity
Correlation of Water Saturation
Correlation of Hydrocarbons Saturation. 41
42
47
47
48
48

?

CHAPTER 1
INTRODUCTION
Numerous techniques have been made and implemented in the past for estimation of reservoir quality. Petrophysical analysis using different well logs is the basis of these techniques. This thesis presents comprehensive overview on reservoir quality of studied area that have been assessed through well log interpretation.
1.1 Location
The study area is located near city of Tando Alam in Sanghar district, Sindh Province. OGDCL discovered the field in Sinjhoro Exploration Lease. In the Sanghar District Area allocated to the Sinjhoro Exploration Lease was 68o49’12″E – 69o9’0″E and 26o0’0″N – 26o15’0″N. The area lies in the Lower Indus Basin and covers the area of 1283.48 sq km which runs 55km east-west. Nearest cities are Jhakro and Shahdad-pur. Location of the study area on the map is shown in Figure 1.1.

Figure 1.1. Location map of study area (Pakistan Petroleum Information Services, 2010).

1.2 Exploration history of study area
In 1893 first well was in the Sindh by the Bombay Government. British Oil Company discovered first Gas well in 1957 at Khairpur District. In 1957 first giant Mari gas field was also discovered.
In 1961 Oil and Gas Development Corporation Limited (OGDCL) was established by Government of Pakistan to resuscitate exploration. After countless hard work, Sari gas field was discovered by OGDCL in 1966. Still, the focus of exploration remained in the Potwar area of Upper Indus Basin because Lower Indus Basin was considered to be only a gas prone area. Small number of efforts to explore the oil and gas were made in this region. From 1947-1980, the wells drilled in the Pakistan were 104 including 35 in Sindh. With the progresses in its technology OGDCL re-evaluated the potential prospects. However, exploratory drilling had not accelerated until 1981, when Union Texas Pakistan Inc discovered first oil field in the Lower Indus Basin, thus opposing the old perception that Sindh was only a gas prone region (Siddique and Baig, 2000).
After this success there was significant increase in the exploration activity throughout the Pakistan, mainly in Sindh. 198 wells were drilled in Pakistan from 1981-1994 out of which 144 were in Sindh. Till 1994 the total oil and gas fields discovered in the Pakistan were 100, 64 out of which are in Sindh Province. After the first discovery of oil made by PETRONAS in 1981 the OGDCL, the leading oil company of Pakistan is very active in petroleum exploration in Sindh province since. Till December, 1994 OGDCL has drilled 65 exploration wells and 38 development wells.23 Oil and Gas well were discovered out of 65 exploration wells. 13,500 Barrels per day are being produced from 10 oil fields of OGDCL’s at present day. For refining this crude oil is transported to Karachi. After the installion of four jet pumps at Tando Alam Complex the production share of Sindh’s Oil will increase at significant rate (Siddique and Baig, 2000).

1.3 Data acquired
For carrying out this study, well data has been utilized. Details of the data acquired are as follows:
From Landmark resources (LMKR) a total of 3 wells data were acquired with the prior approval of Directorate general petroleum concession (DGPC).
1.3.1 Wells
1) CHAK7A-01
2) CHAK63-01
3) CHAK66-01

1.4 Objectives
The main objective of the Petrophysical study of Gamma ray and Porosity is to transform the raw wireline log data into predictable rock properties such as fluid saturation, porosity and permeability.
The research is carried out with the following specific objectives.
• Water Saturation calculation
• Wells correlation using formation well tops
• Hydrocarbon Potential calculation

?
CHAPTER 2
REGIONAL GEOLOGIC FRAMEWORK
2.1 Tectonics
Northwestern boundary of Indian lithospheric plate is present in Pakistan. Due to the continuous subduction of Indian Plate beneath the Eurasian Plate from Eocene time, the tectonic features being shaped on the northern and northwestern borders of the Indian Plate are compressional thick-skinned in their nature.(Figure 2.1). “The continued under thrusting of the Indian Plate since Cretaceous produced the spectacular mountain ranges of the Himalaya and a chain of foreland fold-and-thrust belts as thick sheets of sediments thrusted over the Indian Craton (Dolan et al, 1987)”.
In Northern part of Pakistan, Himalayas are divided into four major sub-divisions. “Hindukush ranges and Karakoram lie in the north of the Main Karakoram Thrust (MKT). In the South of (MKT) and north of (MMT), Kohistan-Ladakh block is present (Dolan et al, 1987)”. Lower ranges of Kashmir, Swat and Hazara are parallel to the Lesser Himalayas of India and lie between the (MMT) Main Mantle Thrust and the (MBT) Main Boundary Thrust. The Potwar Plateau is bounded by the Salt Range Thrust (SRT) in south, representing the marginal foreland fold-and-thrust belt of Indian plate, equivalent to Sub-Himalayas of India (Ahmed, 1999).

2.2 Sedimentary basins of Pakistan
The area where sediments are preserved for the greater spans of time and described by the regional subsidence is called Basin. Sedimentary cover is the accumulation of sediments on the basement, which also called Basin Fill. Subsidence is the consistent settling of the basin and the point where maximum sediments accumulate is called the Depocenter. It may not resemble to the area of maximum subsidence (Pakistan Petroleum Information Services, 2010).
Pakistan has following Basins and these includes;
(1) Indus Basin
a. Upper Indus Basin.
b. Lower Indus Basin.
c. Central Indus Basin
d. Southern Indus Basin.
(2) Balochistan Basin.
a. Kakar Khorasan Basin (Pakistan Petroleum Information Services, 2010).

Figure 2.1. Regional tectonic setting of Pakistan (Pakistan Petroleum Information Services, 2010).

Figure 2.2. Indus basin, Pakistan (Pakistan Petroleum Information Services, 2010).

2.2.1 Southern Indus Basin
Regional structural style
The area covered by Southern Indus Basin starts from about 26o45′ N to the border of Pakistan and Indian coastline in the south. Kirthar Fold belt is bounding the Southern Indus Basin in the west and to the east it is bounded by the Nabisar slope. The Lower Indus Basin is oil and gas prone area with many oil and gas producing fields). In (Fig 2.3) Structural setting of Southern Indus Basin is shown.
a. Thar platform
Thar Platform is a monocline with gentle slope and analogous to Punjab Platform controlled by basement topography. In the east Indian shield is bounding the Thar platform, in the west it is merged into Karachi Trough and Kirthar and in North it is bounded by Mari Bhugti Inner Folded Zone (Hedley et al., 2001).
b. Karachi trough
It is an embayment which is opening up into the Arabian Sea. It has numerous anticlines which are forming narrow chains, while some of these anticlines contains gas fields, (Hundi, Sari, and Kothar). There are well preserved rocks of early, middle and late Cretaceous are present in this area. “Cretaceous/ Tertiary boundary where in Korara shales were deposited (Hedley et al., 2001)”.
c. Kirthar foredeep
Kirthar Foredeep is North-South trending, from the different wells correlation of Mari, Mazarani and Khairpur wells it seems that the Upper cretaceous age would be absent in the area. “Paleocene appears to be well developed in the depression, like Sulaiman depression, is the area of great potential for the maturation of source rocks (Hedley et al., 2001)”.
d. Kirthar foldbelt
North-south trending Kirthar Fold Belt is a tectonic feature that similar to sulaiman foldbelt. Rocks from Recent period to Triassic age were deposited in this area. The shape of the Kirthar foldbelt also indicates the closing of Oligocene-Miocene seas. “The western slice of the Kirthar foldbelt adjacent to the Baluchistan Basin, which marks the western edge of the Indus basin, is severely disturbed (Hedley et al., 2001)”.
e. Offshore indus
From cretaceous time sedimentation started, however the deltaic sedimentation and submarine sedimentation occurred science Oligocene time and offshore part of Indus Basin is passive continental margin (Hedley et al., 2001).

Figure 2.3. Structural Settings of Southern Indus Basin (Pakistan Petroleum Information Services, 2010).

2.3 Geology and tectonics of Sanghar/Sinjhoro block
The area of Sinjhoro exploration lease is the Thar Slope Platform. Indian Shield is bounding the study area in east while Karachi and Kirthar Trough in west and Mari-Bugti Inner Folded Zone in North. Indian plate started drifting toward North-East in Triassic period, during this period along the front edge of Indian plate in marginal sag basin sedimentation took place. While many sedimentary cycles can be recognized in this period. “There was no major tectonic activity until Cretaceous. First Orogeny started in Eocene which changed the whole geology of the area (Ahmed 1999).”
In the Oligocene period due to the full scale collision, second orogeny started and many areas were uplifted in East and South. In the rapidly subsiding narrow trough of Kirthar Area the marine sediments became restricted to it. “Towards the late Paleocene, the only elevations were the hills of folded beds and Indus Basin was filled with the sediments also Indus Basin must looks like a vast flood plain with braided stream(Ahmed, 1999)”.
2.4 Structural setting
Normal faults with Horst and Graben structures are results of extensional tectonics of the Southern Indus Basin with great importance in exploration of hydrocarbons. Offshore Indus Basin is sub-divided into Depression along a Hinge Line in close proximity and platform. “Offshore platform of Indus Basin is subdivided into Thar Platform and Karachi Trough by a line separating the Onshore Thar Slope from Karachi Trough. (Kemal, 1992)”.
2.5 Regional stratigraphy
The Sinjhoro block lies in the southern Indus Basin whose geology has been very well studied as well as mapped along with very well established stratigraphic units. The structures are exposed to the surface and can be defined on the aerial photographs.
The lithologies and stratigraphic succession were based on regional stratigraphic information and subsurface data. “Pliocene to Infra-Cambrian succession is mostly well known regionally (Kemal, 1992)”. Stratigraphy of Lower Indus Basin is illustrated in Figure 2.4.

Figure 2.4. Stratigraphic Sequence of Lower Indus Basin (Kemal, 1992).
2.6 Stratigraphy of study area
Stratigrapraphic succession of Lower Indus Basin is composed of the rocks of Siwaliks to the Sembar Formation. The Wells CHAK63-01, CHAK66-01 and CHAK7A-01 have been drilled to the depth of 3000m in the formations of Cretaceous, Paleocene, Eocene and Post Eocene ages. Between Alluvium and Laki formation an unconformity exists also between Parh Limestone and Khadro Formation an unconformity exists. “Stratigraphic sequence in the Lower Indus Basin remains more or less same as expected although slight variations in the thickness was observed (Kazmi, A.H. and Jan, M.Q., 1997)”.

2.7 Detailed stratigraphy of Formations of interest
(1) Lower Goru and Upper Goru Formation
The lower Cretaceous Lower Goru formation is most widely deposited in Sanghar area. Fine to coarse grained sandstone is major lithology with interstratified shale and intercalated siltstone. Mudstone, calcareous shale and marl are the main lithologies of Upper Goru Formation. “The color of Lower Goru and Upper Goru Formation varies from grey to black and at some places maroon. In the Eastern corner of Lower Indus Basin sand mostly sand is present (Kazmi, A.H. and Jan, M.Q., 1997)”.
(2) Parh Formation
Lime stone is main lithology of Parh Formation. Parh Formation is thin-to-medium-bedded and hard. The color of the formation varies from white to grey and at some places color is olive green and creamy. “Intercalations of marl and calcareous shale are also observed in the Parh Formation (Kazmi, A.H. and Jan, M.Q., 1997)”.
(3) Ranikot Fromation
The lithology of Ranikot formation is shale and medium to coarse grained, sub angular to sub rounded sandstone. The color of Ranikot formation ranges from white, light grey and translucent. “Shale is little bit calcareous and light to dark grey (Cheema et al., 1977)”.
(4) Sembar Formation
Sembar formation is composed of siltstone and brown/dark grey colored shale. “Greenish color in the rocks which is mostly due to the Galauconite is also observed in the Sembar Formation (Memon et al., 1999)”.
(5) Laki Formation
“Lithology of Laki formation is calcareous shale, chalk and grey to cream color limestone (Kazmi, A.H. and Jan, M.Q., 1997)”.

(6) Alluvium
The lithology of Alluvium is sandstone, shale, conglomerates and clay. Thickness of alluvium in the CHAK7A-01, CHAK63-01 and CHAK66-01 well ranges from the depths of 600m to 620m.
2.8 Petroleum geology of the study area
(1) Source rocks
Due to the organic richness the shale of lower Cretaceous Sembar formation is the proven source of hydrocarbons discovered in the Lower Indus Basin. Organic shale having good hydrocarbon potential is also present in the lower part of Lower Goru formation.
(2) Reservoir rocks
The zone of interest in the area is the Massive sands and Basal Sands of Lower Goru Formation. Basal Sand Zone is the main reservoir in the CHAK7A-01, CHAK63-01 and CHAK66-01 wells. Depth in these wells ranges from 2820 to 2860 m.
(3) Seal rocks
Thick sequence of shale and marl of the Upper Goru formation as well as shale within the Lower Goru serves as cap rock for the underlying sandstone reservoirs. The shale and marl sequence in the Upper Goru formation having a thickness of about 210m and was encountered at 1732m in well CHAK-63#01.

(4) Traps
Mostly the structural traps are present in the Sinjhoro area of Lower Indus Basin and usually these traps are related to normal faults. “Crotch traps and anticlinal traps usually referred as Classical traps are also found in this area. Below the Lower Goru unconformity some stratigraphic traps are also present (Ashraf et al., 1999)”.

(5) Migration pathways
Many faults are present in the Lower Indus Basin and these faults are the mean for the reservoir charge and hydrocarbons migration from the Sembar source rock. “These faults provide pathways for hydrocarbons from Sembar formation to Lower Goru Formation (Ahmed et al., 2004)”.

(6) Overburden rocks
“The Tertiary Laki, Kirthar and Ranikot formations are acting as overburden rocks (Ashraf et al., 1999)”.

CHAPTER 3
Methodology and Work Flow
The work flow and methodology described below is applied on data set to obtain required results. For this purpose Kingdom (8.4), Interactive Petrophysics(IP) and Microsoft Excel 2013 software were used.
Petrophysical characteristics of reservoir zone at Cretaceous level have been studied by using well log measurements. The geophysical well logs used for this study include natural gamma ray (SGR/ GR), sonic travel time (DT), latero log deep and shallow (LLD/LLS), density (RHOB), neutron-porosity (NPHI), caliper and spontaneous potential (SP). The well logs data along with formation tops, temperatures and mud filtrate resistivities of three wells entitled as Chak 63, Chak 66, Chak 73 from the Sinjhoro Gas field were obtained by Directorate General of Petroleum Concession (DGPC).
3.1 Wireline logs
Wireline logging also known as borehole logging, is to develop a detailed record of the geologic formations present in a borehole. The log may be based either on visual assessment of samples brought to the surface (geological logs) or on physical measurements made by lowering of instruments into the borehole (geophysical logs) (Tiabb, D. & Donaldson, E.C, 2004).
3.2 Well Logging objectives
The main purpose of well logging is:
(1) To provide data for assessing petroleum reservoirs.
(2) To aid in testing, completion and repairing of the well.
3.3 Types of well logging
Well logging is classified into three broad categories:
(1) Open Hole Logging
(2) Cased Hole Logging
(3) Production Logging

(1) Open hole logging
Logging surveys taken before the hole is cased are called open hole logs. Open hole logging include following logs:
(1) Electrical surveys (induction, laterolog and microlog logs)
(2) Sonic logs
(3) Radioactive surveys (neutron , density, and gamma ray logs)
(2) Cased hole logging
When the casing is lowered and after this the logging surveys that are taken are called Cased hole logs. The surveys included in this group are:
(1) Temperature
(2) Gamma Ray
(3) Neutron
(4) Pulsed Neutron
(5) Cement Bond Log
(6) Tracer Logs
3.4 Logs used for the study Of CHAK63-01, CHAK66-01 and CHAK7A-01
Following are the logs which were used for the assessment of reservoir quality from the CHAK63-01, CHAK66-01 and CHAK7A-01 wells.
(1) Gamma Ray Log
(2) Density (RHOB)
(3) Resistivity Log
(4) Neutron-porosity (NPHI)
(5) Sonic log
(1) Gamma Ray Log
The Gamma Ray log is usually run with most logging runs as a correlation tool since natural Gamma Rays can pass through casing. Production and perforating tools can be accurately positioned using the Gamma Ray as a correlation tool. Slim hole Gamma ray tool, 1 11/16″, 1 7/16″ and 1″ in diameter, can be run through tubing to correlate TCP (Tubing Conveyed Perforation) guns on depth. A Gamma Ray tool can be run in boreholes with up to 350degF, 20,000psi, and less than 24 inch hole diameter (Guéguen, Yves, Palciauskas and Victor, 1994).
(2) Resistivity Log
Resistivity logging is a method of well logging that works by characterizing the rocks and sediments in a borehole by measuring its electrical resistivity. Resistivity is a fundamental material property which characterizes how strongly material opposes the flow of electrical current. In resistivity logs, resistivity is measured using 4 electrical probes to eliminate the resistance of the contact leads. The log must run in holes containing electrically conductive mud or water. Resistivity logging is sometimes used in mineral exploration and water-well drilling, but most commonly for formation evaluation in oil- and gas-well drilling. Most rock materials are essentially insulators, while their enclosed fluids are conductors. If salty water is present in formation pores then overall resistivity will be low. If Hydrocarbons are present in the formation with the lower porosity of formation then the resistivity values will be higher. Hydrocarbons bearing formations contain usually high resistivities. If the mud used is water based and due to this oil is moved, deeper resistivity logs will display lower conductivity as compared to invaded zone. If mud used is oil based and water is moved, deeper logs will display higher conductivity as compared to invaded zone. This provides not only signs of the fluids present, as well as, at least quantitatively, whether the formation is permeable or not (Tiabb, D. ; Donaldson, E.C, 2004).
Types of resistivity logs includes
Various types of laterologs and induction logs are presently in the use, each
designed to decrease the opposing effects. These are given below.
a. Laterolog deep resistivity (LLD)
Laterologs release focusing currents to direct the track of the measured current from mud and invaded zone to the uninvaded area of formation.

b. Laterolog shallow resistivity (LLS) and microspherically focused log (MSFL)
The Dual Laterolog (DLL) contains two advanced laterolog tools, which share the similar electrodes on the primary Sonde
(3) Sonic Log
For formation interval transit time sonic log is used and it is a extent of a formation’s capability to convey seismic waves. Geologically, this capability differs with rock textures and lithology, most particularly decreasing with an increasing effective porosity. If the seismic velocity of the rock matrix, , and pore fluid, , are then a sonic log can be used to determine the porosity of a formation.
(4) Porosity Log
To calculate the total porosity of formation in the bore hole Density log is used, which displays the bulk density of the formation. These logs are used for recognition of accessory mineralogies, minerals in evaporate deposits, shale compaction, detection of gas, fracture recognition and complex lithologies, determination of oil-shale yield, determination of hydrocarbon density. Density logs are also called as porosity logs.
(5) Neutron Log
To identify the porous formations in bore hole and to calculate their porosity Neutron logs are used. Hydrogen is mostly present in Hydrocarbons and Neutron logs are response of hydrogen in the formation. Thus, in clean formations whose pores are saturated with oil or water, the neutron log shows the quantity of liquid filled porosity. Gas zones can often be recognized by comparing the neutron log with another porosity log. For more accurate values of porosity and lithology both these logs neutron and porosity are used.
3.5 Petrophysical interpretation
Petrophysics is the study of the physical properties that describe the occurrence and behavior of rocks, soils and fluids. Petrophysics mainly studies reservoirs of resources, including ore deposits and oil or natural gas reservoirs. Some of the key properties studied in Petrophysics are lithology, porosity, water saturation, permeability, density (Iqbal, B. Qadri., 1995).
3.6 Methodology adapted
Logs available for this study have been analyzed to measure the parameters by using different wireline logs. Following flow chart show all the parameters.

Figure 3.1. Methodology adapted for Assessment of Reservoir Quality.

i. Volume of Shale by Gamma Ray Log
In the quantitative evaluation of shale content, it is assumed that radioactive minerals other than shale are absent. The producing formation in well (Chak-63#01) is upper goru formation. Top of upper goru formation was at the depth of 1942m.
A gamma ray “shale index” IGR, has been defined as

Where,
GRlog = log response in the zone of interest, API units
GRmin = log response in the clean beds, API units
GRmax = log response in the shale beds, API units

ii. Porosity Calculation
Porosity Calculation Porosity of a formation is the volume of void spaces within the grains, which are capable of containment of fluid. Porosity can be of two kinds depending upon its depositional and degradational history. Primary porosity in a rock is a result of formation of pore spaces during the deposition of sediments and formation of a rock. Secondary porosity is a result of degenerative processes such as weathering or faulting, which create spaces in a rock for restraint of fluids.
iii. Density Porosity
The formula for calculation of density porosity is;
Where;
iv. Effective Porosity
Effective porosity of a formation can be defined as the sum of interconnected pore spaces. Effective porosity represents an area through which the fluid can flow in a rock. Effective porosity can be calculated by using the following formula;
Where;

v. Resistivity of Water
Resistivity of water is used to calculate the saturation of water. Rw is calculated by using SP values. In some cases where Self Potential does not develop Rwa method is used. Rwa is the resistivity of a mixture of chlorine and water in the pore spaces.Rw in water bearing rocks is equivalent to Rwa.
vi. Saturation of water
The fraction of pore spaces in a formation that contain water is termed as water saturation Sw. The remaining pore spaces in a formation hence contain 3690 3700 3710 3720 3730 3740 3750 3760 0 0.2 0.4 0.6 0.8 1 DEPTH m EFFECTIVE POROSITY v/v Depth Vs Effective Porosity Depth Vs Effective … 49 hydrocarbon. This is termed as hydrocarbon saturation Sh which is equal to 1-Sw. for calculation of Sw, Archie’s Equation is used which is as follows:

Where;

vii. Saturation of Hydrocarbon
Hydrocarbon saturation can be calculated by using the following formula:
Where;

CHAPTER 4
ASSESSMENT OF RESIRVOIR QUALITY IN CHAK63-01
For the assessment of reservoir quality of the Sinjhroo Field, Petrophysical analysis of different wells is done. The CHAK63-01 is an exploratory well located on the seismic line 2003-KH-44 on shot point 474 having the Latitude 25?51’33.34″ N and Longitude 68?43’01.51″ E. It is about 8 kilometer NNE of Naimat Basal 01 and 12.5 kilometer SSE of Siraj 01 well. It is located within the H-C fairway zone for Basal sand Unit. The well spudded on May 31, 2003 and reached to the total depth 3218 meter on July 21, 2003 in sand below Talhar shale, Good oil and gas shows were encountered in the reservoir section.
4.1 Well related parameters
Well related parameters are the values of different parameters used and calculated during drilling. The values of these parameters are given in following table.
CHAK63-01 WELL PARAMETERS
Loggers Depth 3055.3m
Bottom hole temperature 97.43 Deg.C
Mean surface temperature 18 Deg.C
Geothermal gradient 2.60 Deg.C/100m
Open hole size 21.00cm
Neutron log parameters Limestone porosity units
Maximum deviation from Bit size 7.50cm
Density correction limit 0.50gm/cc
Table 4.1 Well parameters of CHAK63-01

4.2 Borehole lithology of CHAK63-01 well
In CHAK63-01 well during drilling different lithologies were identified at different depths. These lithologies and their corresponding depths are given in following table Table (4.2).
Formations Depths in Borehole
Alluvium 000000.0
Laki 000618.0
Ranikot 001178.0
Khadro 001508.0
Parh 001579.0
Upper goru 001785.0
Lower goru 001942.0
Table 4.2 Borehole lithology of CHAK63-01 well
4.3 Selection of zone of interest
As borehole contains different formations, not all of them act as reservoir so we have to select zone of reservoir from different well log. One of the best well log for selection of zone of interest is Gamma ray log. With the aid of Gamma ray log clean and dirty lithologies can be differentiated.
In the Lower Indus Basin usually Lower Goru formation is acting as reservoir. Lower Goru formation contains Sand and Shale lithologies. Zone of Interest is selected from Gamma ray log. From the depths of 2830m to 2860m Gamma ray log shows low values as compared to above and below. This zone is identified as Basal Sand Zone which is acting as reservoir in the study area. Below this zone values of Gamma ray log are increasing due to presence of Talhar shale below this Basal sand zone (Fig 4.1).

Fig 4.1 Marking of Zone of Interest in CHAK63-01 well (SMT Kingdom suite 8.1)

4.4 Volume of Shale calculation
After the selection of zone of interest first step is to calculate volume of shale. Volume of shale is calculated by using formula explained earlier in methodology chapter (CHAPTER 3). Volume of shale is calculated on Microsoft excel and approximately 36% shale is present in the zone of interest. Volume of shale curve was generated in Kingdom suite 8.1. GR values for volume of shale are 45.02 for GR clean and 144.39 for GR shale. Volume of shale calculated in basal sand zone is less as compared to lithologies above and below.
Fig 4.2 Volume of Shale in reservoir of CHAK63-01well (SMT Kingdom suite 8.1)

4.5 Calculation of Effective Porosity in Reservoir Zone
Effective porosity is amount of interconnected pore space in the any area of interest. Amount of effective porosity is calculated with the help of Porosity log values and the log values of Volume of shale as explained earlier (CHALPTER 3). Total Porosity calculated in the reservoir zone is 16% while Effective Porosity is 10%. Both the percentages of Porosities are calculated with the help of Microsoft Excel Software. The value of the logs readings were taken from Interactive Petrophysics Software. The new log curve was generated (Fig 4.3) on Kingdom 8.1. From this log curve it is estimated that amount of effective porosity in reservoir zone is suitable for Hydrocarbons extraction.
Fig 4.3 Effective Porosity of Reservoir (SMT Kingdom suite 8.1)

4.6 Water Saturation in Reservoir Zone
For the Saturation of water in the pore spaces of the reservoir first Resistivity of water is calculated. SP log of the Well CHAK63-01 was used to find the Resistivity of water. After the resistivity of water Saturation of water is calculated. The log curve used for this purpose are LLD, Rw and Porosity logs. Values were taken from these logs and with methodology explained in previous section (CHAPTER 3), saturation of water is calculated on Microsoft Excel Software. The water saturation in the reservoir (Basal Sand Zone) is 73 %. The log curve (Fig 4.4) of water saturation with the depth is prepared on Kingdom Suit 8.1 Software.
Fig 4.4 Water Saturation in Reservoir zone (SMT Kingdom suite 8.1)
4.7 Hydrocarbon Saturation in Reservoir Zone
In the Basal sand stone (Reservoir Zone) all other calculation showed the indications of good reservoir characteristics. Hydrocarbons saturation is calculated on Microsoft Excel Software with the aid of methodology and formulas explained in last chapter (CHAPTER 3). In the Well CHAK63-01, Reservoir (Basal Sand Stone) has 27% Hydrocarbons Saturation. This Hydrocarbon Saturation with the depth is shown by curve (Fig 4.5) and this curve is prepared in Kingdom Suit 8.1 Software.
Fig 4.5 Hydrocarbons Saturation in Reservoir zone (SMT Kingdom suite 8.1)

4.8 Cross plots for identification of lithology
Different cross plots of various logs against each other are used for identification of lithology in Basal sand zone. Cross plots of different values of bulk density, sonic and neutron porosity are done against each other. These cross plots are done for the log values of Basal Sand Zone.
4.8.1 Sonic vs Density
The cross plot of the sonic verses density has been plotted on linear scale (Fig 4.6). It is to be noted that both of these logs have been displayed to the extents of the reservoir zone (between 2830 to 2860 meters). The color bar which distinguishes the small patches of GR values has also been displayed below. On plotting the cross plot, it can clearly be seen that output trend of the data points is linear and in decreasing order. Most of the data points are blue in color.
With the GR log on third axis we can distinguish between the sand and shale content in the reservoir zone. Blue color is showing that Sand is present in the reservoir along with the shale in the reservoir is also present.
4.8.2 Density vs Porosity
The cross plot of the porosity verses density has been plotted on linear scale (Fig 4.7). It is to be noted that both of these logs have been displayed to the extents of the reservoir zone (between 2830 to 2860 meters). The color bar which distinguishes the small patches of GR values has also been displayed below. On plotting the cross plot, it can clearly be seen that output trend of the data points is linear and in decreasing order. Most of the data points are blue in color.
With the GR log on third axis we can distinguish between the sand and shale content in the reservoir zone. Most of the GR values identified by color bar are present in between 15 to 20 and 120 to 125 showing that sand and shale both are dominant in the reservoir zone.

Fig 4.6 Cross plot of Sonic vs Density (CHAK63-01 well)
Fig 4.7Cross plot of Porosity vs Density (CHAK63-01 well)
CHAPTER 5
ASSESSMENT OF RESIRVOIR QUALITY IN CHAK66-01
CHAK66-01 well is exploratory well having latitudes “026.165194” and longitudes “068.876250” decimal degrees. Reservoir (Basal Sand Zone) is 15m thick and present at the depth of 2847m to 2862m in the well. Total depth of the well is 3050m and UWI of CHAK66-01 well is 001212. Different formations have been identified in this well.
5.1 WELL RELATED PARAMETRS
These different values are calculated during the drilling of the CHAK66-01 Well and showed in the following table (Table 5.1).
CHAK66-01 WELL PARAMETERS
Loggers Depth 3057.40
Bottom hole temperature 94.49 Deg.C
Mean surface temperature 18 Deg.C
Geothermal gradient 2.60 Deg.C/100m
Open hole size 21.00cm
Neutron log parameters Limestone porosity units
Maximum deviation from Bit size 7.50cm
Density correction limit 0.50gm/cc
Table 5.1 Well related parameters of CHAK66-01 well.
5.2 Borehole lithology of CHAK66-01 well
Different formations are present at different depths in borehole of the well. These formations with their corresponding depths are described in the following table (Table 5.2).

FORMATIONS DEPTH
ALLUVIUM 000000.0
LAKI 000612.0
RANIKOT 001161.0
PARH 001631.0
UPPER GORU 001773.0
LOWER GORU 002023.0
UPPER SAND-SHALE-MARL SEQUENCE 002023.0
BASAL SAND 002847.0
TALAR 002862.0
MASSIVE SANDS 002939.0
Table 5.2 Bore Hole lithology of CHAK 66-01 Well.

5.3 Selection of zone of interest in borehole log
From the analysis of previous well CHAK63-01 it is known that the reservoir zone in borehole is Basal Sand Zone. From the borehole lithology the depths of Basal Sand Zone are known but for further conformation GR log (Fig 5.1) is used for the selection of zone of interest.
In CHAK66-01 well the GR log trend is decreasing at the depth of 2847m, indicating the start of Basal Sand Zone. While in the Basal Sand Zone an increase in GR values can be observed which is the interbed of Shale at this zone. The end of Basal Sand Zone is marked at the depth of 2862m after that depth Talhar Shale is present.
Fig 5.1 Zone of interest in CHAK66-01 well
5.4 Volume of Shale calculation
Once the zone of interest is selected in the subsurface then Volume of Shale is calculated in the Basal Sand Zone. The values of GR Clean and GR Shale are 27.79 and 101.72 respectively. With the aid of methodology explained in previous sections (CHAPTER 3), volume of shale is calculated on Microsoft Excel Software. The log curve of Volume of Shale in Basal Sand Zone is generated on Kingdom 8.1 Software. Volume of Shale calculated is approximately 39% in the Basal Sand Zone of the Well CHAK66-01.
Fig 5.2 Volume of Shale in Reservoir Zone of CHAK66-01 Well

5.5 Effective porosity in the reservoir zone
The effective porosity of the reservoir zone is calculated with the methodology explained in CHAPTER 3. From the log curve of total porosity values are picked and then Effective Porosity is calculated on Microsoft Excel Software. After the calculation of Effective porosity log curve (Fig 5.3) is generated on Kingdom Suite 8.1. The log curve of Effective Porosity is showing that the Basal Sand Stone in CHAK66-01 well has high amount of interconnected pores which can be useful for the reservoir quality. Effective Porosity in CHAK66-01 well is approximately 11% with Total Porosity of 18.5%.
Fig 5.3 Effective Porosity of Reservoir Zone of CHAK66-01 Well

5.6 Saturation of Water in reservoir zone
Wire line log data is used for calculation of Water saturation in Basal Sand Zone. SP log is used for calculation of Resistivity of Water. After the resistivity of water Saturation of water is calculated. The log curve used for this purpose are LLD, Rw and Porosity logs. Values were taken from these logs and with methodology explained in previous section (CHAPTER 3), saturation of water is calculated on Microsoft Excel Software. The water saturation in the reservoir (Basal Sand Zone) is 76 %. The log curve (Fig 5.4) of water saturation with the depth is prepared on Kingdom Suit 8.1 Software.
Fig 5.4 Saturation of Water in Reservoir Zone of CHAK66-01 Well

5.7 Saturation of Hydrocarbons in reservoir zone
In the Basal sand stone (Reservoir Zone) all other calculation showed the indications of good reservoir characteristics. Hydrocarbons saturation is calculated on Microsoft Excel Software with the aid of methodology and formulas explained in last chapter (CHAPTER 3). In the Well CHAK63-01, Reservoir (Basal Sand Stone) has 24% Hydrocarbons Saturation. This Hydrocarbon Saturation with the depth is shown by curve (Fig 4.5) and this curve is prepared in Kingdom Suit 8.1 Software.
Fig 5.5 Hydrocarbon Saturation in Reservoir Zone of CHAK66-01 Well

5.8 Cross plots for identification of lithology
Different cross plots of various logs against each other are used for identification of lithology in Basal sand zone. Cross plots of different values of bulk density, sonic and neutron porosity are done against each other. These cross plots are done for the log values of Basal Sand Zone.
5.8.1 Sonic vs Density
The cross plot of the sonic verses density has been plotted on linear scale (Fig 5.6). It is to be noted that both of these logs have been displayed to the extents of the reservoir zone (between 2847 to 2862 meters). The color bar which distinguishes the small patches of SGR values has also been displayed below. On plotting the cross plot, it can clearly be seen that output trend of the data points is linear and in decreasing order. Most of the data points are blue in color.
With the SGR log on third axis we can distinguish between the sand and shale content in the reservoir zone. Blue color is showing that Sand is present in the reservoir along with the shale in the reservoir is also present.
5.8.2 Neutron vs Density
The cross plot of the neutron verses density has been plotted on linear scale (Fig 5.7). It is to be noted that both of these logs have been displayed to the extents of the reservoir zone (between 2847 to 2862 meters). The color bar which distinguishes the small patches of SGR values has also been displayed below. On plotting the cross plot, it can clearly be seen that output trend of the data points is linear and in decreasing order. Most of the data points are blue in color.
With the SGR log on third axis we can distinguish between the sand and shale content in the reservoir zone. Most of the SGR values identified by color bar are present in between 15 to 20 and 120 to 125 showing that sand and shale both are dominant in the reservoir zone.
Fig 5.6 Cross plot of Sonic vs Density (CHAK66-01 well)
Fig 5.7 Cross plot of Neutron vs Density (CHAK66-01)

CHAPTER 6
ASSESSMENT OF RESIRVOIR QUALITY IN CHAK7A-01
For the assessment of reservoir quality of the Sinjhroo Field, Petrophysical analysis of different wells is done. The CHAK7A-01 is an exploratory well located on the Latitude 026.184963 and Longitude 068.897333. It is located within the H-C fairway zone for Basal sand Unit. The well reached to the total depth 3050.00 meter in sand below Talhar shale, Good oil and gas shows were encountered in the reservoir section.
6.1 WELL RELATED PARAMETRS
These different values are calculated during the drilling of the CHAK7A-01 Well and showed in the following table (Table 6.1).
CHAK7A-01 WELL PARAMETERS
Loggers Depth 3050.00
Bottom hole temperature 95.47 Deg.C
Mean surface temperature 18 Deg.C
Geothermal gradient 2.60 Deg.C/100m
Open hole size 21.00cm
Neutron log parameters Limestone porosity units
Maximum deviation from Bit size 7.50cm
Density correction limit 0.50gm/cc
Table 6.1 Well related parameters of CHAK7A-01 well.
6.2 Borehole lithology of CHAK7A-01 well
Different formations are present at different depths in borehole of the well. These formations with their corresponding depths are described in the following table (Table 6.2).

FORMATIONS DEPTH
ALLUVIUM 0000.0
LAKI 0604.0
RANIKOT 1145.0
PARH 1642.0
UPPER GORU 1741.0
LOWER GORU 2102.0
UPPER SHALE 2102.0
BASAL SAND 2817.0
TALAR 2845.0
MASSIVE SANDS 2915.0
Table 6.2 Bore Hole lithology of CHAK 7A-01 well.
6.3 Selection of zone of interest in borehole log
From the analysis of previous well CHAK7A-01 it is known that the reservoir zone in borehole is Basal Sand Zone. From the borehole lithology the depths of Basal Sand Zone are known but for further conformation GR log (Fig 6.1) is used for the selection of zone of interest.
In CHAK7A-01 well the GR log trend is decreasing at the depth of 2817m, indicating the start of Basal Sand Zone. While in the Basal Sand Zone an increase in GR values can be observed which is the interbed of Shale at this zone. The end of Basal Sand Zone is marked at the depth of 2845m after that depth Talhar Shale is present.
Fig 6.1 Zone of interest in CHAK7A-01 well
6.4 Volume of Shale calculation
Once the zone of interest is selected in the subsurface then Volume of Shale is calculated in the Basal Sand Zone. The values of GR Clean and GR Shale are 37.86 and 141.22 respectively. With the aid of methodology explained in previous sections (CHAPTER 3), volume of shale is calculated on Microsoft Excel Software. The log curve of Volume of Shale in Basal Sand Zone is generated on Kingdom 8.1 Software. Volume of Shale calculated is approximately 30% in the Basal Sand Zone of the Well CHAK7A-01.
Fig 6.2 Volume of Shale in Reservoir Zone of CHAK7A-01 Well

6.5 Saturation of Water in reservoir zone
Wire line log data is used for calculation of Water saturation in Basal Sand Zone. SP log is used for calculation of Resistivity of Water. After the resistivity of water Saturation of water is calculated. The log curve used for this purpose are LLD, Rw and Porosity logs. Values were taken from these logs and with methodology explained in previous section (CHAPTER 3), saturation of water is calculated on Microsoft Excel Software. The water saturation in the reservoir (Basal Sand Zone) is 60 %. The log curve (Fig 5.4) of water saturation with the depth is prepared on Kingdom Suit 8.1 Software.
Fig 6.3 Saturation of Water in Reservoir Zone of CHAK7A-01 Well

6.6 Saturation of Hydrocarbons in reservoir zone
In the Basal sand stone (Reservoir Zone) all other calculation showed the indications of good reservoir characteristics. Hydrocarbons saturation is calculated on Microsoft Excel Software with the aid of methodology and formulas explained in last chapter (CHAPTER 3). In the Well CHAK7A-01, Reservoir (Basal Sand Stone) has 40% Hydrocarbons Saturation. This Hydrocarbon Saturation with the depth is shown by curve (Fig 4.5) and this curve is prepared in Kingdom Suit 8.1 Software.
Fig 6.4 Hydrocarbon Saturation in Reservoir Zone of CHAK7A-01 Well

CHAPTER 7
CORELATION OF ALL WELLS
In this chapter CHAK63-01, CHAK66-01 and CHAK7A-01 wells are correlated with each other. Volume of shale, Effective porosity, Water saturation and Hydrocarbon saturation of all the wells are correlated in order to find the quality of reservoir.
7.1 Volume of Shale in Reservoir Zone
Volume of shale in the reservoir of CHAK63-01, CHAK66-01 and CHAK7A-01 well shows that the reservoir contains the sand and shale interbeds. Analysis of the wells show that the volume of shale changed from 30 to 40% in reservoir along the interbeds of Sand. From the analysis it is confirmed that the lithologies in the basal sand zone are sand and shale.
CHAK63-01 CHAK66-01 CAHK7A-01
Volume of Shale 36% 39% 30%
Table 7.1 Correlation of Volume of Shale.
7.2 Effective Porosity in Reservoir Zone
Effective porosity of reservoir basal sand zone in the CHAK63-01, CHAK66-01 and CHAK7A-01 wells ranges from 10% to 20%. In CHAK63-01 well effective porosity is 16% while in CHAK66-01 well effective porosity is 10% showing that effective porosity is decreased in west of the reservoir but at the North of CHAK66-01 well effective porosity of CHAK7A-01 well is 20%.
CHAK63-01 CHAK66-01 CAHK7A-01
Effective Porosity 16% 11% 20%
Table 7.2 Correlation of Effective Porosity.

7.3 Water Saturation in Reservoir Zone
Water saturation in the reservoir ranges from 60% to 76%. In CHAK7A-01 well reservoir basal sand zone is least saturated with water as compared to CHAK63-01and CHAK66-01 wells. The values of saturation in the reservoir zone of above mentioned wells shows that the reservoir is of the good quality.
CHAK63-01 CHAK66-01 CAHK7A-01
Water Saturation 73% 76% 60%
Table 7.3 Correlation of Water Saturation.
7.4 Hydrocarbon Saturation in Reservoir Zone
Hydrocarbons saturation in Basal sand zone varies from 24% to 40 %. Hydrocarbon saturation in the CHAK66-01 well is 24% which is the lowest in the basal sand zone because effective porosity in the basal sand zone of CHAK66-01 well is also lowest of all the wells. Hydrocarbon saturation is highest at CHAK7A-01 well showing that the reservoir is at very good quality in this well.
CHAK63-01 CHAK66-01 CAHK7A-01
Hydrocarbons Saturation 27% 24% 40%
Table 7.4 Correlation of Hydrocarbons Saturation.
7.5 Correlation of thickness of reservoir in the Wells
Different lithologies are present at different depth in the wells. Thickness of reservoir basal sand zone in the well CHAK63-01 (Fig 7.1) is 30m at the depths of 2830m to 2860m in the well. In CHAK66-01 well thickness of basal sand zone is low as compared to the other wells. The thickness of basal sand zone at CHAK66-01 (Fig 7.1) is 15m at the depths of 2847m to 2852m.In CHAK7A-01 (Fig 7.1) well thickness of reservoir 28m at the depths of 2817m to 2845m. From the thickness of reservoir across the different wells in the area it can be suggested that the reservoir has good quality for the Hydrocarbons production along with other parameters like effective porosity, volume of shale and hydrocarbons saturation.

Fig 7.1 Correlation of Basal Sand Zone in CHAK63-01, CHAK66-01 and CHAK7A-01.
7.6 Overall correlation of CHAK63-01, CHAK66-01 and CHAK7A-01
Alluviam and Laki formation in all there wells has almost same thickness and these formation has no major importance for oil and gas. In CHAK7A-01 well Ranikot formation has less thickness as compared to the other two wells. While Khadro formation which is hard and tighy also very distinct from other formation as less thickness in CHAK7A-01(Fig 7.2) well as compare to others. Lower Goru formation in this area is subdivided into upper marl, sand and shale sequence and Basal sand zone which is also acting as reservoir. The Goru formation consist of interbed of shale, sandstone and marl. In the basal sand stone mostly shale is interbeded with sand and below basal sand stone Talhar shale is present.
Fig 7.2 Overall correlation of CHAK63-01, CHAK66-01 and CHAK7A-01 wells

CONCLUSION
For assessment of reservoir quality in the Sanghar field of lower Indus basin Pakistan, a comprehensive petrophysical analysis reservoir basal sand zone of lower Goru Formation was carried out in three wells. Different crossplots were generated for identification of lithology in basal sand zone, which shows that in the basal sand stone main lithologies are sandstone and shale. Shales are present in form of interbeds in the sandstone. By the petrophysical analysis of different wells it is cleared that Hydrocarbon saturation varies across these wells. Thickness of reservoir varies from 15m to 30m along these wells with Hydrocarbons saturation from 30% to 40%, which are good signs for commercial accumulation of Hydrocarbons.

REFERENCES
Ahmed, N., Fink, P., Sturrock, S., Mahmood, T. and Ibrahim, M., 2004. Sequence Stratigraph as Predictive Toold in Lower Goru Fairway, Lower and Middle Indus Platform, Pakistan, Annual Technicala Conference, 85-93.

Ahmed, S., 1999. Study on Oil and Gas Distribution in the Sinjhoro block: Union Texas Pakistan, Inc., SPE-PAPG, Annual Technical Conference, 137-147.

AI-Sadi, N.N., 1980, Seismic Exploration Technique and Processing, Birkhauser-Verlag, Boston, 259p.

Ashraf, E., Mahmood, S. and Ahsan, S.S., 1999. Reservoir Engineering Challenges in the Sanghar block, Pakistan, , SPE-PAPG, Annual Technical Conference, 297-309.

Bradley, M.E., 1985. Practical Seismic Interpretation, IHRDC Publishers, Boston, 266p.

Cheema, M.R., Raza, S.M., Ahmed, H. and Shah, S.M.I., 1977. Stratigraphy of Pakistan: Geologic Survey of Pakistan, Quetta, Memoirs 12, 56-98.

Dobrin, M.B. and Savit, C.H., 1988, Introduction to Geo-Physical Prospecting, McGraw-hill International edition, geology series. 867p.

Guéguen, Yves; Palciauskas, Victor (1994), Introduction to the Physics of Rocks, Princeton University.

Hedley, R., Warburton, J. and Smewing, J., 2001. Sequence Stratigraphy and Tectonics in Kirther Foldbelt, Pakistan. SPE Annual Technical Conference, 61-70.

Iqbal, B. Qadri., 1995. Petroleum geology of Pakistan, PPL Pakistan.

Kazmi, A.H. and Jan, M.Q., 1997, Geology and Tectonics of Pakistan, Graphic Publishers, Karachi, Pakistan. 560p.

Kemal, A., 1992. Geology and new trends of Petroleum Exploration in Pakistan. 16-57. In: Ahmed, G., Kernal, A., Zaman, A.S.H. and Humayon, M., 1991. Eds., New direction and strategies for accelerating petroleum exploration and production in Pakistan: Proceedings, International petroleum seminar, Ministry of petroleum and natural resources, Islamabad, Pakistan, November, 22-24.

Lillie, R.J., 1999, Whole Earth Geophysics: An Introductory Textbook for Geologists and Geophysicists , Englewood Cliffs, N.J., Prentice Hall, Inc., 361 pp.

Mavko, Gary; Mukerji, Tapan; Dvorkin, Jack (2003), The Rock Physics Handbook, Cambridge University.

Memon, A.D., Siddiqui, I. and Memon, A.A., 1999. The Role of Cretacious Rifts on the occurrence of Oil in Sindh Monocline, Pakistan, SPE-PAPG, Annual Technical Conference, 65-74.

Pennock, S. E., and Lillie, J.R., 1989. Structural interpretation of seismic reflection data from lower Indus basin, Pakistan. The American association of petroleum geologists bulletin, Y.73, No.7, 841-857p.

Siddiqui, Y.J. and Baig, M.I., 2000. Well completion experience in the Sinjhoro block, Pakistan: Union Texas Pakistan, Inc., SPE-PAPG, Annual Technical Conference, 283-294.

Tiabb, D. & Donaldson, E.C. (2004). Petrophysics. Oxford: Elsevier. p. 1.

Yilmaz, O., 2001. Seismic data analysis and processing, inversion and analysis of seismic data, Society of Exploration Geophysics, Tulsa. 2027p.

Post Author: admin

x

Hi!
I'm Eugene!

Would you like to get a custom essay? How about receiving a customized one?

Check it out