2d seismic interpretation and petrophysical analysis of kabirwala area, central indus basin ,...

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CHAPTER 1

INTRODUCTION

1.1 General Introduction

The study area which is licensed for exploration is Kabirwala located near

Khenawal, Central Indus basin in Punjab Province. The exploration license was

granted to Oil and Gas Development Company Limited (OGDCL). OGDCL spud

well to discover the prospective reserves in the region with few production wells.

1.2 Study Area

The area of the study is Kabirwala, which is located near Khenawal in the

Punjab region. The Kabirwala area lies in the Central Indus Basin which is bounded

by Sulaiman Depression on the east, Sargodha high on north and Sukkur rift in the

south. The well of the Tola reservoir area was first spud by the Oil and Gas

Development limited in 1974.

Figure 1.1. Location of the study area.

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1.3 Geological and Geophysical Data Used

The data for the research was obtained from the Land Mark Resources

(LMKR) as requested by Bahria University to Directorate General of Petroleum

Concessions Government of Pakistan (DGPC). Following of the data is acquired:

1.3.1 Seismic Lines:

Table: 1.1. Seismic lines provided for interpretation.

S.No Line Name Line Type Line Orentation

1. 854-KBR-49 Strike Line N-S

2. 854-KBR-50 Dip Line W-E



1.3.2 Well:

Table: 1.2. Well logs provided for the petro-physical analysis.

S.No Well Well Logs

1.

Tola-01

Gamma Ray Log

Bulk Density Log

Neutron Log

Sonic Log

Resistivity Log

1.4 Base Map

The base map shows the orientation of the seismic lines, shot points and the

well location on the seismic line. It shows the three of the strike lines and the other

one of the dip line in the opposite orientation. The dip lines KBR-50, KBR-51 and

KBR-52 have the shooting order starting from the West direction to the East direction

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whereas the stike line KBR-49 has the shooting order in the north to south direction as

mentioned in the above table 1.1. Below is the base map of the study area.

Figure.1.2. Base map of seismic lines of Kabirwala area.

1.5 Objectives of the Study

The main purposes of this discussion are as follows:

a) Make integrated interpretation of the available geophysical and geologic data.

b) Manipulate the acquired data into an image that can be used to infer the sub-

surface structure through time and depth contours.

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c) Identification of the structural trend of the area with the help of 3-D

visualization.

d) Identification of the prospect zones, if any and to analyze them by Petro

physical Analysis.

1.6 Methodology

The methodology involves the following steps:

a) To study the tectonic settings and geology of the area.

b) Preparation of base map for Tola 1974 seismic survey.

c) Marking the reflectors on the seismic sections.

d) Identifications of faults using the seismic sections.

e) Solving velocity windows for the calculation of depth.

f) Preparation of Time and Depth contour maps for the marked reflectors.

g) Interpretation of well logs of Tola-01.

h) Generation of graphs using the well log data.

i) To formulate most suitable recommendations and conclusions for the study

area.

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CHAPTER 2

REGIONAL GEOLOGY AND STRATIGRAPHY OF THE STUDY AREA

2.1 Introduction

As the area of research lies on the Indus basin. The Indus basin is further

divided into three basins as upper, central and lower. The Tola area is located and

affected by the tectonics of the central Indus basin. The central Indus basin is then

further divided into three zones as we move from the east to west. The further divided

zones are known as Punjab Platform, Sulaiman Depression and Sulaiman Fold belt. In

the northern side, the Middle Indus Basin is separated from the upper Indus Basin by

the Sargodha high and Pezu uplift (Kadri, 1997).

The southern boundary of the middle Indus basin is connected with the sukkur

rift, on the eastern side, the Indian shield plays its part and on the western side, the

Indian plate boundary marks the side of the central Indus basin.

As discussed earlier, the central Indus basin is divided into three zones known

as following zones (Kadri, 1995).

1. Punjab Platform

2. Sulaiman Foredeep

3. Sulaiman Fold belt

2.2 Punjab Platform

The Punjab platform is dedicated as the eastern side of the middle Indus basin

where the outcrops of the sedimentary rocks are not present (Kadri, 1995). The

Punjab platform is tectonically dipping beneath the Sulaiman Depression. As the

distance from the Indian Eurasian plate collision from the Punjab platform is very far,

therefore, the Punjab platform area is least affected by the tectonics of the Eocene age.

The number of folds and other structures are very less found as compared to the upper

of lower Indus basin.

There are many wells, which are drilled on this platform and based on the

drilling and the core analysis, the stratigraphic sequence and the sequence correlation

is generated. Moreover, the most significant pinch outs in Pakistan are revealed.

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Figure.2.1. Geologic map of Pakistan showing basins.

2.3 Sulaiman Foredeep

It is also known as the Sulaiman depression because of the presence of the

subsidence zone in this region. Along the southern rim of the Sulaiman Foredeep,

there is an arcuate and a transverse orientation of the stratigraphy. Because of the

collision, the depression is created in between and in this case, Sulaiman depression is

known to be that. The anticlines are proved by the seismic data evidence to be buries

and then transformed because of the flow of the Eocene shales (Kadri, 1995).

2.4 Sulaiman Fold belt

A large number of anticline features are generated in the result of the collision

of the Indian and Eurasian belt. All of these stratigraphic and geologic features are

very disturbed. There are a number of clearly detachments and huge anticlines in the

Sulaiman belt and Kirthar range along the eastern margins of the Sulaiman fold belt.

As we move towards the northern side, the eastern sides of the Sulaiman Fold belt has

the very huge but narrow anticlines, which are as long as tens of Kilometers having

the broken limbs which, are dipping towards the other side showing a reverse fault

with reverse dip separation. In addition, these special kinds of situation and the

tectonic activity generate the flower structure. The flower structure are the result of

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the wrench faulting of the large scale and generating the crude oil reservoirs like

Ranikot formation of the Paleocene age, Pab formation, Sember formation and the

Lower guru formation aged as Cretaceous. During the collision of the Eurasian plate

with the Indian plate, the basement rocks were categorized in three different zones.

These zones or blocks of the basement rocks are categorized and differentiated by

three different faults and also separates the central Indus basin. Out of these basement

rocks and the basement blocks, the Kirthar basement faults, which separate the

Sulaiman 18 from the Khuzdar, block. Similarly, the Jhelum basement fault separates

the Indo-Pakistan plate main body and the Hazara block. In addition, Sulaiman

basement fault separates the Hazara block and the Sulaiman block (Kadri, 1995).

2.5 Stratigraphy of Central Indus Basin

Figure2.2. Generalized stratigraphic column of the central Indus Basin (modified after Kadri, 1995).

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2.5.1 Miocene Age

2.5.1.1 Nagri Formation

Nagri Formation: It consists of sandstone with subordinate clay and

conglomerate. The upper contact with Dhok Pathan Formation is transitional. The age

is Late Miocene.

2.5.1.2 Chinji Formation

Chinji Formation: It consists of red clay with subordinate ash grey or brownish

grey sandstone. It is only confined to the southern half of the eastern Sulaiman Range

and is not developed in the rest of the Lower Indus Basin. In the Sulaiman Range it

disconformably overlies the Nari Formation. It is conformably overlain by Nagri

Formation. The age is Late Miocene.

2.5.2 Eocene Age

2.5.2.1 Ghazij Sui Member

Ghazij sui member predominantly consists of shales that act as a regional rock

in the area. The age is Eocene.

2.5.3 Paleocene Age

2.5.3.1 Dhungan Formaion

The term Dungan limestone was introduced by Oldham (1890). Williams

(1859) designated the type section to be near Harnai (lat. 300 08’ 38’’N; long. 670 59’

33’’E) and renamed the unit Dungan Formation. It consists of limestone, shale and

marl. The limestone is grey to buff, thin to medium bedded and conglomeratic. Shale

is grey, khaki and calcareous. The marl is brown to grey, thin to medium bedded and

fine grained. This formation is 50-400m maximum thick. Laterally this formational

facies is more diverse, at places thick limestone deposits while at places minor

limestone showings. The Sui main limestone is an upper part of Dungan limestone

due to its variable behavior. It is thick in the Zinda Pir, Duki, Sanjawi, Harand, and

also in Mughal Kot section but negligible as in Rakhi Gaj and Mekhtar areas.

Petroleum showings are common in this formation especially in the Khatan area

(Oldham 1890). Its lower contact with Bawata member of Rakhi Gaj Formation is

conformable, however near the Axial Belt it has disconformity at the base, while the

upper contact with Shaheed Ghat Formation is transitional and conformable. It has

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many mega forams. It age is considered as Late Paleocene, rarely exceeding to early

Eocene. However it is maintained all Paleocene in the Ziarat area and the Axial belt

areas where the Sangiali and Rakhi Gaj formations i.e. the lower and middle Sangiali

group is not developed. For example the Ziarat Laterite showing K-T boundary is

contacted by Parh and Dungan formation (Malkani, 2010).

2.5.3.2 Ranikot Formation

Ranikot formation is named after the Ranikot fortress in the Laki range near

Sind. The Ranikot group is also known to be as the infra Nummulitic. The Ranikot

group has been divided into three formation known as the lakhra (upper Ranikot),

Bara (lower Ranikot) and Khadro formation. The lower part has the sandstone of

brownish yellow color along with the shales and limestone. Similarly, the lower

Ranikot has the variegated sandstone and shale and the grey to brown color limestone

along with shale is present in the Lakhra formation.

2.5.4 Cretaceous Age

2.5.4.1 Lumshiwal Formation

The Lumshiwal formation is being exposed in the salt range as a type locality.

The Lumshiwal is covered across the Pakistan and has been named after the

Lumshiwal nala. There has been a variation in the lithologies and the thickness in this

formation all along. The Lumshiwal formation is being bedded as a thick one and the

color exposed is grey along with the bedding with the sandstone with the considerable

formations of sandy, glauconitic and silty shale towards the base. In the Lumshiwal

formation, the sandstone present is feldspathic and has a considerable amount of

carbon content. The age of the Lumshiwal formation in the area of the west side of

Kohat is Aptian and near Nizampur and southern part of Hazara, the age is upper

neocambrian to middle Albian.

2.5.4.2. Chichali Formation

As we know that in this area, Chichali formation is acting like a source rock

because of having shale in the formation. As the name implies, the Chichali is called

after the Chichali pass. The color of the formation is usually dark green to grayish

green and has sandy, silty and glauconitic shale in it. There are three members of the

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Chichali shales, which includes the lower member having the sandy shale with

phosphatic nodules. The in between member has the dark brown to green medium to

fine grain calcareous sandstone while the upper member joins the Chichali pass. The

contact of the Chichali formation with the Samana Suk formation lying beneath it is

disconfirmable, while the contact with the Lumshiwal is gradational.

2.5.5. Jurassic Age

2.5.5.1. Samana Suk Formation

Samana Suk formation has the limestone of the Jurassic age. It is the

formation of the Surghar group along with the Lumshiwal, Datta, Shinawari and

Chichali. The Samana Suk formation limestone has the very fine-grained limestone

along with the clay and sand. The formation reflects its environment of deposition as

the shallow marine or near coastal side. The lower contact of the Samana Suk

formation is with the Shinawari formation having the sand and a disconfirmable

contact with Chichali having shales mixed with sands.

2.5.5.2 Datta Formation

Datta formation comprises of sandstone, shales, siltstone and mudstone. Age

is Jurrasic. Datta shales act as good source rock whereas sandstones act as good

reservoir rock.

2.5.6 Triassic Age

2.5.6.1 Kingriali Formation

It consists of thin to thick bedded, massive, fine to coarse textured light grey

brown dolomite and dolomitic limestone with interbeds of shale and marl in the upper

part.The lower contact with Tredian Formation is transitional which is marked by

interbedding of sandstone and dolomite. The upper contact with the Datta Formation

is disconformable. The age is Late Triassic.

2.5.7 Permian Age

2.5.7.1 Amb Formation

This formation consists of sandstone, limestone and shale. The sandstone beds

occupy the lower part of formation. Upwards the sequence limestone with some shale

appears. The upper contact with Wargal Limestone is conformable.

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2.5.7.1 Warcha Formation

The formation consists of medium to coarse grained sandstone, conglomeratic

in places and interbeds of shale. The sandstone is cross bedded and arkosic. The

pebbles of the unit are mostly of granite of pink colour and of quartzite. It

conformably overlies the Dandot Formation. It is overlain by the Sardhai Formation

with the transitional contact. The age is Early Permian.

2.6 Borehole Stratigraphy

Table.2.1. Bore hole stratigraphy of Tola -01.

FORMATIONS FORMATION TOPS(m) THICKNESS

Nagri 0 484.00

Chinji 484 453.83

Nammal 937.82 40.20

Ghazij Sui Member 978.06 102.40

Dunghan 1080.46 36.86

Ranikot 1117.32 19.69

Lumshiwal 1132.00 30.63

Chichali 1167.63 6.42

Samana suk 1174.05 119.27

Shinawari 1293.32 106.68

Datta 1400.00 20.00

Kingriali 1420.00 84.14

Tredian 1504.14 66.86

Amb 1571.00 113.20

Sardhai 1684.20 125.80

Warcha 1810.00 19.00

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2.7 Petroleum system

A petroleum play is “Group of geologically related scenarios having similar

circumstances of source, reservoir and trap”(Kadri,1995). Within a basement, the

occurrence of the play elements plays a significant role in hydrocarbon accumulation.

The major petroleum play elements are:

a) Source rock

b) Reservoir rock

c) Seal rock

d) Trap

e) Migration

2.7.1 Source rock

The source rock in the Tola area is Datta Formation with major shale rock

present.

2.7.2 Reservoir rock

The reservoir rock is the Dhungan formation and Lower Ranikot formation of

Paleocene age and Samana Suk formation of Middle Jurassic age.

2.7.3 Seal rock

Ghazij Sui Member of Eocene age act as the seal rock for the Dhungan

formation.

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CHAPTER 3

SEISMIC DATA ACQUISITION AND PROCESSING

Seismic investigation starts in the field with the acquisition of seismic data.

Seismic survey is used in oil industry to get the picture of subsurface. In this method,

elastic properties of the subsurface materials are measured that vary with depth due to

change in lithology and pore fluids. The predominance of the Seismic method over

other geophysical method is due to various factors, the most important of which are

the high accuracy, high resolution and great penetration. Seismic surveys are of two

types i.e. seismic reflection and seismic refraction data.

A seismic source is a localized region within which the sudden bang produces

energy that leads to a rapid stressing of the surrounding medium. The typical seismic

source is an explosion. There is a wide variety of seismic sources, characterized by

differing energy levels and frequency characteristics.

Conversion of ground motion to an electrical signal requires a transducer. On

land, devices used for this purposes are known as seismometers or geophones and

hydrophones are used while surveying at sea.

3.1 Types of Seismic Methods

There are two types of seismic methods:

(a) Refraction Method.

(b) Reflection Method.

3.1.1 Seismic Refraction Method

The Seismic Refraction method is based on the study of the elastic waves

refracted along the geological layers in which the velocity of propagation of elastic

waves is greater than the overlying strata.

In order to have Seismic Refraction, the travelling wave must reflect critically

from the layers. The incident wave must strike at a critical angle on the interface

(where angle of refraction is 90 degrees). Then it travels along the boundary of the

interfaces and emerges where the angle ic = ir. In the figure we observe that the angle

of refraction is 90 degrees for one particular ray. It is the critically refracted ray that

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shows how the wave travels at speed V1 right along the top of the lower layer (After

Kearey, 1988).

3.1.2 Seismic Reflection Method

Seismic reflection data is used more frequently due to its wide application in

the oil industry. Reflection refers to the seismic energy that returns from an interface

of contrasting acoustic impedance, known as reflector. This energy is recorded at the

surface by sensitive detectors which respond to the ground motion produced by the

reflected energy in time from place to place, which is indicative of the shape of

structural features and their locations in sub-surface.

Therefore, reflection techniques are mainly used in oil industry to produce

structural maps of such deep-seated configurations such as anticlines, faults and salt

domes.

3.2 Seismic Data Acquisition

In simple terms and for all of the exploration environments, the general

principle is to send sound energy waves (using an energy source like dynamite or

Vibroseis) into the Earth, where the different layers within the Earth's crust reflect

back this energy. These reflected energy waves are recorded over a predetermined

time period (called the record length) by using hydrophones in water and geophones

on land.

The reflected signals are output onto a storage medium, which is usually

magnetic tape. The general principle is similar to recording voice data using a

microphone onto a tape recorder for a set period of time. Once the data is recorded

onto tape, it can then be processed using specialist software which will result in

processed seismic profiles being produced. These profiles or data sets can then be

interpreted for possible hydrocarbon reserves.

http://en.wikipedia.org/wiki/Vibroseis

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Figure 3.1. Basic layout of a seismic Data acquisition.

3.3 Acquisition surveying parameters

The acquisition surveying parameters are achieved through ‘hit and trial’

method; once the parameters are defined the survey is conducted. Acquisition

parameters used for given seismic data are:

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Table 3.1. General information about seismic lines under study (adopted from seismic section).

3.3.1 Source Parameters

During the seismic survey the data was recorded by using the following source

parameters.

Table 3.2. Source parameters for seismic lines under study (adopted from seismic sections).).

Energy Source Vibroseis (Vibrating in line)

Sweep Frequency 10-40Hz

Sweep Length 10 sec

Base of Vibroseis 120 meters

Y.P. Interval 100 meters

LINE NAME 854-KBR-49 854-KBR-50 844-KBR-51 844-KBR-52

Line Strike Dip Dip Dip

Line Direction South East East East

S.P 101-480 101-351 101-341 101-401

Data

Recorded February 1985 January 1985 December 1984 January 1985

Fold 24 24 24 24

Datum 150m

A.M.S.L

150m

A.M.S.L

150m

A.M.S.L

150m

A.M.S.L

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3.3.2 Recording Parameters

The parameters that are designed for seismic survey for acquiring high

resolution data. These parameters mainly depend upon the nature of survey,

topography of the area etc. These parameters are then stated with each recorded line

for further help in the processing of the line. Recording parameters used for this

survey are as follow:

Table 3.3. Recording parameters of the lines under study (adopted from seismic section).

Recorded By OGDCL

Instruments MDS-16

Tape Format SEG-C

Record length 16 sec

Notch filter Out

Sample interval 4 msec

Number of Data Traces 48

3.4 Seismic data processing

Once seismic data has been acquired on field, the second step is the processing

data. Processing is required to compensate for the imperfections of the seismic data

acquisition and degradation of the seismic waves during propagation. Seismic data

processing consists of applying a sequence of computer programs, each designed to

achieve one step along the path from field tape to record section. It involves the

enhancement of raw data to a form that is used for seismic interpretation. Data

processing converts the information recorded in the field into a form that mostly

facilitates geological interpretation (Al. Sadi, 1980).

Seismic data processing strategies and results are strongly affected by field

acquisition parameters. Additionally, surface conditions have a significant impact on

the quality of data collected in the field.

Seismic data processing strategies and results are strongly affected by the field

acquisition parameters. The purpose of seismic processing is to manipulate the

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acquired data into an image that can be used to infer the subsurface structure. Only

minimal processing would be required if we had a perfect acquisition system.

Seismic data processing involves a number of steps in enhancement of signal

to noise ratio (Yilmaz, 2001)

The sequence has been categorized as follows:

(a) Data Reduction.

(b) Geometric Corrections.

(c) Data Analysis and Parameter Optimization.

(d) Data Refinement.

(e) Data Presentation.

Figure: 3.2. Generalized processing flowchart.

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CHAPTER 4

SIESMIC INTERPRETATION

4.1 Introduction

Seismic interpretation includes several steps, which are taken to solve the

seismic section regarding all the stratigraphic, structural, and sequences. In the Oil

and Gas sector, the main purpose of the seismic analysis is to locate and observe the

best spot for the location of the hydrocarbon trapped in a certain structure, resisting its

flow. But in the case of the Kabirwala lines, the reflector are found to be basic

straight, thus cannot making any perfect trap for the hydrocarbon migration and

maturation.

4.2 Interpretation Steps

The seismic steps, which are performed to make a stratigraphic and structural

analysis in the Kabirwala seismic lines, are showed as following. The basic

interpretation steps are based on the seismic well log data of the Tola-01 in the

Kabirwala area and also by the four seismic lines and a base map which helps in

further analysis. Moreover, as the steps are completed, we are concluded with the

reflectors and its potential of producing, storing and stopping the flow of the

hydrocarbon migration. The steps are given below.

4.2.1 Velocity Window Solving

First of the step is to solve the velocity windows given on the top of the

seismic lines. As shown in the base map, the Tola-01 well lies on the seismic line

844-KBR-51. Therefore, the velocity windows are solved fot the KBR-51 seismic

section. On the velocity windows, one column is of the time in milliseconds and the

other column is of the RMS velocity. The RMS velocity is then multiplied with the

one-way travel time in milliseconds to give the depth by the formula S=VT. The one-

way travel time is acquired by dividing the time by 2. This column gives the depth of

each time during the recording of seismic waves travelling under the subsurface.

4.2.2 Time Depth Chart

As the velocity windows are solved, these are further plotted on a graph paper

with the depth on the horizontal axis against the time given in the velocity windows

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on the vertical axis. The depth chart is then plotted on the graph paper with all the

seven velocity windows.

Figure 4.1.Time depth graph of KBR-51

4.2.3 Reflector Marking

As shown before, the desired well is spud on the KBR-51 seismic line

therefore, the well tops of the Tola-01 well will be used in order to locate the required

reflectors on the seismic section. The well top data gives us the formation tops with

the required depth. The Kelly bushing is thus subtracted from the formation depth to

make the reflectors of the formations on a similar datum scale. As far as the well tops

of the Tola-01 are concerned, the tops of the required formation, which are Dunghan,

Samana Suk, Datta and Warcha are following:

Table 4.1.Formation tops of the marked reflectors.

Formation Depth(m)

Dunghan Formation 1080.46m

Samana Suk Formation 1174.05m

Datta Formation 1400.00m

Warcha Formation 1810.00m

0

2000

4000

6000

8000

10000

12000

14000

0 1000 2000 3000 4000 5000 6000

Time-Depth Graph

Time-Depth Graph

Time(msec)

Depth

(m)

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Therefore, the desired depths noted from the well tops of the Tola-01 are

located on the best-fit line curve created from the velocity windows calculations and

the graph helps to find the time against the depth on the seismic section.

On the time depth graph, the following are the time values of the required

depth using the depth time chart. As we know that the values of the time depth are

taken on the seismic line 845-KBR-43 therefore, the well is shown in the seismic line.

Moreover, a line is drawn from the required shot point across the seismic traces

towards the six second time vertically. And the values of the time are also located on

the well line over the seismic line. The time picked on the seismic line was as follows.

(1). Dunghan--------------------------------------1.24 sec

(2). Samana Suk ---------------------------------1.31 sec

(3). Datta------------------------------------------1.44 sec

(4). Warcha…………………………………1.55 sec

The traces on the specific time using the referred time scaling are therefore

used to locate the time on the well spot. In addition, after four traces are marked, four

of them are therefore spread using the common line joining the traces. The traces are

observed watching it parallel to the paper orientation rather looking it from top. The

horizons are marked on the seismic line.

4.2.4. Jump correlation

When all the seismic traces are marked on the seismic section of the 844-

KBR-51, the base map is then observed. On the base map, the orientation of the

seismic lines on a single paper is shown. In addition, the points of crossing of the lines

are shown very clearly. The base map of the Kabirwala seismic lines shows that the

seismic line KBR-51 at short point no 210 crosses the seismic line KBR-49 at short

point 350.

Therefore, KBR-51 is folded along the shot point 210 throughout the seismic

section and on the other hand seismic line KBR-49 is opened along and the folded

seismic line KBR-51 is held against the shot point no. 350 of KBR-49. The time lines

on the vertical axis are taken common and overlapped each other. The seismic traces

on the KBR-51 are continued on the line KBR-49 and are therefore marked

throughout the seismic section.

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As the seismic line KBR-51 is parallel to the KBR-50 and KBR-52 therefore,

jump correlation with each other is not possible and hence the seismic line KBR-49

which is the strike line is used to mark the horizons on KBR-50 and KBR-52.

Hence, the horizons are marked on the 854-KBR-50 using the seismic line

KBR-49 whose shot point no. 305 crosses the KBR-50 at the shot point no. 255. The

folded KBR-49 seismic line helps to mark Dunghan, Samana Suk, Datta and Warcha

on the KBR-50.

Similarly using KBR-49, the shot point no. 390 on it coincides with the shot

point no. 240 on the KBR-52. Therefore, by correlating, the seismic horizons are

marked on the KBR-52. Hence, four seismic lines are marked with the horizons.

Figure 4.2. Seismic sections marked horizons on 854-KBR 49

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Figure 4.3. Seismic sections marked horizons on 854-KBR-50

Figure 4.4. Seismic sections marked horizons on 844-KBR-51.

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Figure 4.5. Seismic sections marked horizons on 844-KBR-52.

4.2.5. Time picking

After the horizon marking on the seismic sections, the other task to do it to mark the time

on every shot point and the time is then noted down for every reflector as R1 for Dunghan, R2

for Samana Suk, R3 for Datta and R4 for Warcha. Moreover, the time is picked for each shot

point on each seismic line of Kabirwala. The trend of the reflectors is noted to be very straight

and linear; there is minor faulting or folded structure in the reflectors of Dunghan, Samana Suk,

Datta and Warcha. The four reflectors, thus has the approximately same time overall the seismic

section.

4.2.6. Time contour map

Contour map is generally defined as the line showing the same parameter (depth,

elevation) on a 2D map. Here, the contours are made with the help of the time values, which is

the time of the wave to reflect back from a prominent dense reflector or strata due to the acoustic

impedance contrast. For each reflector R1, R2, R3 and R4 the contours of the time are generated

on a map, taking the values of the reflector time picking on a line. In case of our research, the

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reflectors of our interest are the Dunghan, Samana Suk, Datta and Warcha and these are plotted

on the contour section referring to the reflection time values of these reflectors. Following are the

reflector contour maps of the 854-KBR-49, 854-KBR-50, 844-KBR-51 and 844-KBR-52.

As shown are the time contour maps of the four main reflectors of the four different

seismic sections on a single map. The reflection time is therefore plotted in order to give an idea

about the structure and the time delay of the seismic wave response due to the depth and other

deflecting measures in the path of the wave travel.

Figure 4.6. Time contour map of top of Dunghan Formation.

The time contour map of the Dunghan Formation shows a monocline structure dipping

towards the east direction. The seismic lines also conveys that there is minor faulting in these

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formations therefore, it implies that the Dunghan formation is gently dipping as a monocline

structure of the Punjab Platform. The time increases from 0.89 to 1.17 sec.

Figure 4.7. Time contour map of top of Samana Suk Formation.

The time contour map of the Samana Suk Formation also implies towards the monocline

structure dipping gently towards the east direction. The reflection time increases from 1.01 to

1.28 sec.

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The time contour map of the Datta Formation also give the picture of the monocline

structure as by the other two formations depicting the feature of the Punjab platform. The

reflection time increases from 1.06 sec to 1.4 sec.

Figure 4.8. Time contour map of Top of Datta Formation.

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Figue 4.9. Time contour map of top of Warcha Formation.

The time contour map of the Warcha Formation also implies towards the monocline

structure dipping gently towards the east direction. The reflection time increases from 1.24 to

1.56 sec.

4.2.7. Depth contour map

As shown in the following figures, the depth contour map is given which is generated

with the help of the reflection time values of the seismic lines of the Kabirwala area including

854-KBR-49, 854-KBR-50, 845-KBR-51, and 845-KBR-52. The depth contours shows the

structure of the area and gives the overall information about the depth and its range of the

particular formation. There are four reflectors on the seismic section of our concern and interest,

which are Dunghan Formation, Samana Suk Formation, Datta Formation and Warcha Formation.

Figure 4.9. Time contour map of top of Warcha Formation.

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As it can be seen in the figure that the reflectors were quite straight in the laterally and it is

therefore confirmed by the contour maps. These are marked as the reflector number 1, 2, 3 and 4

on the seismic section and the depth contour graph is according to these reflectors.

The depth contour maps show the same depth contour line for the single depth value. The

depth contour can help in giving the idea about the 3 dimensional structure of the particular

lithology showing its depth as a surface.

Figure 4.10. Depth contour map of top of Dunghan Formation.

In contrary to the time contour map, the depth contour map of the Dunghan formation

gives the same scenario about the dipping monocline structure of the Punjab Platform area of the

Figure 4.10. Depth contour map of top of Dunghan Formation.

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central Indus basin. The depth values of the Dunghan Formation is dipping towards Eastwards

and the depth values are decreasing from 1295 to 920 m.

Figure 4.11. Depth contour map of top of Samana Suk Formation.

The Depth contour map of the Samana Suk Formation shows the decreasing depth

northwards from 1480m to 1080m.

Figure 4.11. Depth contour map of top of Samana Suk Formation.

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Figure 4.12. Depth contour map of top of Datta Formation.

The depth contour map of the Datta Formation follows almost the same pattern as of the

Samana Suk Formation. The depth values are decreased from the 1610m to 1160m. The irregular

change in depth is noticed but the overall structure is a monocline structure of the Punjab

Platform.

Figure 4.12. Depth contour map of top of Datta Formation.

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Figure 4.13. Depth contour map of top of Warcha Formation.

The depth contour map of the Warcha Formation follows almost the same pattern as of

the Datta Formation. The depth values are decreased from the 1880m to 1400m northwards. The

irregular change in depth is noticed but the overall structure is a monocline structure of the

Punjab Platform.

4.2.8. 3D depth surfaces

The 3D depth surfaces are generated using the depth values by the help of Surfer

software. The 3D view of the specific formation surface helps in understanding the monocline

structure followed by in the Punjab Platform region towards northwards.

Figure 4.13. Depth contour map of top of Warcha Formation

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Depth

(m)

Figure 4.14. 3D depth surface of Dunghan Formation.

Figure 4.15. 3D Depth Surface of Samana Suk Formation

Depth

(m)

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Depth

(m)

Figure 4.16. 3D depth surface of the Datta Formation.

Figure 4.17. 3D depth surface of the Warcha Formation.

Depth

(m)

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CHAPTER 5

PETROPHYSICAL ANALYSIS & INTERPRETATION OF WELL LOGS

5.1 Well Log Analysis

5.1.1 Purpose of the study

The objective and purpose of our petro-physical analysis is to determine different rock

properties that exists within the zone of interest in reservoir horizons in order to depict pay zones

present in reservoir horizons and to quantify the hydrocarbon saturation present in it via log

techniques in Tola-1 well. The following steps are followed to achieve this objective.

(a) Carrying out log interpretation to mark the suitable reservoir zones (pay zones).

(b) Computation of reservoir rock characteristics using various wire line logs.

(c) Interpretation of the measured parameters for the evaluation of the hydrocarbon potential

of the study area.

Figure 5.1. Complete Log interpretation work flow

5.2 Methodology

The general methodology implemented for petro-physical analysis is given below:

(a) Firstly, the formation tops of understudy reservoir horizons got marked on logs at their

respective depths.

Log Readings

Marking of Reservoir zones

Lithology Identification

Calculation of Shale volume

Calculation of Density porosity &

Effective porosity

Calculation of Water Resistivity

Evaluation of Water Saturation (Sw)

Evaluation of Hydrocarbon Saturation (Sh)

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(b) Than zone of interest got marked based on marking of crossover between Neutron and

density curves.

(c) Gamma ray log is used in the identification of lithology.

(d) Porosity measurements using Neutron log.

(e) Bulk density measurements using density log.

(f) Gamma ray log interpretation for the calculation of Shale volume and Effective

porosity.

(g) Calculation of Permeability and Bulk volume of water by using saturation of water and

effective porosity

(h) Analysis of Resistivity logs for calculation of formation water resistivity and hence for

the calculation of Saturation of Water and Saturation of Hydrocarbons.

5.3 Raw Log Data

The raw log data was obtained from LMKR. The data contained the raw log

curves. Following logs got obtained.

(a) Gamma Ray Log

(b) Neutron Log

(c) Density log

(d) Resistivity Log

5.3.1 Gamma Ray Log

A common and inexpensive measurement of the natural emission of gamma rays by a

formation. Gamma ray logs are particularly helpful because shales and sandstones typically have

different gamma ray signatures that can be correlated readily between wells. A log of the total

natural radioactivity, measured in API units. The measurement can be made in both open hole

and through casing. The depth of investigation is a few inches, so that the log normally measures

the flushed zone. Shales and clays are responsible for most natural radioactivity, so the gamma

ray log often is a good indicator of such rocks, giving high values of gamma rays, while shale

free sand stones have low values of gamma ray, because of less concentration of radioactive

materials in them. However, other rocks are also radioactive, notably some carbonates and

feldspar-rich rocks.

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5.3.2 Neutron Log

Referring to a log of porosity based on the effect of the formation on fast neutrons

emitted by a source. Hydrogen has by far the biggest effect in slowing down and capturing

neutrons. Since hydrogen is found mainly in the pore fluids, the neutron porosity log responds

principally to porosity. However, the matrix and the type of fluid also have an effect. The log is

calibrated to read the correct porosity assuming that the pores are filled with fresh water and for

a given matrix (limestone, sandstone or dolomite).

5.3.3 Density Log

Density logging is a well logging tool that can provide a continuous record of a

formation's bulk density along the length of a borehole. In geology, bulk density is a function of

the density of the minerals forming a rock (i.e. matrix) and the fluid enclosed in the pore spaces.

This is one of three well logging tools that are commonly used to calculate porosity.

The density log measures the electron density of the formation via the backscatter of

gamma rays, which is related to true bulk density. The neutron log attempts a measurement of

formation porosity by using the interaction between neutrons emitted through tool and hydrogen

within the formation (Neutron-Density suite).

5.3.4 Resistivity Suite

A log of the resistivity of the formation, expressed in ohm-m. The resistivity can take a

wide range of values, and, therefore, for convenience is usually presented on a logarithmic scale

from, for example, 0.2 to 2000 ohm-m. The resistivity log is fundamental in formation evaluation

because hydrocarbons do not conduct electricity while all formation waters do. Therefore a large

difference exists between the resistivity of rocks filled with hydrocarbons and those filled with

formation water. Clay minerals and a few other minerals, such as pyrite, also conduct electricity,

and reduce the difference.

5.4 Zone of Interest

First of all, we used Gamma Ray Log to mark the clean zones and then the log trends of

Neutron and Density logs were identified at clean zones. Crossovers were found between

Neutron and Density log curves. These crossovers were the indication of hydrocarbons in the

selected zone. The presence of hydrocarbons was also confirmed by the resistivity curves. Hence

we marked one zone of interest.

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Table 5.1 Zones of interest.

Zone Formation Formation top (ft) Formation bottom (ft) Total Thickness (ft)

Zone 1 SAMANA SUK 3855 4240 385

Zone 2 DATTA 4595 4655 60

5.5 Lithological Identification

Gamma Ray log is used to determine the lithology. According to them the lithologies

were sandstones and shales majorly.

5.6 Determination of volume of shale (Vsh)

Volume of shale was calculated with the help of GR log. First of all the maximum

and minimum values of the GR curve are determined and then the GR readings at different

intervals are taken in each zone marked. Then, with the help of this data, shale volume or

gamma ray shale index (IGR) is determined at different depth intervals with the help of the

following formula Volume of shale was calculated by using Gamma Ray log. The values of the

log depicted that radioactive materials were not present in the clear zone which indicated that

shale was not present in the clear zone. (Schlumberger, 1974):

IGR =𝐆𝐑𝐋𝐨𝐠−𝐆𝐑𝐌𝐢𝐧.

𝐆𝐑𝐌𝐚𝐱.−𝐆𝐑𝐌𝐢𝐧.

Where,

GRlog = Log response in the zone of interest, API units

GRmin = Log response in the clean beds of minimum gamma ray deflection, in API

units

GRmax = Log response in the shale beds of maximum gamma ray deflection, in API

units

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5.7 Total porosity

Porosity is defined as the number of void spaces as compared to the total volume of rock.

These spaces are formed in the rock either during its deposition which is called primary porosity

or due to the dissolution of grains by water or fracturing in which case it is called secondary

porosity. It is denoted by “ϕ” and is expressed in percentage. Porosity can be determined through

different ways but we determined porosity through two ways (Schlumberger, 1974)

Total or Average Porosity = (Density porosity + Neutron porosity) /2

5.8 Neutron porosity

Referring to a log of porosity based on the effect of the formation on fast neutrons

emitted by a source. Hydrogen has by far the biggest effect in slowing and capturing neutrons.

Since hydrogen is found in pore fluids, the neutron porosity log responds principally to porosity.

Neutron Porosity= Readings from Neutron log.

5.9 Density porosity

If the density log is used alone porosity can be determined by using ;

𝝋D = 𝝆𝐦 − 𝝆𝐛

𝝆𝐦−𝝆𝐟

𝜌m= matrix density (g/cm3) constant 2.71

𝜌b= log reading (g/cm3)

𝜌f = density of mud filtrate (g/cm3) constant 1

Inaccuracies may occur when taking readings in evaporites or gas bearing

formations. The lower density will predict porosity higher than the actual value.

5.10 Effective porosity

Effective porosity is the sum of all interconnected pore spaces. Effective Porosity

is determined by using following formula:

Effective porosity = Total porosity * (1-Vsh)

Where, Vsh= Volume of shale

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5.11 Resistivity of water (Rw)

Resistivity of water is the resistivity of an unknown mixture of water and chlorine in the

pore spaces. It is the most sensitive parameter in the computation of water saturation. The

resistivity of water is calculated by using several techniques.

5.12 Water saturation

The amount of water present in the pore spaces is called saturation of water and is

denoted by “Sw”. Water saturation is calculated with the help of Archie’s (1942) equation.

(Sw)n = √(

𝓪

𝛗𝓶) × (Rw

Rt)

Where,

Sw= Saturation of Water

= Effective Porosity

𝓂=2 Cementation exponent

a= 1 (Tortuosity factor)

n= 2 (Saturation exponent)

Rw= Formation water resistivity

Rt= Formation true resistivity

5.13 Hydrocarbon saturation

The amount of oil or other hydrocarbons present in the pore spaces is called the

hydrocarbon saturation and is denoted by “Sh”. The determination of saturation of hydrocarbon

is very important because it will depict the reservoir potential to produce hydrocarbons. If the

saturation of hydrocarbon is very high then the next step begins but if the saturation of

hydrocarbon is very small or less then well is considered to be dry because less saturated

reservoir will not compensate for the drilling expenditures of the company. Hydrocarbon

saturation is determined by the following formula (Schlumberger, 1974):

SH=1-Sw

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Where,

SH= Saturation of Hydrocarbon

Sw= Saturation of Water

5.14 Bulk volume of water

Bulk volume of water is calculated with formula:

BVW = Sw× φE

Where,

BVW = Bulk volume of water

φE = Effective porosity

Sw = Water Saturation

5.15 Permeability

Permeability is determined by using following formula (Schlumberger, 1977):

𝑲𝒆=[𝟐𝟓𝟎⨉(𝝋𝟑 𝑺𝒘⁄ )]𝟐

Where,

𝐾𝑒= Permeability

𝜑= Effective porosity

𝑆𝑤= Saturation of Water

5.16 Petrophysical Analysis of Reservoir Zones

5.16.1 Samana Suk Formation - Zone # 1

In the figure 5.2, volume of shale mostly varies from 40 to 80%. This percentage of

volume of shale depicts that the lithology is partially clean and partially dirty and represents

some presence of sandstone in Sandstone formation.

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Figure 5.2. Correlation between depth and volume of shale in Samana Suk formation.

In the figure 5.3, effective porosity varies between 3 to 15 % upto a depth of 4772m and

then decreases till 4773m which shows that after 4772m, compaction starts which damages the

interconnectivity of pores.

3800

3850

3900

3950

4000

4050

4100

4150

4200

4250

4300

0 20 40 60 80 100

Volume of Shale in %

Zone 1Dep

th (

ft)

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Figure 5.3 . Correlation between depth and effective porosity in Samana Suk formation.

In the figure 5.4, the saturation of water continously changes with the depth and this

variation is due to the fractures or compaction present in the formation.

3800

3850

3900

3950

4000

4050

4100

4150

4200

4250

4300

0 10 20 30 40 50 60

Zone 1

Dep

th (

ft)

Effective Porosity in %

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Figure 5.4 . Correlation between depth and saturation of water in Samana Suk formation.

By comparing the figures 5.4 and 5.5, we can clearly identify that these two graphs are

inverted images of each other. This represents that with an increase in saturation of hydrocarbon,

the saturation of water decreases and vice versa.

3800

3850

3900

3950

4000

4050

4100

4150

4200

4250

4300

65 70 75 80 85

Zone 1Dep

th (

ft)

Saturation of Water

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3800

3850

3900

3950

4000

4050

4100

4150

4200

4250

4300

0 10 20 30 40

Zone 1

Dep

th (

ft)

Saturation of Hydrocarbon

Figure 5.5 . Correlation between depth and saturation of hydrocarbon in Samana Suk formation.

5.16.2 Datta Formation - Zone # 2

In the figure 5.6, volume of shale mostly varies between 0-85% which shows that

lithology of the formation is partially clean and partially dirty and therefore indicates a reservoir

zone.

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4590

4600

4610

4620

4630

4640

4650

4660

0 20 40 60 80 100 120

Zone 2

Dep

th (

ft)

Volume of Shale in %

Figure 5.6 . Correlation between depth and volume of shale in Datta Formation.

In the figure 5.7 the effective porosity is almost minimum at all depths and ranges from 5-25%.

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4590

4600

4610

4620

4630

4640

4650

4660

0 5 10 15 20 25 30

Zone 2

Effective Porosity in %

Dep

th (

Fee

ts)

Figure 5.7. Correlation between depth and effective porosity in Datta Formation.

In the figure 5.8, the saturation of water almost lies between the range of 0-10%. This

shows that this zone is less water saturated and more hydrocarbon saturated.

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Figure 5.8. Correlation between depth and saturation of water in Datta Formation.

By comparing the figures 5.8 and 5.9, we can clearly identify that these two graphs are

inverted images of each other. this represents that with an increase in saturation of hydrocarbon,

the saturation of water decreases and vice versa.

4590

4600

4610

4620

4630

4640

4650

4660

88 89 90 91 92 93

Zone 2

Dep

th (

ft)

Saturation of Water

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4590

4600

4610

4620

4630

4640

4650

4660

0 2 4 6 8 10 12

Zone 2

Dep

th (

Fee

ts)

Saturation of Hydrocarbon

Figure 5.9 , Correlation between depth and saturation of hydrocarbon in Datta formation.

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5.17 RESULTS

Table 5.2. Average properties of Reservoir zones of Samana Suk and Datta formation

Zones Volume of

Shale (%)

Effectively

Porosity

Saturation of

Water

Saturation of

Hydrocarbon

Zone 1 41.17% 18.14% 76.43% 23.67%

Zone 2 56% 13.90% 90.96% 9.1%

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CONCLUSIONS

• The seismic data interpretation of the area delineate the presence of horst and graben

structure in the research area.

• The time sections confirms the formations are getting shallower in west direction and

deeper in the east direction.

• The mapping shows the structure is dipping in the east west direction.

• The mapping of the fault boundaries shows they are dipping in the east and west

direction.

• The 3D structural analysis shows the whole structure is getting shallower in the west

direction and deeper in the east direction.

• On the basis of petrophysical analysis zone 1 has better hydrocarbon potential than zone

2

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REFERENCES

Kazmi, A.H., and Jan, M.Q., 1997. Geology and tectonic of Pakistan, Graphic publishers,

Karachi, Pakistan.

Yilmaz., 2001. Seismic data analysis and processing, Inversion and analysis of seismic

data, Society of exploration geophysics, Tulsa.

Coffen, J.A., 1984. Seismic Exploration Fundamental, Pennwell Publishing

Company, Tulsa, Oklahoma, 74101.

Dobrin, M.B. and Savit, C.H., 1988. Introduction to Geophysical Prospecting,

McGrawhillinternation edition, geology series.

Asquith, G., and D. Krygowski, 2004, Basic Well Log Analysis: AAPG Methods in

Exploration 16, p.31-35

Gakkhar, R.A., (2012), “Source-rock Potential and Origin of Hydrocarbons in the

Cretaceous and Jurassic Sediments of the Punjab Platform (Indus Basin) Pakistan”, Search and

Discovery Article # 50572

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