GEOLOGICAL MAPPING AND OIL RESERVE ESTIMATION

IN MEHSANA OIL FIELDSTATE OF GUJARAT, INDIA.

Report on the Project work submittedin partial fulfilment for the requirement

of the Degree of

Master of Technologyby

SUBU.SUDEESABABUReg. No. 56040001

SCHOOL OF MARINE SCIENCESCOCHIN UNIVERSITY OF SCIENCE AND

TECHNOLOGYCOCHIN - 682016

JUNE 2006

INTRODUCTION

Oil and natural gas are an important source

of Energy. It is an important source from

which organic material, plastics, life-saving

medications, clothing, cosmetics, pesticides,

and many other items you may use daily.

The petroleum geologist is the center pier in

the foundation of the petroleum industry. The

industry is completely dependent upon a

continuing discovery of new pools, or

extension of old pools, for maintenance of its

supply crude oil and thereby of itself; and

most certainly “the discovery and production

of oil is a geologic enterprise.”

About ONGC- Institute of Reservoir Studies The Institute of Reservoir Studies (IRS) was

founded in 1978 as a single- source and multi-

service reservoir engineering agency with the

objectives to:

• Maximize hydrocarbon recovery at minimum cost• Provide holistic reservoir description through integration of all data• Maximize the value of proven reserves with conventional and improved recovery techniques• Enhance the skills and knowledge for better reservoir management

Fig: ONGC-Institute of Reservoir Studies, Ahmedabad

This project here at IRS was about sub-surface

Geological Mapping and Estimation of reserves OIIP

(Oil Initial Inplace). The study area is located within

the Cambay Basin near the Mehsana town, State of

Gujarat, India. The structure in this area was

delineated in early sixties. The earlier well drilled in

the study area did not yield encouraging results but

latter wells drilled proved to be hydrocarbon

bearing. The well encountered about 11m of oil

column in sandstone reservoir of Kalol Formation.

The study area mainly comprises of sandstones,

shales, and claystones with shales generally

forming the non-reservoir part of the oil field. Most

of these Formations belong to Middle-Eocene, age.

At the very beginning of the training program, I

introduced to the basic concepts of Petroleum

Geology, Logging and Enhanced Oil Recovery

Techniques. Following that we were given a

basic demonstration of the software used in log

correlation. As part of the introduction that can

be summarized-as-follows.

Our study was confined only to the peak an

individual of the sand unit which we refer to as

sand unit-1. Various parameters like porosity, oil

saturation etc. were determined in this area

through various logs taken from One Hundred

and Thirty-six (136 Nos.) wells drilled in the

study area which were then used for

determining various aspects-of-the-field.

OBJECTIVE OF THE STUDY

Although the study area had good permeability,

but due to high viscosity of the oil the primary

recovery was quite low. In order to enhance the

recovery of the field a Geocellular model was

prepared and various Enhance Oil Recovery

schemes were carried out one of them being In-

Situ Combustion method. This study was

basically to determine, volumetric reserves of

hydrocarbon in the sand unit-1 of the study

area.

GENERAL GEOLOGY OF THE STUDY AREA

The study area lies in the northern part of

Ahmedabad-Mehsana tectonic block of Cambay

Basin. The Cambay basin is a N-S trending intra-

cratonic rift bounded on eastern and western

margins by N-S Boundary faults. Major transfer

faults divide the basin into eight tectonic blocks

and Mehsana is one of them. The Deccan Traps

forms the technical basement in the basin and is

overlained by thick pile of Tertiary sediments.

FIG: Study Area ( Ahmedabad Mehsana Block)

Stratigraphy of Cambay Basin

GEOLOGICAL MAPPING & OIL RESERVE

ESTIMATIONS Subsurface mapping is practiced chiefly in working

out the geology of petroleum deposits .The

information from well data, however, makes geologic

mapping in three dimensions possible over wide

areas in which there are no outcrops and whose

underground geology could not be deciphered by the

earlier methods. Geologic maps of many kinds are

prepared from these data to show various conditions

underground, and these maps are interpreted to

show the geologic history of the region and to predict

the location of petroleum pools yet undiscovered.

Subsurface structure may be mapped on any

formation boundary, unconformity, or producing

formation that can be identified and correlated by

well data. Structure may be shown by contour

elevation maps or by cross-sections. Since most

formations in the oil regions are below sea level, the

contoured elevations are generally minus figures,

meaning bellow sea level datum, and subsurface

structural maps are sometimes called sub-sea maps.

PROCEDURE

The process early involves log correlation which is

done using a software known as LANDMARK. This data

is then used for preparation of base maps which are

produced using LANDMARK which itself has a subsidy

known as Z-Map plus which is used for obtaining base

maps. Various contour maps are prepared on this

base maps from which latter volumetric estimation

are done.

CORRELATION The sand unit of the study area is about 10m - 11m

broad with horizons bearing shale. Sandstones are

coarse to fine grained, grey colored, medium to well

sorted and at places limonitic.

The unit-1 can also be subdivided locally into sub-units

on the basis of the development of intervening shale

layers. However development of these shale layers are

very localized and are restricted mostly along the

crestal part of the structure, hence making sand unit-1

as a single hydro dynamic unit. The unit-1 also shows

development of thin layers of coal / carbonaceous

streaks in some part of the field.

RESERVOIR PARAMETERS

The provided data which include the reservoir

parameters like NPHI (Neutron Porosity), RHOB (Bulk

Density), CALI (Caliper Logging), GR (Gamma ray

Logging), ILM (Medium Resistivity), VCL (Volume of

Clay type Material relative to total volume), SP

(Spontaneous Potential), DT (Distance Travel, Sonic),

RT (True Resistivity)

Using the following equations we can find out the

various reservoir parameters such as water

saturation (Sw), oil saturation (So), porosity (Phi)

have been computed at log sampling rate for entire

study area and are used for preparing Geocellular

model and volumetric estimation. Average layer

wise parameters have been computed and the

values can be listed in underneath table.

I. VCLRT (Volume of Clay calculated from True Resistivity):

VCLRT = Rclay X RLim – RT

RT RLim – Rclay

Rclay = 2.5

RLim = 1000

2. VCLGR (Volume of Clay calculated from Gamma Ray Log):

VCLGR = GR – GR min

– GR max GR min

3. VCLmin (Volume of Clay Minimum): VCLmin = Min (VCLRT, VCLGR) 4. PHIS (Porosity Calculated from Sonic Log):

PHIS = Δt - Δtma + Vclay (Δtma – Δtclay)

Δtf - Δtma Δtf - Δtma

Δt = DT, Δtma = 55.5 (sst), Δtf = 189, Δtf – Δtma = 133.5

Vclay = Volume of Clay minimum

Δtclay = DT. max value

5. PHID (Porosity calculated from Density Log):

PHID = (RHOB – RHOma) + Vclay (RHOma – RHOclay)

(RHOf – RHOma) (RHOf – RHOma)

RHOB = Bulk Density

RHOf = Average Fluid Density

RHOclay = High GR corresponding RHO value

Vclay min = Volume of Clay minimum

RHOf = 1.0, RHOma = 2.65

6. PHINC (Neutron Porosity Corrected):

PHINC = PHIN – (Vclay min X PHIN Clay)

PHIN = Neutron Porosity

Vclay min = Volume of Clay minimum

PHIN Clay = 0.54

7. PHIE (Effective Porosity):

PHIE = (7 X PHID) + (2 X PHINC)

9

PHID = Porosity calculated from Density Log

PHINC = Neutron Porosity corrected.

8. SW (Water Saturation):

SW = 1/SW -1

SW-1

= [(Vcl

(1-Vcl) ) + (

m/2 ) ] x RT

SW = Saturation of Water

Vcl = Volume of Clay minimum

Rclay = High VCL minimum corresponding RT value

a = 0.62

m = 2.15

RW = 0.25

= Effective Porosity

RT = True Resistivity

a X Rw

2 Rclay

9. SO (Oil Saturation):

SO = (1 – SW)

SW = Water Saturation

10. F (Formation Resistivity Factor)

F = a / m

m = Cementation Factor

a = Constant, 0.81 for sand, 1.0 for compact formation

= Effective Porosity

11. RW (Resistivity of Saturated Formation):

RW = RT / F

RT = True Resistivity

F = Formation Resistivity Factor

AVERAGE RESERVOIR PARAMETERS OF SAND UNIT-1

Well No TOP BOT

KB (mt)

TOP msl

BOT msl

Gross thic

Net thic hp PHI

wat sat Sw

OIL sat So Hp*So*Phi IHM

2 922.00 932.51 61.99 860.01 870.52 10.51 3.38 0.25 0.58 0.42 0.3549 0.355 4 916.97 927.82 61.90 855.07 865.92 10.85 3.13 0.16 0.54 0.46 0.230368 0.230 5 931.61 944.23 62.38 869.23 881.85 12.62 7.00 0.26 0.53 0.47 0.8554 0.855 6 923.20 934.29 60.71 862.49 873.58 11.09 3.05 0.26 0.53 0.47 0.37271 0.373 7 914.20 924.24 60.67 853.53 863.57 10.04 4.88 0.24 0.50 0.50 0.5856 0.586 8 920.50 930.03 62.04 858.46 867.99 9.53 3.00 0.28 0.58 0.42 0.3528 0.353 9 918.90 929.70 61.87 857.03 867.83 10.80 6.86 0.23 0.57 0.43 0.678454 0.678

10 917.87 928.49 61.27 856.60 867.22 10.62 4.60 0.19 0.55 0.45 0.3933 0.393 11 947.23 955.55 63.59 883.64 891.96 8.32 0.00 0 0.000 12 927.43 936.14 61.76 865.67 874.38 8.71 3.96 0.26 0.58 0.42 0.432432 0.432 13 939.60 947.72 63.06 876.54 884.66 8.12 2.90 0.30 0.51 0.49 0.4263 0.426 14 926.38 935.79 60.38 866.00 875.41 9.41 4.59 0.23 0.50 0.50 0.52785 0.528 16 937.84 951.74 61.38 876.46 890.36 13.90 7.93 0.27 0.41 0.59 1.263249 1.263 18 928.73 938.63 61.00 867.73 877.63 9.90 7.61 0.29 0.45 0.55 1.213795 1.214 19 920.90 928.64 61.91 858.99 866.73 7.74 5.13 0.26 0.47 0.53 0.706914 0.707 20 955.03 963.17 63.01 892.02 900.16 8.14 0.00 0 0.000 23 939.12 948.65 62.12 877.00 886.53 9.53 0.38 0.31 0.78 0.22 0.025916 0.026 24 942.71 952.29 60.70 882.01 891.59 9.58 0.00 0 0.000 25 926.90 937.36 52.02 874.88 885.34 10.46 5.21 0.20 0.54 0.46 0.47932 0.479 27 922.86 932.41 61.10 861.76 871.31 9.55 2.44 0.20 0.55 0.45 0.2196 0.220 28 915.80 925.85 60.39 855.41 865.46 10.05 4.23 0.24 0.44 0.56 0.568512 0.569 29 993.02 1005.02 138.02 855.00 867.00 12.00 5.05 0.21 0.44 0.56 0.59388 0.594 30 985.54 993.61 123.54 862.00 870.07 8.07 4.42 0.23 0.59 0.41 0.416806 0.417 31 923.44 934.53 61.28 862.16 873.25 11.09 4.66 0.23 0.50 0.50 0.5359 0.536 33 920.23 927.25 61.93 858.30 865.32 7.02 2.56 0.23 0.52 0.48 0.282624 0.283 34 924.18 931.54 62.34 861.84 869.20 7.36 0.00 0.00 0.00 1.00 0 0.000 35 934.50 947.90 61.93 872.57 885.97 13.40 5.64 0.21 0.54 0.46 0.544824 0.545 36 958.14 967.70 105.14 853.00 862.00 9.00 5.21 0.21 0.66 0.34 0.371994 0.372 37 920.50 930.47 62.35 858.15 868.12 9.97 6.79 0.21 0.55 0.45 0.641655 0.642 38 923.44 931.28 62.51 860.93 868.77 7.84 2.44 0.26 0.62 0.38 0.241072 0.241 39 982.78 992.58 132.01 850.77 860.57 9.80 6.79 0.22 0.59 0.41 0.612458 0.612 42 920.45 931.54 60.02 860.43 871.52 11.09 8.84 0.26 0.44 0.56 1.287104 1.287 43 916.63 924.58 62.13 854.50 862.45 7.95 1.52 0.19 0.67 0.33 0.095304 0.095 44 1005.03 1016.37 147.03 858.00 869.34 11.34 6.10 0.19 0.58 0.42 0.48678 0.487 45 977.48 986.70 129.51 847.97 857.19 9.22 7.93 0.25 0.64 0.36 0.7137 0.714 46 923.92 935.58 60.26 863.66 875.32 11.66 6.87 0.22 0.56 0.44 0.665016 0.665 48 919.32 931.61 60.18 859.14 871.43 12.29 6.62 0.23 0.48 0.52 0.791752 0.792 49 937.84 946.09 62.33 875.51 883.76 8.25 4.63 0.26 0.68 0.32 0.385216 0.385 50 928.74 937.96 60.30 868.44 877.66 9.22 4.72 0.28 0.44 0.56 0.740096 0.740 52 981.05 992.12 127.13 853.92 864.99 11.07 6.73 0.23 0.45 0.55 0.851345 0.851 53 920.50 931.80 61.06 859.44 870.74 11.30 2.13 0.22 0.46 0.54 0.253044 0.253 54 922.17 931.85 59.99 862.18 871.86 9.68 5.18 0.23 0.42 0.58 0.691012 0.691 55 919.34 929.72 61.80 857.54 867.92 10.38 3.18 0.29 0.46 0.54 0.497988 0.498 56 981.86 993.74 127.80 854.06 865.94 11.88 10.52 0.32 0.31 0.69 2.322816 2.323 57 921.64 930.86 61.13 860.51 869.73 9.22 2.90 0.18 0.61 0.39 0.20358 0.204

Well No TOP BOT

KB (mt)

TOP msl

BOT msl

Gross thic

Net thic hp PHI

wat sat Sw

OIL sat So Hp*So*Phi IHM

60 943.20 954.97 62.00 881.20 892.97 11.77 0.00 61 994.55 1004.78 129.80 864.75 874.98 10.23 4.07 0.28 0.72 0.28 0.319088 0.319 62 978.86 990.16 124.06 854.80 866.10 11.30 8.01 0.21 0.44 0.56 0.941976 0.942 64 976.56 985.88 127.83 848.73 858.05 9.32 5.18 0.25 0.46 0.54 0.6993 0.699 65 921.48 929.94 62.36 859.12 867.58 8.46 7.49 0.29 0.33 0.67 1.455307 1.455 66 917.02 928.48 61.70 855.32 866.78 11.46 6.69 0.27 0.51 0.49 0.885087 0.885 70 914.79 925.04 62.12 852.67 862.92 10.25 4.03 0.22 0.48 0.52 0.461032 0.461 71 923.30 933.00 62.58 860.72 870.42 9.70 5.12 0.24 0.52 0.48 0.589824 0.590 72 920.60 927.97 62.69 857.91 865.28 7.37 1.98 0.31 0.54 0.46 0.282348 0.282 73 927.51 938.99 62.96 864.55 876.03 11.48 6.48 0.30 0.52 0.48 0.93312 0.933 74 926.38 936.65 61.61 864.77 875.04 10.27 1.22 0.25 0.49 0.51 0.15555 0.156 75 924.63 933.70 60.21 864.42 873.49 9.07 5.18 0.22 0.45 0.55 0.62678 0.627 76 932.43 940.17 59.60 872.83 880.57 7.74 4.92 0.26 0.53 0.47 0.601224 0.601 77 927.00 937.71 62.00 865.00 875.71 10.71 4.64 0.27 0.44 0.56 0.701568 0.702 78 917.08 925.93 60.08 857.00 865.85 8.85 6.10 0.23 0.52 0.48 0.67344 0.673 79 927.58 935.14 59.88 867.70 875.26 7.56 6.41 0.30 0.29 0.71 1.36533 1.365 80 917.48 926.70 61.12 856.36 865.58 9.22 2.59 0.26 0.40 0.60 0.40404 0.404 81 940.70 950.86 59.68 881.02 891.18 10.16 4.72 0.29 0.60 0.40 0.54752 0.548 83 918.45 930.92 62.46 855.99 868.46 12.47 8.22 0.24 0.44 0.56 1.104768 1.105 84 931.30 940.47 61.54 869.76 878.93 9.17 3.75 0.26 0.42 0.58 0.5655 0.566 85 929.14 947.65 60.63 868.51 887.02 18.51 7.47 0.26 0.30 0.70 1.35954 1.360 86 922.95 937.83 60.45 862.50 877.38 14.88 6.71 0.33 0.45 0.55 1.217865 1.218 87 932.65 938.70 63.20 869.45 875.50 6.05 4.42 0.30 0.45 0.55 0.7293 0.729 91 939.66 950.33 61.34 878.32 888.99 10.67 4.75 0.32 0.57 0.43 0.6536 0.654 92 923.91 934.80 60.07 863.84 874.73 10.89 0.88 0.25 0.45 0.55 0.121 0.121 93 924.92 935.10 59.63 865.29 875.47 10.18 9.54 0.33 0.33 0.67 2.109294 2.109 94 929.42 936.86 62.30 867.12 874.56 7.44 4.38 0.28 0.47 0.53 0.649992 0.650 96 923.12 931.93 60.38 862.74 871.55 8.81 3.50 0.32 0.59 0.41 0.4592 0.459 97 929.14 937.79 63.05 866.09 874.74 8.65 7.03 0.31 0.51 0.49 1.067857 1.068 98 927.95 938.23 61.48 866.47 876.75 10.28 4.71 0.24 0.53 0.47 0.531288 0.531 99 920.49 931.51 60.00 860.49 871.51 11.02 8.57 0.30 0.42 0.58 1.49118 1.491

100 926.73 935.72 61.45 865.28 874.27 8.99 5.00 0.28 0.72 0.28 0.392 0.392 102 931.00 939.47 63.50 867.50 875.97 8.47 5.38 0.32 0.54 0.46 0.791936 0.792 103 915.55 923.35 61.56 853.99 861.79 7.80 3.64 0.25 0.50 0.50 0.455 0.455 104 934.12 950.35 63.75 870.37 886.60 16.23 5.33 0.25 0.46 0.54 0.71955 0.720 105 933.16 1003.75 61.16 872.00 880.00 8.00 4.24 0.22 0.47 0.53 0.494384 0.494 107 930.42 940.72 62.70 867.72 878.02 10.30 4.45 0.27 0.42 0.58 0.69687 0.697 108 933.98 946.21 60.13 873.85 886.08 12.23 1.50 0.39 0.62 0.38 0.2223 0.222 109 926.94 933.64 63.20 863.74 870.44 6.70 3.83 0.29 0.48 0.52 0.577564 0.578 111 926.98 933.92 61.74 865.24 872.18 6.94 2.88 0.15 0.61 0.39 0.16848 0.168 114 926.85 932.83 62.09 864.76 870.74 5.98 3.13 0.24 0.52 0.48 0.360576 0.361 115 922.99 931.91 61.49 861.50 870.42 8.92 4.88 0.23 0.48 0.52 0.583648 0.584 116 927.98 931.93 62.83 865.15 869.10 3.95 7.57 0.28 0.48 0.52 1.102192 1.102 117 921.04 929.37 61.55 859.49 867.82 8.33 3.38 0.21 0.62 0.38 0.269724 0.270 118 926.31 934.63 62.34 863.97 872.29 8.32 3.31 0.27 0.38 0.62 0.554094 0.554 119 928.56 939.56 61.00 867.56 878.56 11.00 6.00 0.32 0.60 0.40 0.768 0.768

Well No TOP BOT

KB (mt)

TOP msl

BOT msl

Gross thic

Net thic hp PHI

wat sat Sw

OIL sat So Hp*So*Phi IHM

60 943.20 954.97 62.00 881.20 892.97 11.77 0.00 61 994.55 1004.78 129.80 864.75 874.98 10.23 4.07 0.28 0.72 0.28 0.319088 0.319 62 978.86 990.16 124.06 854.80 866.10 11.30 8.01 0.21 0.44 0.56 0.941976 0.942 64 976.56 985.88 127.83 848.73 858.05 9.32 5.18 0.25 0.46 0.54 0.6993 0.699 65 921.48 929.94 62.36 859.12 867.58 8.46 7.49 0.29 0.33 0.67 1.455307 1.455 66 917.02 928.48 61.70 855.32 866.78 11.46 6.69 0.27 0.51 0.49 0.885087 0.885 70 914.79 925.04 62.12 852.67 862.92 10.25 4.03 0.22 0.48 0.52 0.461032 0.461 71 923.30 933.00 62.58 860.72 870.42 9.70 5.12 0.24 0.52 0.48 0.589824 0.590 72 920.60 927.97 62.69 857.91 865.28 7.37 1.98 0.31 0.54 0.46 0.282348 0.282 73 927.51 938.99 62.96 864.55 876.03 11.48 6.48 0.30 0.52 0.48 0.93312 0.933 74 926.38 936.65 61.61 864.77 875.04 10.27 1.22 0.25 0.49 0.51 0.15555 0.156 75 924.63 933.70 60.21 864.42 873.49 9.07 5.18 0.22 0.45 0.55 0.62678 0.627 76 932.43 940.17 59.60 872.83 880.57 7.74 4.92 0.26 0.53 0.47 0.601224 0.601 77 927.00 937.71 62.00 865.00 875.71 10.71 4.64 0.27 0.44 0.56 0.701568 0.702 78 917.08 925.93 60.08 857.00 865.85 8.85 6.10 0.23 0.52 0.48 0.67344 0.673 79 927.58 935.14 59.88 867.70 875.26 7.56 6.41 0.30 0.29 0.71 1.36533 1.365 80 917.48 926.70 61.12 856.36 865.58 9.22 2.59 0.26 0.40 0.60 0.40404 0.404 81 940.70 950.86 59.68 881.02 891.18 10.16 4.72 0.29 0.60 0.40 0.54752 0.548 83 918.45 930.92 62.46 855.99 868.46 12.47 8.22 0.24 0.44 0.56 1.104768 1.105 84 931.30 940.47 61.54 869.76 878.93 9.17 3.75 0.26 0.42 0.58 0.5655 0.566 85 929.14 947.65 60.63 868.51 887.02 18.51 7.47 0.26 0.30 0.70 1.35954 1.360 86 922.95 937.83 60.45 862.50 877.38 14.88 6.71 0.33 0.45 0.55 1.217865 1.218 87 932.65 938.70 63.20 869.45 875.50 6.05 4.42 0.30 0.45 0.55 0.7293 0.729 91 939.66 950.33 61.34 878.32 888.99 10.67 4.75 0.32 0.57 0.43 0.6536 0.654 92 923.91 934.80 60.07 863.84 874.73 10.89 0.88 0.25 0.45 0.55 0.121 0.121 93 924.92 935.10 59.63 865.29 875.47 10.18 9.54 0.33 0.33 0.67 2.109294 2.109 94 929.42 936.86 62.30 867.12 874.56 7.44 4.38 0.28 0.47 0.53 0.649992 0.650 96 923.12 931.93 60.38 862.74 871.55 8.81 3.50 0.32 0.59 0.41 0.4592 0.459 97 929.14 937.79 63.05 866.09 874.74 8.65 7.03 0.31 0.51 0.49 1.067857 1.068 98 927.95 938.23 61.48 866.47 876.75 10.28 4.71 0.24 0.53 0.47 0.531288 0.531 99 920.49 931.51 60.00 860.49 871.51 11.02 8.57 0.30 0.42 0.58 1.49118 1.491

100 926.73 935.72 61.45 865.28 874.27 8.99 5.00 0.28 0.72 0.28 0.392 0.392 102 931.00 939.47 63.50 867.50 875.97 8.47 5.38 0.32 0.54 0.46 0.791936 0.792 103 915.55 923.35 61.56 853.99 861.79 7.80 3.64 0.25 0.50 0.50 0.455 0.455 104 934.12 950.35 63.75 870.37 886.60 16.23 5.33 0.25 0.46 0.54 0.71955 0.720 105 933.16 1003.75 61.16 872.00 880.00 8.00 4.24 0.22 0.47 0.53 0.494384 0.494 107 930.42 940.72 62.70 867.72 878.02 10.30 4.45 0.27 0.42 0.58 0.69687 0.697 108 933.98 946.21 60.13 873.85 886.08 12.23 1.50 0.39 0.62 0.38 0.2223 0.222 109 926.94 933.64 63.20 863.74 870.44 6.70 3.83 0.29 0.48 0.52 0.577564 0.578 111 926.98 933.92 61.74 865.24 872.18 6.94 2.88 0.15 0.61 0.39 0.16848 0.168 114 926.85 932.83 62.09 864.76 870.74 5.98 3.13 0.24 0.52 0.48 0.360576 0.361 115 922.99 931.91 61.49 861.50 870.42 8.92 4.88 0.23 0.48 0.52 0.583648 0.584 116 927.98 931.93 62.83 865.15 869.10 3.95 7.57 0.28 0.48 0.52 1.102192 1.102 117 921.04 929.37 61.55 859.49 867.82 8.33 3.38 0.21 0.62 0.38 0.269724 0.270 118 926.31 934.63 62.34 863.97 872.29 8.32 3.31 0.27 0.38 0.62 0.554094 0.554 119 928.56 939.56 61.00 867.56 878.56 11.00 6.00 0.32 0.60 0.40 0.768 0.768

CORRELATION-1

WELL NO. 35 WELL NO. 152 WELL NO. 27 WELL NO. 29

WELL NO. 29 WELL NO. 37 WELL NO. 30 WELL NO. 76

CORRELATION-2WELL NO. 153 WELL NO. 125 WELL NO. 86 WELL NO. 155

CORRELATION-3WELL NO. 76 WELL NO. 64 WELL NO. 36 WELL NO. 6

STRUCTURE CONTOUR MAP OF TOP

STRUCTURE CONTOUR MAP OF BOTTOM

CONTOUR MAP OF GROSS THICKNESS

CONTOUR MAP OF NET THICKNESS

CONTOUR MAP OF PHIE

CONTOUR MAP OF SO (Oil Saturation)

METHODOLOGY

The method involves preparation of different contour

maps of the study area and then preparing cross-sections

along the different wells to delineate an overall structure

of the basin. These contour maps were also used in

Volumetric estimation of the Oil Field.

Structure Contour Map was first prepared, using the top

and bottom values of the log data from different wells.

The top and bottom values were corrected using a

parameter known as KB. This map was further used in

preparation of different cross-section along different

wells.

Various cross-sections were prepared vertically,

horizontally and across the study area. Some of them

are;

1. Section through wells 35-152-27-29-37-66-30-76:- It is

an N-S section representing a constant thickness of the

sand unit which towards southern end gets a bit

tapered. The section shows a doming towards the

center which may itself indicate doming of the

basement.

2. Section through wells 153-125-86-130-155:- It is an E-

W section representing sand unit-1. It represents an

anticline which has a steeper western flank and gentler

eastern flank. The thickness almost remains constant.

3. Section Through wells 76-64-36-2-6-73:- It is an SW-NE

trending section which represents again an anticlinal

structure of the study area with western side steeper

and eastern gentler.

Net Thickness (Hp) contour map, Porosity

(Phi) contour map, Oil Saturation (So) maps

were also prepared which were used for

volumetric estimation. The product of

above three parameters gives another

parameter known as Integrated

Hydrocarbon Measures (IHM). A contour

map for IHM is also plotted, which is

generally useful in determining locations

which may show high prospects of oil

accumulation and will act as a guide to

which location are economically ideal for

exploration.

VOLUMETRIC ESTIMATION

Volumetric calculations involve determination of:-

1. First the area of the whole sand unit-1. It

was calculated (by using planimeter) to be

as 35.78 sq km.

2. Secondly areas between successive

contours were calculated (by using

planimeter) for porosity map, oil saturation

map and net thickness map.

DIGITAL PLANIMETER The planimeter is a drafting instrument

used to measure the area of a graphically

represented planar region. The region

being measured may have any irregular

shape, making this instrument remarkably

versatile

Fig: Digital Planimeter

Further calculations can be represented below:-

1) To calculate Average Net Thickness (Hp):-

Contour Interval Midpoint

(a)

Area (sq km)

(b)

Z=(a)x(b)

0-9 4.5 15.812 71.154

9-7 8 5.360 42.880

7-5 6 6.712 40.272

5-3 4 7.896 31.568

Total 35.78 185.874

Average Net Thickness (Hp) = ΣZ ÷ Σ b

Hence Average Net Thickness = 5.1945M

2) To Calculate Average Oil saturation (So):-

Contour Interval Midpoint

(a)

Area(sq km)

(b)

Z=(a)x(b)

0-0.7 0.35 14.78 5.173

0.7-0.6 0.65 6.56 4.264

0.6-0.5 0.55 9.17 5.044

0.5-0.4 0.45 5.27 2.372

Total 35.78 16.853

Average Oil Saturation (So) = ΣZ ÷ Σ b

Hence Average Oil Saturation = 0.471

3) To calculate Average porosity:-

Contour

Interval

Midpoint

(a)

Area(sq km)

(b)

Z=(a)x(b)

0-0.3 0.15 18.184 2.728

0.3-0.25 0.275 7.388 2.032

0.25-0.2 0.225 10.208 2.297

Total 35.78 7.057

Average Porosity (Phi) = ΣZ ÷ Σ b

Hence Average Porosity = 0.1972

Volume of Hydrocarbon (surface)

= Area x Avg. Hp x Avg.Phi x Avg. So x Bo

Where Bo Oil Expansion Factor (1.1) and

depends on a particular oil field.

= 35780000 x 5.1945 x 0.1972 x 0.471 x 1.1

= 18.98 MMm3

Original Oil In place (OIIP)

= Volume of hydrocarbon (Surface) x Density of Oil

= 18.98 x 0.96

= 18.22 MMt

CONCLUSION

• The sand unit makes the reservoir and the shale

body forms the non reservoir part of the study area.

• The sand unit-1 has estimated an OIIP of 18.22 MMt

and volume on surface as 18.98 MMm3

• From the IHM contour map produced one can

conclude other than the northern section of study

area in area around well no. 56 and area around

well no. 93 are good prospecting options which

show IHM values ranging from 1.2 to 2.0.

• The study area is a heterogeneous reservoir and

the oil bearing sand units which were earlier not

perforated may be perforated for additional

production.