U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3059

May 2012

World Petroleum Resources Project

Assessment of Undiscovered Oil and Gas Resources of the Assam, Bombay, 

Cauvery, and Krishna–Godavari Geologic Provinces, South Asia, 2011

Printed on recycled paper

Introduction

The U.S. Geological Survey (USGS) estimated 

volumes of undiscovered, technically recoverable, conventional oil and gas resources of the Assam, Bombay, 

Cauvery, and Krishna–Godavari Provinces, South Asia. 

The assessment is part of a project to estimate petroleum 

resources for priority basins around the world, specifically 

for total petroleum systems (TPS). Assessment units 

(AU) are defined on the basis of their geologic attributes 

that are favorable for the generation and accumulation of 

petroleum. This assessment was based on data provided 

by the Indian Directorate General of Hydrocarbons, 

published geologic information, commercial data from 

oil and gas wells and fields, and field production records.

Total Petroleum Systems and Assessment Units

Assam Province

The Assam Province is in northeastern India and 

northwestern Myanmar (fig. 1). The province is interpreted 

to have originated as a Mesozoic rifted passive margin, 

but evolved into a foreland basin during the Neogene, 

when the Indian plate collided with the Eurasian continent. 

INDIA

CHINA

IRAN

PAKISTAN

MYANMAR

AFGHANISTAN

Thailand

NEPAL

OMAN

LAOS

BANGLADESH

BHUTAN

BOMBAY

SHELF AU

MANNAR

BASIN AU

KRISHNA–

GODAVARI

BASIN AU

CENOZOIC

RESERVOIRS AU

CAMBAY

DELTA AU

NORTHERN

CAUVERY

BASIN AU

80° 90°

20°

10°

30°

60° 70° 100°

® INDIA

Sri

Lanka

BOMBAY

PROVINCE

CAUVERY

PROVINCE

KRISHNA–

GODAVARI

PROVINCE

ASSAM

PROVINCE

Kutch

graben

SRI LANKA

SHELF AU

0 200 400 KILOMETERS 

0 150 200 MILES

SRI

LANKA

 Using a geology-based assessment methodology, the U.S. Geological Survey estimated volumes of undiscovered, technically 

recoverable, conventional petroleum resources for the Assam, Bombay, Cauvery, and Krishna–Godavari Provinces,* South Asia. The 

estimated mean volumes are as follows: (1) Assam Province, 273 million barrels of crude oil, 1,559 billion cubic feet of natural gas, and 

43 million barrels of natural gas liquids; (2) Bombay Province, 1,854 million barrels of crude oil, 15,417 billion cubic feet of natural gas, 

and 498 million barrels of natural gas liquids; (3) Cauvery Province, 941 million barrels of crude oil, 25,208 billion cubic feet of natural 

gas, and 654 million barrels of natural gas liquids; and (4) Krishna–Godavari Province, 466 million barrels of crude oil, 37,168 billion 

cubic feet of natural gas, and 484 million barrels of natural gas liquids. The totals for the four provinces are 3,534 million barrels of

crude oil, 79,352 billion cubic feet of natural gas, and 1,679 million barrels of natural gas liquids.

Figure 1. Generalized map 

showing the boundaries of 

the Bombay Shelf, Cambay 

Delta, Cenozoic Reservoirs, 

Krishna–Godavari Basin, 

Northern Cauvery Basin, Mannar 

Basin,and Sri Lanka Shelf 

assessment units (modified 

from Wandrey, 2004a, b). The 

Sri Lanka Shelf assessment unit 

was not quantitatively assessed 

in this study. Inset map shows 

locations of Bombay, Assam, 

Cauvery, and Krishna–Godavari 

Provinces (Wandrey and Law, 

1998). Dashed boundaries 

indicate lines of control and area 

of Indian claim.

*The term “provinces” refers to geologically defined units 

accessed by USGS for the purposes of this report and carries no 

political or diplomatic connotation.
These tectonic events controlled the distribution of Paleogene source rocks, as well as the oil and gas accumulations 

(Wandrey, 2004a). The Cenozoic Composite TPS was 

defined for the Assam Province (table 1), which includes 

petroleum source rocks ranging in age from Eocene to 

Oligocene. The Cenozoic Reservoirs AU, containing conventional undiscovered oil and gas resources, was defined 

geologically within the Assam Province and encompasses 

more than 42,300 square kilometers (km2).

Bombay Province

The Bombay Province, located along the northwestern coast of India (fig. 1), includes a rifted passive margin 

comprising a marine shelf, carbonate platform, and rift/sag 

basins. These structures were used to define the Bombay 

Shelf AU and the Cambay Delta AU (Wandrey, 2004b). 

The Bombay Shelf AU includes the Bombay structural 

high and part of a failed rift system of the Kutch graben 

and encompasses more than 180,140 km2. The Cambay 

Delta AU includes the failed rift of the Cambay graben 

and encompasses more than 70,120 km2. Source rocks are 

correlative between the two AUs, therefore, one Mesozoic−

Cenozoic Composite TPS was defined for both the Bombay 

Shelf and Cambay Delta AUs (table 1).

Cauvery Province

The Cauvery Province is located along the southeastern coast of India and includes coastal parts of Sri Lanka 

(fig. 1). The Mesozoic−Cenozoic Composite TPS was 

defined for the province. The Northern Cauvery Basin 

AU, the Mannar Basin AU, and the Sri Lanka Shelf AU 

were delineated by major structures. The Northern Cauvery Basin AU is a Mesozoic-age, rifted passive margin 

that encompasses more than 80,090 km2. The Mannar 

Basin AU is also a Mesozoic-age, rifted passive margin, 

but underwent later compression. It includes about 

58,600 km2 and is separated from the Northern Cauvery 

Basin AU by an arch extending from India to Sri Lanka 

(fig. 1). The Sri Lanka Shelf AU is located along the east 

side of the Sri Lanka block and encompasses approximately 22,590 km2

. Because of paucity of data, the Sri 

Lanka Shelf AU was not quantitatively assessed in this 

study.

Krishna–Godavari Province

The Krishna–Godavari Province is a rifted passive 

margin along the eastern coast of India (fig. 1). A 

Mesozoic−Cenozoic Composite TPS was defined for the 

province; however, the source rocks are of somewhat 

different ages than those in the neighboring Cauvery 

Province. The Krishna–Godavari Basin AU encompasses 

the the entire province and is an area of approximately 

109,070 km2 (fig. 1).

Assessment Results

Estimates of volumes of undiscovered, technically 

recoverable, conventional oil and gas resources are listed 

in table 1. No attempt was made to estimate economically 

recoverable resources. The estimated mean volumes for 

the Cenozoic Reservoirs AU of the Assam Province are 

approximately 273 million barrels (MMB) of crude oil, 

1,559 billion cubic feet (BCF) of natural gas (568 BCF 

of associated and dissolved natural gas and 991 BCF of 

nonassociated natural gas), and 43 MMB of natural gas 

liquids (26 MMB of natural gas liquids in oil accumulations and 17 MMB of total liquids in nonassociated gas 

accumulations).

The estimated mean volumes for the Bombay Province are about 1,854 MMB of crude oil, 15,417 BCF 

of natural gas (4,710 BCF of associated and dissolved 

natural gas and 10,707 BCF of nonassociated natural gas), 

and 498 MMB of natural gas liquids (55 MMB of natural 

gas liquids in oil accumulations and 443 MMB of total 

liquids in nonassociated gas accumulations). The volumetric contributions from each AU are (1) Bombay Shelf AU, 

approximately 1,449 MMB of crude oil, 13,579 BCF of 

natural gas (3,986 BCF of associated and dissolved natural gas and 9,593 BCF of nonassociated natural gas), and 

447 MMB of natural gas liquids (35 MMB of natural gas 

liquids in oil accumulations and 412 MMB of total liquids 

in nonassociated gas accumulations); and (2) Cambay 

Delta AU, about 405 MMB of crude oil, 1,838 BCF of 

natural gas (724 BCF of associated and dissolved natural 

gas and 1,114 BCF of nonassociated natural gas), and 

51 MMB of natural gas liquids (20 MMB of natural gas 

liquids in oil accumulations and 31 MMB of total liquids 

in nonassociated gas accumulations).

The estimated mean volumes for the Cauvery Province 

are approximately 941 MMB of crude oil, 25,208 BCF of 

natural gas (3,255 BCF of associated and dissolved natural gas and 21,953 BCF of nonassociated natural gas), and 

654 MMB of natural gas liquids (82 MMB of natural gas 

liquids in oil accumulations and 572 MMB of total liquids 

in nonassociated gas accumulations). The volumetric 

contributions from each AU are as follows: (1) Northern 

Cauvery Basin AU approximately 458 MMB of crude oil, 

12,979 BCF of natural gas (1,585 BCF of associated and 

dissolved natural gas and 11,394 BCF of nonassociated 

natural gas), and 337 MMB of natural gas liquids (40 MMB 

of natural gas liquids in oil accumulations and 297 MMB 

of total liquids in nonassociated gas accumulations); and 
Table 1. Assam, Bombay, Cauvery, and Krishna–Godavari Provinces assessment results (undiscovered, technically recoverable, conventional 

petroleum resources). 

[MMB, million barrels; BCF, billion cubic feet. Results shown are fully risked estimates. For gas fields, all liquids are included under the natural gas liquids (NGL) 

category. F95 denotes a 95-percent chance of at least the amount tabulated. Other fractiles are defined similarly. Fractiles are additive under the assumption of perfect 

positive correlation. TPS, total petroleum system; AU, assessment unit. Gray shading indicates not applicable]

Assam, Bombay, Cauvery, and Krishna–Godavari Provinces

Total undiscovered petroleum

resources 3,534 79,352 1,679

Total undiscovered resources Total petroleum systems

(TPS)

and assessment units (AU)

Field

type Oil (MMB) Gas (BCF) NGL (MMB)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Mean (expected)

largest

field size

(MMB or BCF)

Gas

Oil

Cenozoic Reservoirs AU

Assam Province, Cenozoic Composite TPS

151 261 436 273 297 542 936 568 14 25 43 26

550 949 1,579 991 8 16 29 17

23

92

Gas

Oil

Bombay Shelf AU

1,449 3,986 35

9,593 412

857 1,388 2,257 2,298 3,821 6,264 20 34 55

5,573 9,182 14,962 238 394 645

24

271

Bombay Province, Mesozoic–Cenozoic Composite TPS

Total undiscovered petroleum

resources 1,854 15,417 498

Gas

Oil

Cambay Delta AU

405 724 20

1,114 31

259 394 588 427 697 1,111 11 19 30

621 1,068 1,769 14 28 58

29

186

Total undiscovered petroleum

resources 466 37,168 484

Gas

Oil

Northern Cauvery Basin AU

458 1,585 40

11,394 297

274 440 705 908 1,520 2,485 23 39 63

6,407 10,922 18,010 164 284 473

22

755

Cauvery Province, Mesozoic–Cenozoic Composite TPS

Total undiscovered petroleum

resources 941 25,208 654

Gas

Oil

Mannar Basin AU

483 1,670 42

10,559 275

234 451 837 762 1,554 2,969 19 39 76

5,222 9,897 18,153 133 258 477

59

905

Oil

Krishna–Godavari Basin AU

466 1,746 53

35,422 431

262 448 737 919 1,668 2,843 28 51 87

15,792 33,088 63,273 154 367 915

46

6,908

Krishna–Godavari Province, Mesozoic–Cenozoic Composite TPS

Gas

Total undiscovered petroleum

resources 273 1,559 43
(2) Mannar Basin AU, about 483 MMB of crude oil, 12,229 

BCF of natural gas (1,670 BCF of associated and dissolved natural gas and 10,559 BCF of nonassociated natural gas), and 317 MMB of natural gas liquids (42 MMB of 

natural gas liquids in oil accumulations and 275 MMB of 

total liquids in nonassociated gas accumulations).

The estimated mean volumes for the Krishna–

Godavari Basin AU of the Krishna–Godavari Province are 

approximately 466 million barrels (MMB) of crude oil, 

37,168 billion cubic feet (BCF) of natural gas (1,746 BCF 

of associated and dissolved natural gas and 35,422 BCF of 

nonassociated natural gas), and 484 MMB of natural gas 

liquids (53 MMB of natural gas liquids in oil accumulations and 431 MMB of total liquids in nonassociated gas 

accumulations).

For Further Information

Supporting geologic studies of total petroleum 

systems and assessment units, and reports on the methodology used in the assessment of the Assam, Bombay, 

Cauvery, and Krishna–Godavari Provinces, as well as 

the assessment results, are available at the USGS Energy 

website: http://energy.usgs.gov.

Assam, Bombay, Cauvery, and Krishna–

Godavari Provinces Assessment Team

T.R. Klett (tklett@usgs.gov), Christopher J. Schenk, 

Craig J. Wandrey, Ronald R. Charpentier, Troy A. Cook, 

Michael E. Brownfield, Janet K. Pitman, and Richard M. 

Pollastro.

References Cited

Wandrey, C.J., and Law, B.E., 1998, Map showing 

geology, oil and gas fields, and geologic provinces of 

South Asia: U.S. Geological Survey Open-File Report 

97–470C, CD–ROM.

Wandrey, C.J., 2004a, Sylhet−Kopili/Barail−Tipam 

Composite Total Petroleum System, Assam Geologic 

Province, India: U.S. Geological Survey Bulletin 2208-D, 

19 p.

Wandrey, C.J., 2004b, Bombay geologic province Eocene 

to Miocene composite total petroleum system, India: 

U.S. Geological Survey Bulletin 2208-F, 20 p.