Assessment of undiscovered oil and gas resources of the Assam, Bombay, Cauvery, and Krishna-Godavari Provinces, South As

Assessment of Undiscovered Oil and Gas Resources of the Assam, Bombay, Cauvery, and Krishna–Godavari Geologic Provinces, South Asia, 2011

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.

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. 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 (km).

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.

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 km. The Cambay Delta AU includes the failed rift of the Cambay graben and encompasses more than 70,120 km. 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 km. The Mannar Basin AU is also a Mesozoic-age, rifted passive margin, but underwent later compression. It includes about 58,600 km 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 km. Because of paucity of data, the Sri Lanka Shelf AU was not quantitatively assessed in this study.

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 km (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 (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).

Table 1. Assam, Bombay, Cauvery, and Krishna–Godavari Provinces assessment results (undiscovered, technically recoverable, conventional petroleum resources).

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.

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