Research paper
Geologic implications of gas hydrates in the offshore of India: Krishna–Godavari Basin, Mahanadi Basin, Andaman Sea, Kerala–Konkan Basin

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Abstract

Gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates. Gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the “gas hydrate petroleum system” that control the occurrence of gas hydrates in nature. The primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of India and to document the application of the petroleum system approach to the study of gas hydrates.

National Gas Hydrate Program of India executed the National Gas Hydrate Program Expedition 01 (NGHP-01) in 2006 in four areas located on the eastern and western margins of the Indian Peninsula and in the Andaman Sea. These areas have experienced very different tectonic and depositional histories. The peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of Gondwanaland to form the present Indian Ocean. The Andaman Sea is bounded on its western side by a convergent margin where the Indian plate lithosphere is being subducted beneath southeast Asia.

NGHP-01 drilled, logged, and/or cored 15 sites (31 holes) in the Krishna–Godavari Basin, 4 sites (5 holes) in the Mahanadi Basin, 1 site (2 holes) in the Andaman Sea, and 1 site (1 hole) in the Kerala–Konkan Basin. Holes were drilled using standard drilling methods for the purpose of logging-while-drilling and dedicated wireline logging; as well as through the use of a variety of standard coring systems and specialized pressure coring systems.

NGHP-01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the Krishna–Godavari Basin, the Mahanadi Basin, and in the Andaman Sea. The site drilled in the Kerala–Konkan Basin during NGHP-01 did not yield any evidence of gas hydrate. Most of the downhole log-inferred gas hydrate and core-recovered gas hydrate were characterized as either fracture-filling in clay-dominated sediments or as pore-filling or grain-displacement particles disseminated in both fine- and coarse-grained sediments. Geochemical analyses of gases obtained from sediment cores recovered during NGHP-01 indicated that the gas in most all of the hydrates in the offshore of India is derived from microbial sources; only one site in the Andaman Sea exhibited limited evidence of a thermogenic gas source. The gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of India.

Section snippets

Editor's note

This report is part two of a two-report series that summarizes the results of the Indian National Gas Hydrate Program Expedition 01 (NGHP-01). This report (Kumar et al., 2014) in this series reviews the occurrence and geologic controls on gas hydrates in the Krishna–Godavari Basin, the Mahanadi Basin, the Andaman Sea, and the Kerala–Konkan Basin, while the first report in this series summarizes the overall operational and scientific accomplishments of NGHP-01 (Collett et al., 2014).

Krishna–Godavari Basin

The Krishna–Godavari Basin is a proven petroliferous basin along the east coast of India. The onshore portion of the basin covers an area of approximately 15,000 km2, while the offshore portion covers an area of at least 25,000 km2 extending seaward to the 1000 m isobath. The basin contains sediments about 5-km thick with several depositional sequences, ranging in age from Late Carboniferous to Pleistocene (Curray et al., 1982).

The eastern continental margin of India formed as the result of

Site NGHP-01-02

Site NGHP-01-02 (Prospectus Site KGGH03-A) is located at the far southwestern margin of the Krishna–Godavari Basin study area (Fig. 1). The water depth at this site is ∼1058 m. This site was not cored; only LWD data were obtained from two holes. The seismic-imaged stratigraphy at this site is characterized by a ridge with steeply dipping stratigraphy (Fig. 2). The depth of the seismic-identified bottom-simulating reflector (BSR) at this site was estimated at ∼171 mbsf.

The LWD-acquired

NGHP-01 scientific reporting

NGHP-01 provided the data and information needed to characterize the lithostratigraphic controls on the occurrence of gas hydrate, physical properties of gas hydrate-bearing sediments, interstitial water and gas geochemistry, and microbiology of the gas hydrate systems in the Krishna–Godavari Basin, the Mahanadi Basin, the Andaman Sea, and the Kerala–Konkan Basin. NGHP-01 also yielded important information on the well log and geophysical properties of gas hydrate-bearing sediments in each basin

Gas hydrate petroleum systems analysis

In recent years, significant progress has been made in addressing key issues on the formation, occurrence, and stability of gas hydrate in nature. The concept of a gas hydrate petroleum system, similar to the concept that guides conventional oil and gas exploration, has been developed to systematically assess the geologic controls on the occurrence of gas hydrate in nature (Collett et al., 2009). In a gas hydrate petroleum system, the individual factors that contribute to the formation of gas

Conclusion

The Indian National Gas Hydrate Program Expedition 01 (NGHP-01) was designed to study the gas hydrate occurrences off the Indian Peninsula and along the Andaman convergent margin with special emphasis on understanding the geologic and geochemical controls on the occurrence of gas hydrate. Drilling of both a passive and convergent continental margin on the same expedition also allowed for the comparison of the geologic factors believed to control the occurrence of gas hydrate in these two

Acknowledgment

The editors wish to thank those that contributed to the success of the National Gas Hydrate Program Expedition 01 (NGHP-01). NGHP-01 was planned and managed through collaboration between the Directorate General of Hydrocarbons (DGH) under the Ministry of Petroleum and Natural Gas (India), the U.S. Geological Survey (USGS), and the Consortium for Scientific Methane Hydrate Investigations (CSMHI) led by Overseas Drilling Limited (ODL) and FUGRO McClelland Marine Geosciences (FUGRO). The platform

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