Identifying gas hydrate prospects offshore India

Authors: Collett, Timothy S. (speaker: Winters, Bill, U.S. Geological Survey).

Venue: India’s Directorate General of Hydrocarbons’ International Conference on Gas Hydrates in Nodia (New Delhi), India, February 6–8, 2008 (http://www.dghindia.org/site/pdfattachments/upcomingevents/Updated_Programme_gAS[1].pdf [PDF-external site]).

Abstract: The primary goal of the Indian National Gas Hydrate Program (NGHP) Expedition 01 was to conduct scientific ocean drilling/coring, logging, and analytical activities to assess the geologic occurrence, regional context, and characteristics of gas hydrate deposits along the continental margins of India. The overarching objective is to meet the long-term goal of exploiting gas hydrates as a potential energy resource in a cost-effective and safe manner. During its 113.5-day voyage, the JOIDES Resolution cored or drilled 39 holes at 21 sites (one site in Kerala-Konkan, 15 sites in Krishna-Godavari, four sites in Mahanadi, and one site in Andaman deepwater areas), penetrated more than 9,250 meters of section, and recovered nearly 2,850 meters of core with ~78% recovery. Twelve holes were logged with logging-while-drilling tools, and an additional 13 holes were wireline logged. NGHP Expedition 01 established the presence of gas hydrates in Krishna-Godavari, Mahanadi, and Andaman basins. NGHP Expedition 01 was among the most complex and comprehensive methane hydrate field ventures yet conducted. The science team utilized extensive on-board lab facilities to examine and prepare preliminary reports on the physical properties, geochemistry, and sedimentology of all the data collected prior to the end of the expedition. Although the data will continue to inform gas hydrates science for years to come, the following are the key scientific highlights of the expedition to date:

• Conducting comprehensive analyses of gas-hydrate-bearing marine sediments in both passive continental margin and marine accretionary wedge settings.
• Determining that the calculated depth to the base of the methane hydrate stability zone, as derived from downhole temperature measurements, closely matches the depth of the seismically identified bottom simulating reflectors at most of the sites established during this expedition.
• Discovering gas hydrate in numerous complex geologic settings and collecting an unprecedented number of gas hydrate cores.
• Characterizing most of the recovered gas hydrate as either pore-filling grains, particles disseminated in coarser grain sediments, or as a fracture-filling material in clay-dominated sediments.
• Ascertaining that the occurrence of concentrated gas hydrate is mostly controlled by the presence of fractures and/or coarser-grained (mostly sand-rich) sediments.
• Finding gas hydrates occurring in “combination reservoirs” consisting of horizontal or subhorizontal coarse-grained permeable sediments (sands, for the most part) and apparent vertical to subvertical fractures that provide the conduits for gas migration.
• Delineating and sampling one of the richest marine gas hydrate accumulations yet discovered (Site NGHP-01-10 in the Krishna-Godavari Basin).
• Discovering one of the thickest and deepest gas hydrate occurrences yet known (offshore the Andaman Islands, Site NGHP-01-17), which revealed gas-hydrate-bearing volcanic ash layers as deep as 600 meters below the seafloor.
• Establishing the existence of a fully developed gas hydrate system in the Mahanadi basin of the Bay of Bengal.
• Determining that most of the gas hydrate occurrences discovered during this expedition appear to contain mostly methane generated by microbial processes. However, there is also evidence of thermal origin for a portion of the gas within the hydrates of the Mahanadi Basin and the Andaman offshore area.
• Postulating that gas hydrate in the Krishna-Godavari Basin appears to be closely associated with large-scale structural features, in which the flux of gas through local fracture systems, generated by the regional stress regime, controls the occurrence of gas hydrate.

Related NETL Project
The USGS conducts scientific studies of natural gas hydrates to support DOE efforts to evaluate and understand methane hydrates, their potential as an energy resource, and the hazard they may pose to ongoing drilling efforts. This project, DE-AI26-05NT42496, extends USGS support to the DOE Methane Hydrate Research Program previously supported under DE-AT26-97FT34342 and DE-AT26-97FT34343.

NETL Project Contacts
NETL – Robert Vagnetti (robert.vagnetti@netl.doe.gov or 304-285-1334)
USGS – Deborah R. Hutchinson (dhutchinson@usgs.gov or 508-457-2263)