Discovery of natural methane hydrate in deepwater sediments in the east-coast of India have generated significant interest in recent times. This work puts forward a possible relationship of multi-TCF gas accumulation through destabilization of paleo-hydrate in Plio-Pleistocene deepwater channel sands of Krishna-Godavari basin, India. Analysis of gas in the study area establishes its biogenic nature, accumulation of which is difficult to explain using the elements of conventional petroleum system. Gas generated in sediments by methanogenesis is mostly lost to the environment, can however be retained as hydrate under suitable conditions. Longer the time a layer stayed within the gas hydrate stability zone (GHSZ) greater is the chance of retaining the gas which can be later released by change in P-T conditions due to sediment burial. P-T history for selected stratigraphic units from each well is extracted using 1-D burial history model and analyzed. Hydrate stability curves for individual units through time are generated and overlain in P-T space. It transpired that hydrate formation and destabilization in reservoir units of same stratigraphic level in different wells varies both in space and time. Presence of paleo hydrates is confirmed by the occurrence of authigenic carbonate cement and low-saline formation water. We demonstrate how gas released by hydrate destabilization in areas located at greater water depths migrates laterally and updip along the same stratigraphic level to be entrapped in reservoirs which is outside the GHSZ. In areas with isolated reservoirs with poor lateral connectivity, the released gas may remain trapped if impermeable shale is overlain before the destabilization of hydrate. The sequence of geological events which might have worked together to form this gas reservoir is: deposition of organic rich sediments → methanogenesis → gas hydrate formation → destabilization of hydrate and release of gas → migration and entrapment in reservoirs.

Studies of geologic and geophysical data from the offshore of India have revealed two geologically distinct areas with inferred gas hydrate occurrences: the passive continental margins of the Indian Peninsula and along the Andaman convergent margin. The Indian National Gas Hydrate Program (NGHP) Expedition 01 was designed to study the occurrence of gas hydrate 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 in these two diverse settings. NGHP Expedition 01 established the presence of gas hydrates in Krishna- Godavari, Mahanadi and Andaman basins. The expedition discovered one of the richest gas hydrate accumulations yet documented (Site 10 in the Krishna-Godavari Basin), documented the thickest and deepest gas hydrate stability zone yet known (Site 17 in Andaman Sea), and established the existence of a fully-developed gas hydrate system in the Mahanadi Basin (Site 19).