Gas hydrate-related proxies inferred from multidisciplinary investigations in the Indian offshore areas

The presence of gas hydrates along the Indian continental margins has been speculated by earlier workers based on the identification of Bottom Simulating Reflection (BSR) on the multichannel seismic reflection records and computed gas hydrate stability zone thickness map. The BSR alone is inadequate to infer gas hydrates as suggested by drilling results elsewhere. Therefore, to understand the subsurface distribution of gas bydrates along the continental margins of India, multidisciplinary investigations have been undertaken. The observed geophysical anomalies (BSRs, pockmarks, gas upthrust zones, vents, blanking zones, etc.) in association with the geochemical (sulphate reduction trend and increase in methane flux with core depth) and microbiological proxy indicators (sulphate and nitrate-reducing bacteria, and fermenters) favour the presence of gas hydrates in some of the Indian offshore regions.