Occurrence of gas hydrates along the continental margins of India, particularly the Krishna-Godavari offshore basin

Abstract

The presence of gas hydrates along the Indian continental margins has been inferred mainly from the bottom simulating reflection/reflector (BSR) and the gas hydrate stability zone thickness map of India. Multidisciplinary investigations have been carried out in the Krishna-Godavari offshore area along the eastern continental margin of India, which is known for its hydrocarbon potential. Processed multibeam data provided a high-resolution seafloor mosaic with a fine scale geomorphology. Deep tow digital side scan sonar, multi frequency chirp sonar and 3.5 KHz sub-bottom profiler records depict various kinds of gas escape features over the regions where BSRs are prominent. Geochemical analyses of the 5 m-long cores show a general decrease trend in the porewater sulphate concentration, while the gas chemistry reveals an increase trend of methane concentration with core depth. Total Organic Carbon varies from 0.6 to greater than 2.0% and CaCO sub(3) from 5.0 to greater than 29%. Observed geophysical, geochemical and microbial proxies suggest the likely presence of gas hydrates in the Krishna-Godavari offshore area. Recent drilling work carried out onboard JOIDES Resolution confirmed the presence of massive (greater than 80 m thick) accumulation of gas hydrates, and fully developed gas hydrate system in the Mahanadi offshore area and the Andaman Sea.