Gas hydrate/free gas migration pathways in submarine slope failures: East Indian Margin

Abstract

Gas hydrates from the continental margin settings are mostly confined to continental slopes. The free gas occurring below the gas hydrate laden sediments play a crucial role in the submarine slope failures and can potentially trigger the submarine landslides. The present study is carried out to investigate such a scenario in the shale dominated Krishna–Godavari (KG) basin having proven gas hydrate deposits. Shale reservoirs are less permeable compared to sandstone reservoirs and as such, the free gas that is locked in the pore spaces of shales would eventually create hydro fractures or faults to escape from the pore spaces. This overpressure from the gas zone will find a pathway to reach the shallower depths. In the present study, two faults are identified of which, one is acting as a potential pathway for overpressures to travel through it, while the other is found to be critically pressurized due to the gas zone below it. The calculated gas column height is ~51 m and any further increase in the gas column height would create a fault slip and cause the mechanical failure of the sediments, creating another potential pathway. We infer that these faults are acting as a migration pathway in our study area and the advection of fluid/gas from the gas zone via the pathway might have played a major role in creating a slope break above the fault.