Gas-hydrates: Indian Scenario

Abstract

At present India produces only one-third of her oil requirements. The escalating demand for energy and the rising price of oil are compelling factors to look for an alternate source of energy for sustainable growth. Gas-hydrates, crystalline form of water and methane, seem to be a viable source of energy. Bathymetry, seafloor temperature, sedimentary thicknesses, rate of sedimentation and total organic carbon (TOC) indicate good prospects of gas-hydrates within the vast offshore regions of India. The energy potential of gas-hydrates is estimated to be twice the energy contained in the total fossil fuel reserves. Several oil companies and national institutes are engaged in gas-hydrate investigations making use of geophysical, geochemical, geological and microbiological data. Based on analysis of available seismic data, geological characteristics, geochemical and microbiological proxies, gas-hydrates have been identified in the continental margins of India (the Bay of Bengal and the Arabian Sea). The drilling and coring under the auspices of the Indian National Gas Hydrates Program (NGHP) has validated the ground truth in the Krishna-Godavari (K-G) and Mahanadi basins and in the Andaman region of the eastern offshore. It is necessary to delineate the gas-hydrates and free-gas bearing sediments and evaluate the resource potential in prospective areas. The National Geophysical Research Institute (NGRI) has built requisite expertise in special processing, modelling and inversion of marine seismic data based on traveltime tomography; waveform inversion; amplitude versus offset (AVO) inversion; AVO attributes and pre-stack depth migration coupled with effective medium theory or rock physics modelling. The blanking, reflection strength, instantaneous frequency and attenuation attributes have been found to be vital for identifying gas-hydrates without BSR and/ or ascertaining whether a BSR is related to gas-hydrates. The traveltime tomography of large offset multi-channel or ocean bottom seismic data can be used for demarcating the zone of gas-hydrates and free-gas bearing sediments. The pre-stack depth migration of seismic data using the large wavelength velocity tomograms may help to understand the genesis of gas-hydrates. All these approaches and their application to available marine seismic data are presented here with a view to investigate gas-hydrates along the continental margins of India.