Seismic Detection And Quantification Of Gas Hydrates - Application To Indian Continental Margin

Abstract

Global interest in gas hydrates has spread due to their natural occurrences and huge potential as a feasible major energy resource of future. Many countries are pursuing research and development for the exploration and safe production of this new treasure of energy. The bathymetry, seafloor temperature, rate of sedimentation, sedimentary thickness, geothermal gradient and total organic carbon content indicate good prospects of gas hydrates along the Indian margin. By analysing available seismic data, we have identified bottom simulating reflector or BSR, the main marker for gas hydrates, in the Krishna-Godavari, Mahanadi, Andaman, Saurashtra and Kerala-Konkan basins. The drilling and coring by Indian National Gas Hydrates Program have validated the ground truth in the Bay of Bengal (eastern Indian margin). From drilling at one location, we can not categorically rule out the possibility of gas hydrates in the entire Arabian Sea ( we stern Indian margin). Of late, we have acquired multi-channel and ocean-bottom seismic data in deep waters of the Krishna-Godavari and Mahanadi basins. The analysis exhibits wide-spread occurrences of BSRs that coincide with the base of updated gas hydrates stability thickness map, and reveals new prospective zones for gas hydrates in both the basins. We have demonstrated that seismic attributes like the reflection strength, blanking, instantaneous frequency, and attenuation (Q -1 ) can characterize the sediments containing gas hydrates and underlying free gas. For quantification of gas hydrates, we have employed the rock physics modeling to seismic velocities, derived from the traveltime tomography, full-waveform inversion, or amplitude versus offset modeling. As gas hydrates increases and underlying free gas decreases the seismic velocities, the velocity anomaly against the background trend has been utilized for delineating the zones of gas hydrates- and free gas-bearing sediments. We will present these approaches with their application to seismic data in the Bay of Bengal and the Arabian Sea.