Gas Hydrate: A Viable Future Major Energy Resource of India

Abstract

Gas hydrate is a crystalline substance of methane and water, and is found in the shallow sediments of permafrost and outer continental margins. Study of gas hydrate deposits attracted the global attention due to their huge energy potential. Several parameters such as the bathymetry, seafloor temperature, total organic carbon (TOC) content, sediment-thickness, rate of sedimentation, geothermal gradient that control the formation and occurrence of gas hydrate deposits indicate good prospect along the Indian margin. Pockmarks at seafloor or gas escape features such as faulting or gas-chimneys in the shallow sediment offer indirect evidences for gas hydrate. About 1894 trillion cubic meter of gas in the form of gas hydrate is speculated in the Indian offshore, which is more than 1,500 times the country’s present gas reserve. Gas hydrate is thus considered as a viable major energy resource for India. Therefore, the identification and quantification of gas hydrate is very essential. Gas hydrate can make the sediments impervious and thus trap free-gas underneath. Seismic attributes like the reflection strength, blanking, attenuation (Q-1) and instantaneous frequency can be used to identify gas hydrate and free-gas bearing sedimentary strata. The most commonly used marker for gas hydrate is an anomalous seismic reflector, known as the bottom simulating reflector or BSR. Application of these approaches show occurrences of gas hydrate in the Krishna-Godavari (KG), Mahanadi and Andaman regions of the Bay of Bengal, and the Kerala-Konkan and Saurashtra regions of the Arabian Sea. We observe wide-spread occurrences of BSR on the recently acquired seismic data in the Mahanadi and KG regions. Several approaches have been proposed for estimation of gas hydrate based on seismic travel time tomography, full-waveform inversion, amplitude versus offset (AVO) and rock-physics modelling. The data are being utilized for evaluating the resource potential using indigenously developed techniques.