Gas hydrates in India: Potential and development

Abstract

The shallow sediments along the Indian continental margin are good hosts for gas hydrates, and the methane within gas hydrates has been prognosticated as more than 1500 times of India's present natural gas reserve. Production of even 10% from this natural reserve is sufficient to meet country's vast energy requirement for about a century. Hence, it was felt necessary to map the most prospective zones of gas hydrates and evaluate their energy potential along the Indian margin. First of all, we have updated the gas hydrates stability thickness map along the Indian shelf to provide the spatial and depth domains within which gas hydrates can be looked for. We have identified the bottom simulating reflectors (BSRs), the main marker for gas hydrates, in the Krishna–Godavari (KG), Mahanadi, Andaman, Kerala–Konkan, and Saurashtra regions respectively. The total organic carbon content (TOC), sediment thickness and rate of sedimentation indicate that the Cauvery and Kerala–Laccadive basins are also prospective for gas hydrates. Seismic attenuation (Q− 1), reflection strength, instantaneous frequency and blanking have been computed to characterize the sediments containing gas hydrates and free-gas. The faulting or gas-chimneys have also been used for the identification of gas hydrates. We have developed several approaches based on seismic traveltime tomography, full-waveform inversion, amplitude versus offset (AVO) modeling and AVO attributes each coupled with rock-physics modeling, and utilized them for the quantification of gas hydrates. A large volume of multi-channel and ocean bottom seismic data have been acquired in 2010 between 500 to 2500 m water depths in KG and Mahanadi basins. The new data exhibit wide-spread occurrences of BSRs; reveal new prospective zones of gas hydrates; and are being modeled for the delineation of sediments hosting gas hydrates, and evaluation of their resource potential. Efforts are on to develop suitable technology for exploitation. We anticipate that free-gas lying below gas hydrate-bearing sediments can be produced economically in near future. However, it may take longer time to retrieve gas from gas hydrates.