Characterization of Gas Hydrate Deposits in Probable Sandy Facies and Its Related Depositional Processes, East Coast Deep Water Basin, India

Abstract Gas Hydrates represent vast energy resources and are considered to be a potential clean fuel of the future. Under the National Gas Hydrate Program (NGHP), DGH and ONGC have been carrying out research work for exploration and development of the gas hydrates in Indian Offshore. Based on the geological, geophysical and geochemical studies, coring/drilling/logging which were carried out during NGHP-01, 2006 and NGHP-02, 2015, several gas hydrate prospective areas have been identified in Krishna-Godavari (KG) and Mahanadi (MN) deep offshore. During the year 2016-17, the studies have been carried out in the Eastern Offshore areas covering Blocks KD, KG-DWN-98/3, KG-DWN-98/5, KG-DWN-2003/1 and MN-DWN-98/2. In addition to NGHP-01 & NGHP-02 Expeditions, the ongoing studies have identified several new gas hydrate prospects and sites at considerable shallower water depth than NGHP-02. These new prospective areas located at Krishna Godavari (KG), Mahanadi (MN), Cauvery (CY) and Andaman (AN) offshore were identified basing on the site selection criteria established by the site evaluation process for National Gas Hydrate Program, NGHP-02 drilling and builds on successful efforts in recent years to incorporate petroleum system concepts into the specific context of gas hydrate exploration. India's eastern offshore shows favorable conditions for gas hydrate accumulations. Bottom simulating reflectors (BSRs) are widely distributed in vast areas of this basin. This research work is an attempt to identify BSR at ~ 1000 to 2000m water depth for first time, based on the seismic study, characteristics of sedimentary systems, such as their distribution, depositional environments, sedimentary facies, rates of deposition and subsidence, sediment types, and sedimentary discontinuities, which are useful for analyzing the deposition and accumulation conditions of gas hydrates. Using 3D Seismic data in the area of study, depositional features have been identified like deep water fan systems and channel-levee systems in the slope area with sand depocentres. RMS Amplitude and geometrical analyses of depositional systems have been studied in different time windows to evaluate the seismic evidences for gas sourcing and migration, evaluating the depositional environment for occurrence of coarser grain sediments within the gas hydrate stability zone (GHSZ). The study has focused specifically on identification of seismic and geological features that directly support the possible presence of gas hydrates.