Seismic studies of gas hydrate in the KG Basin, East Sea, offshore India

Abstract

India has developed an ambitious research program after successfully unearthing gas hydrate layer at site 10 in Krishna Godavari (KG) Offshore, during first National Gas Hydrate Program (NGHP-1). After studying the result from NGHP-1, second NGHP has been firmed up with an objective to identify the Gas Hydrate prospect for test drilling using seismic data and well analysis in KG offshore areas. First time a 3D seismic data volume has been studied with objective to identify Gas Hydrate prone areas in Indian water. To achieve this objective seismic data has been calibrated with well log to identify the Top and bottom of Gas Hydrate Stability Zone. The extent of Gas hydrate is inferred on seismic section by large amplitude (opposite polarity of with respect to Sea bottom) bottom simulating reflector (BSR), which is following the sea bottom and also at places cutting across dipping srata. In this study, the BSR mapped and then RMS amplitude extracted within window of 100ms above of it. RMS amplitude distribution suggests the variance in Gas hydrate concentration spatially primarily guided by the porosity variation in shape of channel and scroll bar. Further RMS amplitude extraction 20 ms below BSR suggest the presence of free gas areas associated with Gas hydrate in the down dip towards the regional lows. The study concludes that there are three to four areas where positive acoustic impedance within GHSZ is available, probably indicative of high Gas Hydrate concentration due to better reservoir condition and may be tested.