AVA Analysis of BSR in Fractured filled Gas-hydrates Reservoir in Krishna-Godavari Basin, India

Abstract

Abstract Gas-hydrates, a major unconventional energy resources of the future, are delineated by seismic experiment through the identification of an anomalous reflector, known as the bottom simulating reflector or BSR on seismic data. The amplitude variation with angle (AVA) from the BSR can be used for quantitative assessment of gas-hydrates and free-gas across the BSR. We have performed the AVA analysis of BSR in the Krishna Godavari (KG) basin of India, where gas-hydrates have been recovered in fractured shale by Exp-01 of Indian National Gas Hydrates Program. The study shows negative intercept and positive gradient along two perpendicular seismic lines, one passing through the well at site-10 of Exp-01. The intercept of -0.01 to -0.15 and gradient of 0.01 to 0.4 are interpreted as class-IV anomaly, which is due to anisotropy caused by fractures filled with gas-hydrates. We have modelled the observed AVA pattern using anisotropic equation for horizontally symmetric transversally isotropic (HTI) media in which gas-hydrates occur in the fractures, roughly aligned at angle of 45° above the BSR and patchy gas distribution below the BSR. The results show 0-31% variable gas-hydrates in fractured morphology and 0-11% free gas below the BSR respectively.