Relating AVO Signatures of Bottom Simulating Reflectors to Gas Venting Structures

摘要

The base of gas hydrates over the continental margins has been found to be coincident with a characteristic seismic reflector termed as bottom simulating reflector (BSR). Off late the occurrence of two BSRs have been reported from many regions of the world. In this study we estimate uncertainty inAmplitude versus Offset (AVO) behavior of the single BSR and double bottom simulating reflector (DBSR) observed over two geological provinces; Kerala-Konkan Basin, offshore India and Green Canyon offshore USA. Anomalous behavior of seismic velocities within the GHSZ is associated with the occurrence of DBSR, low amplitude seismic chimneys and bright spots, indicating increased hydrate concentration at DBSR location and fluid venting structures underneath. Such structures extend upward into the regional GHSZ through discrete fracture network and sometimes allow methane to escape into the ocean. Our analysis indicates that the variability inAVO signatures for gas hydrate saturated sediments is somehow linked to the discrete zones of steeply inclined fractures which are responsible for the migration of deep gas and its escape through the seabed.