Gas hydrate saturation from seismic data constrained by log data in the Krishna-Godavari Basin

A strong bottom simulating reflector (BSR) was observed along seismic line transect across site NGHP-01-05 having characteristic reverse polarity with respect to seafloor, cross-cutting of dipping strata, and high reflectivity below the BSR. The observed BSR depth along seismic profile varies from similar to 100 to similar to 125 mbsf. Gas hydrate was recovered during coring and drilling at this site during National Gas Hydrate Drilling Expedition-01 of India. Recovered pressure cores at discrete depths within gas hydrate stability zone from site NGHP-01-05 shows similar to 0.6-9.4 % pore volume of methane hydrate. Gas hydrate saturation was estimated along seismic profile constrained by observed velocity and density log to introduce model-based acoustic impedance inversion. It was observed that each stacked trace amplitude converted to acoustic log as a product of velocity and density. During the impedance inversion process inverted vealocity log was observed at each and every trace act as an individual log. Gs hydrate saturation was estimated from inverted velocity coupled with effective medium rock physics modeling. The estimated gas hydrate saturation from the post-stack acoustic impedance inversion velocity along 2D seismic profile varies up to 15-20 % of the pore space. The gas hydrate saturation estimated from electrical resistivity log and core data shows maximum 20 % pore spaces saturated with gas hydrate from anisotropic modeling, which is comparable to gas hydrate saturation along seismic profile estimated from inverted velocity constrained by logs.