Gas hydrate saturation from heterogeneous model constructed from well log in Krishna–Godavari Basin, Eastern Indian Offshore

Abstract

The occurrence of gas hydrate in shallow marine sediments causes an increase of seismic velocity compared to that of water saturated host sediments. This increase of velocity depends on the spatial distribution of hydrates in pore spaces of sediments. Velocities derived from seismic data are low frequency effective values, which cannot be uniquely related to high frequency variation in the rock property. Characterisation of a gas hydrate reservoir from seismic data generally assumes homogeneous distribution of gas hydrates, which leads to overestimation of gas hydrate saturation. Contrary to this, we record higher resolution seismic velocities in well log that lead to characterisation of small scale heterogeneities due to fine scale distribution of gas hydrate in sediments. Here, we incorporate these small scale heterogeneities of gas hydrate reservoir by generating 2-D random stochastic heterogeneous velocity and density fields using well log data in the Krishna–Godavari (KG) basin, eastern Indian offshore. These simulated fields do not contain any information about phase distribution but include all heterogeneities of the reservoir in the well log scale. We demonstrate that the amount of gas hydrate estimated from seismic data is indeed higher (∼12.12 per cent of pore volume) than that obtained from simulated 2-D heterogeneous velocity and density models (∼9.60 per cent of pore volume) along the seismic line.