Seismic characterization of hydrates in faulted, fine‐grained sediments of Krishna‐Godavari Basin: Full waveform inversion

In fine-grained, faulted sediments, both stratigraphic and fault-induced structural variations can simultaneously determine the gas hydrate distribution. Insights into hydrate distribution can be obtained from P wave velocity (V-P) and attenuation (Q(P)(-1)) character of the gas hydrate stability zone (GHSZ). In this paper, we apply frequency domain full-waveform inversion (FWI) to surface-towed 2D multichannel seismic data from the Krishna-Godavari (KG) Basin, India, to image the fine-scale (100 x 30 m) V-P and Q(P)(-1) variations within the GHSZ. We validate the inverted V-P model by reconciling it with a sonic log from a nearby (similar to 250 m) well. The V-P model shows a patchy distribution of hydrate. Away from the faults-dominated parts of the profile, hydrates demonstrate stratigraphic control which appears to be permeability driven. The Q(P)(-1) model suggests that attenuation is relatively suppressed in hydrates-bearing sediments. Elevated attenuation in non-hydrate-bearing sediments could be driven by the apparent pore fluid immiscibility at seismic wavelengths. The V-P and the Q(P)(-1) models also suggest that fault zones within the GHSZ can be hydrate-or free-gas-rich depending on the relative supply of free gas and water from below the GHSZ.