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

Abstract

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 × 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 (∼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.