Seismic characterization of hydrates in faulted, fine-grained sediments of Krishna-Godavari basin: Unified imaging

Abstract

Accepted [Date]; received [Date]; in original form [February 3, 2012] 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 (VP) and attenuation (QP-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) VP and QP-1 variations within the GHSZ. We validate the inverted VP model by reconciling it with a sonic log from a nearby (~250 m) well. The VP 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 QP-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 VP and the QP-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