Gas hydrates have received global attention as a possible major non-conventional energy resource. Therefore, characterization and assessment of gas hydrates are imperative for resource evaluation. Presence of gas hydrates in sediments above the BSR is associated with low attenuation or high quality factor (Q), whereas free gas bearing sediments below the BSR exhibit high attenuation or low seismic Q. We apply the logarithm spectral ratio (LSR) method to marine seismic reflection data in the Krishna-Godavari (KG) basin, where gas hydrates have already been established by drilling/coring. We calculate interval Qs for three sedimentary layers (A, B, and C) bounded by the seafloor, BSR, one reflector above and another reflector below the BSR at some common depth points (CDPs) to study the attenuation characteristics of sediments across the BSR (Fig.1). The estimated average interval Q (160) for the hydrate bearing sediments (layer B) is much higher than the average interval Q (80) for both the loose clayey sediments (Layer A) and underlying free gas saturated sediments (layer C). This demonstrates that estimation of seismic Q can be used for characterization of gas hydrate reservoir.
Fig.1.Variation of Q superimposed on seismic sections along (a) KG-18 and (b) KG-46 lines respectively. Projected location of site 10 is shown by dashed lines on seismic sections. Diamond indicates the cross point.
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V. Jyothi, K. Sain, V. Pandey & A.K. Bhaumik, 2017. Seismic attenuation for characterization of gas hydrate reservoir in Krishna-Godavari basin, eastern Indian margin, Jour. of Geol. Soc. of India, 90, 261-266.