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Anisotropic amplitude variation of the bottom-simulating reflector beneath fracture-filled gas hydrate deposit

DRS at CSIR-National Institute of Oceanography

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Title Anisotropic amplitude variation of the bottom-simulating reflector beneath fracture-filled gas hydrate deposit
 
Creator Sriram, G.
Dewangan, P.
Ramprasad, T.
RamaRao, P.
 
Subject amplitude
anisotropy
gas hydrates
 
Description For the first time, we report the amplitude variation with angle (AVA) pattern of bottom-simulating reflectors (BSRs) beneath fracture-filled gas hydrate deposits when the effective medium is anisotropic. The common depth point (CDP) gathers of two mutually perpendicular multichannel seismic profiles, located in the vicinity of Site NGHP-01-10, are appropriately processed such that they are fit for AVA analysis. AVA analysis of the BSR shows normal-incidence reflection coefficients of -0.04 to -0.11 with positive gradients of 0.04 to 0.31 indicating class IV pattern. The acoustic properties from isotropic rock physics model predict class III AVA pattern which cannot explain the observed class IV AVA pattern in Krishna-Godavari basin due to the anisotropic nature of fracture-filled gas hydrate deposits. We modeled the observed class IV AVA of the BSR by assuming that the gas hydrate bearing sediment can be represented by horizontally transversely isotropic (HTI) medium after accounting for anisotropic wave propagation effects on BSR amplitudes. The effective medium properties are estimated using Backus averaging technique, and the AVA pattern of BSRs is modeled using the properties of overlying HTI and underlying isotropy/HTI media with or without free gas. Anisotropic AVA analysis of the BSR from the inline seismic profile shows 5-30 percent gas hydrate concentration (equivalent to fracture density) and the azimuth of fracture system (fracture orientation) with respect to the seismic profile is close to 45 degrees. Free gas below the base of gas hydrate stability zone is interpreted in the vicinity of fault system.
 
Date 2013-08-07T12:17:22Z
2013-08-07T12:17:22Z
2013
 
Type Journal Article
 
Identifier Journal of Geophysical Research: Solid Earth, vol.118; 2013; 2258-2274
no
http://drs.nio.org/drs/handle/2264/4340
 
Language en
 
Relation J_Geophys_Res_SE_118_2258.jpg
 
Rights An edited version of this paper was published by AGU. Copyright [2013] AGU. To view the published open abstract, go to http://dx.doi.org/10.1002/jgrb.50176
 
Publisher American Geophysical Union