NDLI: Velocity and AVO analysis for the investigation of gas hydrate along a profile in the western continental margin of India

Content Provider	Springer Nature Link
Author	Dewangan, Pawan Ramprasad, T.
Copyright Year	2007
Abstract	The occurrence of gas hydrate has been inferred from the presence of Bottom-Simulating Reflectors (BSRs) along the western continental margin of India. In this paper, we assess the spatial and vertical distribution of gas hydrates by analyzing the interval velocities and Amplitude Versus Offset (AVO) responses obtained from multi-channel seismics (MCSs). The hydrate cements the grains of the host sediment, thereby increasing its velocity, whereas the free gas below the base of hydrate stability zone decreases the interval velocity. Conventionally, velocities are obtained from the semblance analysis on the Common Mid-Point (CMP) gathers. Here, we used wave-equation datuming to remove the effect of the water column before the velocity analysis. We show that the interval velocities obtained in this fashion are more stable than those computed from the conventional semblance analysis. The initial velocity model thus obtained is updated using the tomographic velocity analysis to account for lateral heterogeneity. The resultant interval velocity model shows large lateral velocity variations in the hydrate layer and some low velocity zones associated with free gas at the location of structural traps. The reflection from the base of the gas layer is also visible in the stacked seismic data. Vertical variation in hydrate distribution is assessed by analyzing the AVO response at selected locations. AVO analysis is carried out after applying true amplitude processing. The average amplitudes of BSRs are almost constant with offset, suggesting a fluid expulsion model for hydrate formation. In such a model, the hydrate concentrations are gradational with maxima occurring at the base of hydrate stability zone.
Starting Page	201
Ending Page	211
Page Count	11
File Format	PDF
ISSN	00253235
Journal	Marine Geophysical Researches
Volume Number	28
Issue Number	3
e-ISSN	15730581
Language	English
Publisher	Springer Netherlands
Publisher Date	2007-07-20
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Gas hydrates BSRs Velocity analysis AVO analysis Wave-equation datuming Error analysis Tomographic velocity analysis Offshore Engineering Geosciences Geophysics/Geodesy Oceanography
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology Geophysics Oceanography

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