Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

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2-D Velocity Structure in Kerala-Konkan Basin using Traveltime Inversion of Seismic Data


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1 CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, India
     

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The existence of gas-hydrates in marine sediments increases the seismic velocity, whereas even a small amount of underlying free-gas reduces the velocity considerably. The change in velocities against the background (without gas-hydrates and free-gas) velocity can be used for identification and assessment of gas-hydrates. Traveltime inversion of identifiable reflections from large offset multi channel seismic (MCS) experiment is an effective method to derive the 2-D velocity structure in an area. We apply this method along a seismic line in the Kerala-Konkan (KK) offshore basin for delineating the gas-hydrates and free-gas bearing sediments across a bottom simulating reflector (BSR). The result reveals a four layer 2-D shallow velocity model with the topmost sedimentary layer having velocity of 1,680-1,740 m/s and thickness of 140-190 m. The velocity of the second layer of uniform thickness (110 m) varies from 1,890 to 1,950 m/s. The third layer, exhibiting higher velocity of 2,100-2,180 m/s, is interpreted as the gas-hydrates bearing sediment, the thickness of which is estimated as 100 to 150 m. The underlying sedimentary layer shows a reduction in seismic velocity between 1,620 to 1,720 m/s. This low-velocity layer with 160-200 m thickness may be due to the presence of free-gas below the gas-hydrates layer.

Keywords

Gas-Hydrates, Free-Gas, Velocity, BSR, Traveltime Inversion.
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  • 2-D Velocity Structure in Kerala-Konkan Basin using Traveltime Inversion of Seismic Data

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Authors

Praveen Kumar Singh
CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, India
Kalachand Sain
CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, India

Abstract


The existence of gas-hydrates in marine sediments increases the seismic velocity, whereas even a small amount of underlying free-gas reduces the velocity considerably. The change in velocities against the background (without gas-hydrates and free-gas) velocity can be used for identification and assessment of gas-hydrates. Traveltime inversion of identifiable reflections from large offset multi channel seismic (MCS) experiment is an effective method to derive the 2-D velocity structure in an area. We apply this method along a seismic line in the Kerala-Konkan (KK) offshore basin for delineating the gas-hydrates and free-gas bearing sediments across a bottom simulating reflector (BSR). The result reveals a four layer 2-D shallow velocity model with the topmost sedimentary layer having velocity of 1,680-1,740 m/s and thickness of 140-190 m. The velocity of the second layer of uniform thickness (110 m) varies from 1,890 to 1,950 m/s. The third layer, exhibiting higher velocity of 2,100-2,180 m/s, is interpreted as the gas-hydrates bearing sediment, the thickness of which is estimated as 100 to 150 m. The underlying sedimentary layer shows a reduction in seismic velocity between 1,620 to 1,720 m/s. This low-velocity layer with 160-200 m thickness may be due to the presence of free-gas below the gas-hydrates layer.

Keywords


Gas-Hydrates, Free-Gas, Velocity, BSR, Traveltime Inversion.

References