Effective medium modeling to assess gas hydrate and free-gas evident from the velocity structure in the Makran accretionary prism, offshore Pakistan |
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| Authors: | Ranjana Ghosh Kalachand Sain |
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| Institution: | (1) National Geophysical Research Institute (Council of Scientific and Industrial Research), Uppal Road, Hyderabad, 500606, India |
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| Abstract: | Seismic properties of sediments are strongly influenced by pore fluids. Stiffness of unconsolidated marine sediment increases
with the presence of gas hydrate and decreases with the presence of gas. A strong bottom-simulating reflector (BSR) observed
on a seismic profile in the Makran accretionary prism, offshore Pakistan, indicates the presence of gas hydrate and free-gas
across the BSR. Elastic properties of gas depend largely on pressure and temperature. We, therefore, first determine the elastic
modulus of gas at pressure and temperature calculated at the BSR depth in the study region. The interval velocities derived
from the seismic data are interpreted by the effective medium theory, which is a combination of self-consistent approximation
and differential effective medium theories, together with a smoothing approximation, for assessment of gas hydrate and free-gas.
The results show the saturations of gas hydrate and free-gas as 22 and 2.4% of pore space, respectively, across the BSR. |
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| Keywords: | Gas hydrate Elastic property EMT Interval velocity Makran offshore |
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