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Elastic properties of hydrate-bearing sediments using effective medium theory

Elastic properties of hydrate-bearing sediments using effective medium theory
Elastic properties of hydrate-bearing sediments using effective medium theory
Accurate and detailed models of the seismic velocity structure of gas hydrate-bearing sediments may be determined by careful analysis of controlled source seismic data. However, interpretation of these velocities in terms of hydrate saturation of the pore space has hitherto relied on semiempirical formulas and/or simple effective medium theory. We develop a rigorous theoretical scheme to relate the seismic properties of a clay-rich hydrate-bearing sediment to its porosity, mineralogy, microstructural features and hydrate saturation. We consider separately the two possible end-members for the distribution of hydrate in the pore space: (1) hydrates are unconnected and located in the pore voids without appreciable grain contact and (2) connected hydrates are forming cement binding around the grains. The scheme is transversely isotropic, to allow for anisotropy due to alignment of clay platelets, and is based on a combination of a self-consistent approximation, a differential effective medium theory, and a method of smoothing for crystalline aggregates. We have applied the scheme to lithological and seismic velocity data from Ocean Drilling Program Site 995 on the Blake Ridge (southeastern U.S. continental margin) to make estimates of the hydrate saturation. It was found that the hydrates are probably unconnected, and their volume concentration varies between approx. 0% at 100 m below the seabed and approx. 9% at 400 m depth, just above the “bottom simulating reflector”, if the clay platelet orientation distribution resembles the function we have used.
0148-0227
561-577
Jakobsen, M.
0fe8ada8-77b4-41b7-ba68-039200ed3fb1
Hudson, J.A.
f00141cb-a109-4c5e-8be6-ffe21937ad06
Minshull, T.A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Singh, S.C.
b23f1231-1b5d-4843-8b12-0d32fc7bc2c1
Jakobsen, M.
0fe8ada8-77b4-41b7-ba68-039200ed3fb1
Hudson, J.A.
f00141cb-a109-4c5e-8be6-ffe21937ad06
Minshull, T.A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Singh, S.C.
b23f1231-1b5d-4843-8b12-0d32fc7bc2c1

Jakobsen, M., Hudson, J.A., Minshull, T.A. and Singh, S.C. (2000) Elastic properties of hydrate-bearing sediments using effective medium theory. Journal of Geophysical Research, 105 (B1), 561-577. (doi:10.1029/1999JB900190).

Record type: Article

Abstract

Accurate and detailed models of the seismic velocity structure of gas hydrate-bearing sediments may be determined by careful analysis of controlled source seismic data. However, interpretation of these velocities in terms of hydrate saturation of the pore space has hitherto relied on semiempirical formulas and/or simple effective medium theory. We develop a rigorous theoretical scheme to relate the seismic properties of a clay-rich hydrate-bearing sediment to its porosity, mineralogy, microstructural features and hydrate saturation. We consider separately the two possible end-members for the distribution of hydrate in the pore space: (1) hydrates are unconnected and located in the pore voids without appreciable grain contact and (2) connected hydrates are forming cement binding around the grains. The scheme is transversely isotropic, to allow for anisotropy due to alignment of clay platelets, and is based on a combination of a self-consistent approximation, a differential effective medium theory, and a method of smoothing for crystalline aggregates. We have applied the scheme to lithological and seismic velocity data from Ocean Drilling Program Site 995 on the Blake Ridge (southeastern U.S. continental margin) to make estimates of the hydrate saturation. It was found that the hydrates are probably unconnected, and their volume concentration varies between approx. 0% at 100 m below the seabed and approx. 9% at 400 m depth, just above the “bottom simulating reflector”, if the clay platelet orientation distribution resembles the function we have used.

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More information

Published date: 2000

Identifiers

Local EPrints ID: 1282
URI: https://eprints.soton.ac.uk/id/eprint/1282
ISSN: 0148-0227
PURE UUID: fccc8e67-86c5-4525-b287-141e1cbe08d7
ORCID for T.A. Minshull: ORCID iD orcid.org/0000-0002-8202-1379

Catalogue record

Date deposited: 14 Apr 2004
Last modified: 06 Jun 2018 12:52

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