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Abstract

AAPG Bulletin, V. 106, No. 5 (May 2022), P. 1101-1126.

Copyright ©2022. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/01132221002

Compression behavior of hydrate-bearing sediments

Yi Fang, 1Peter B. Flemings,2 John T. Germaine,3 Hugh Daigle,4 Stephen C. Phillips,5 and Josh O’Connell6

1Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas; present address: Department of Geology and Geological Engineering, South Dakota School of Mines and Technology; [email protected]
2Institute for Geophysics and Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas; [email protected]
3Department of Civil and Environmental Engineering, Tufts University, Medford, Massachusetts; [email protected]
4Hildebrand Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, Austin, Texas; [email protected]
5Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas; present address: US Geological Survey, Woods Hole, Massachusetts, [email protected]
6Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas; [email protected]

ABSTRACT

This work experimentally explores porosity, compressibility, and the ratio of horizontal to vertical Previous HiteffectiveNext Hit stress (K0) in hydrate-bearing sandy silts from Green Canyon Block 955 in the deep-water Gulf of Mexico. The samples have an in situ porosity of 0.38 to 0.40 and a hydrate saturation of more than 80%. The hydrate-bearing sediments are stiffer than the equivalent hydrate-free sediments; the K0 stress ratio is greater for hydrate-bearing sediments relative to the equivalent hydrate-free sediments. The porosity decreases by 0.01 to 0.02 when the hydrate is dissociated at the in situ Previous HiteffectiveTop stress. We interpret that the hydrate in the sediment pores is a viscoelastic material that behaves like a fluid over experimental time scales, yet it cannot escape the sediment skeleton. During compression, the hydrate bears a significant fraction of the applied vertical load and transfers this load laterally, resulting in the apparent increased stiffness and a larger apparent K0 stress ratio. When dissociation occurs, the load carried by the hydrate is transferred to the sediment skeleton, resulting in further compaction and a decrease in the lateral stress. The viewpoint that the hydrate is a trapped viscous phase provides a mechanism for how stiffness and stress ratio (K0) are greater when hydrate is present in the porous media. This study provides insight into the initial stress state of hydrate-bearing reservoirs and the geomechanical evolution of these reservoirs during production.

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