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Book Chapter

Effects of Methane Hydrate on the Physical Properties of Sediments

By
William J. Winters
William J. Winters
U.S. Geological Survey, Woods Hole, Massachusetts, U.S.A.
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William F. Waite
William F. Waite
U.S. Geological Survey, Woods Hole, Massachusetts, U.S.A.
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David H. Mason
David H. Mason
U.S. Geological Survey, Woods Hole, Massachusetts, U.S.A.
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Published:
January 01, 2009

Abstract

Grain size, pore content, and arrangement of pore constituents have a profound effect on acoustic and strength properties of sediments. We tested specimens containing gas hydrate, methane, and water in the pore space of coarse- and fine-grained sediments to simulate the marine environment and of frozen coarse-grained sediment to simulate permafrost conditions.

The measured compressional wave velocity (Vp) changes with the extent to which the pore material cements sediment grains. Hence, for equal effective stresses, Vp is lowest in gas-charged sediments, increases for water-saturated sediments, then increases significantly for hydrate-bearing sediments because of sediment cementation provided by hydrate. Frozen sediment, effectively fully saturated and fully cemented sediment, exhibits the highest Vp.

Sediment strength follows the same pattern but also shows a strong dependence on sediment grain size. For consolidation stresses associated with the upper several hundred meters of subbottom depth, pore pressures decreased during shear in coarse-grained sediments containing gas hydrate, thereby increasing strength, whereas pore pressure in fine-grained sediments typically increased during shear, which decreased strength. The presence of free gas in pore space damped the pore-pressure response during shear and reduced the strengthening effect of gas hydrate in sands.

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Contents

AAPG Memoir

Natural Gas Hydrates—Energy Resource Potential and Associated Geologic Hazards

T. Collett
T. Collett
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A. Johnson
A. Johnson
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C. Knapp
C. Knapp
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R. Boswell
R. Boswell
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American Association of Petroleum Geologists
Volume
89
ISBN electronic:
9781629810270
Publication date:
January 01, 2009

GeoRef

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