Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Petroleum Science and Engineering 56 (2007): 127-135, doi:10.1016/j.petrol.2006.02.003.
Description:
To improve our understanding of the interaction of methane gas hydrate with host
sediment, we studied: (1) the effects of gas hydrate and ice on acoustic velocity in
different sediment types, (2) effect of different hydrate formation mechanisms on
measured acoustic properties (3) dependence of shear strength on pore space contents,
and (4) pore-pressure effects during undrained shear.
A wide range in acoustic p-wave velocities (Vp) were measured in coarse-grained
sediment for different pore space occupants. Vp ranged from less than 1 km/s for gascharged
sediment to 1.77 - 1.94 km/s for water-saturated sediment, 2.91 - 4.00 km/s for
sediment with varying degrees of hydrate saturation, and 3.88 - 4.33 km/s for frozen
sediment. Vp measured in fine-grained sediment containing gas hydrate was substantially
lower (1.97 km/s). Acoustic models based on measured Vp indicate that hydrate which
formed in high gas flux environments can cement coarse-grained sediment, whereas
hydrate formed from methane dissolved in the pore fluid may not.
The presence of gas hydrate and other solid pore-filling material, such as ice,
increased the sediment shear strength. The magnitude of that increase is related to the
amount of hydrate in the pore space and cementation characteristics between the hydrate
and sediment grains. We have found, that for consolidation stresses associated with the
upper several hundred meters of subbottom depth, pore pressures decreased during shear
in coarse-grained sediment containing gas hydrate, whereas pore pressure in fine-grained
sediment typically increased during shear. The presence of free gas in pore spaces
damped pore pressure response during shear and reduced the strengthening effect of gas
hydrate in sands.
Description:
This
work was supported by the Coastal and Marine Geology, and Energy Programs of the
U.S. Geological Survey and funding was provided by the Gas Hydrate Program of the
U.S. Department of Energy.
Keywords:
Acoustic modeling
;
Acoustic velocity
;
Cementation
;
Gas hydrate
;
Physical properties
;
Shear strength
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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