27 research outputs found
Methane gas hydrate effect on sediment acoustic and strength properties
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.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.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
Recommended from our members
Physical property changes in hydrate-bearing sediment due to depressurization and subsequent repressurization
Recommended from our members
Physical property changes in hydrate-bearing sediment due to depressurization and subsequent repressurization
PHYSICAL PROPERTIES OF REPRESSURIZED SAMPLES RECOVERED DURING THE 2006 NATIONAL GAS HYDRATE PROGRAM EXPEDITION OFFSHORE INDIA
As part of an international cooperative research program, the U.S. Geological Survey (USGS) and
researchers from the National Gas Hydrate Program (NGHP) of India are studying the physical
properties of sediment recovered during the NGHP-01 cruise conducted offshore India during
2006. Here we report on index property, acoustic velocity, and triaxial shear test results for
samples recovered from the Krishna-Godavari Basin. In addition, we discuss the effects of sample
storage temperature, handling, and change in structure of fine-grained sediment.
Although complex, sub-vertical planar gas-hydrate structures were observed in the silty clay to
clayey silt samples prior to entering the Gas Hydrate And Sediment Test Laboratory Instrument
(GHASTLI), the samples yielded little gas post test. This suggests most, if not all, gas hydrate
dissociated during sample transfer. Mechanical properties of hydrate-bearing marine sediment are
best measured by avoiding sample depressurization. By contrast, mechanical properties of
hydrate-free sediments, that are shipped and stored at atmospheric pressure can be approximated
by consolidating core material to the original in situ effective stress.Non UBCUnreviewe
SEEDING HYDRATE FORMATION IN WATER-SATURATED SAND WITH DISSOLVED-PHASE METHANE OBTAINED FROM HYDRATE DISSOLUTION: A PROGRESS REPORT
An isobaric flow loop added to the Gas Hydrate And Sediment Test Laboratory Instrument
(GHASTLI) is being investigated as a means of rapidly forming methane hydrate in watersaturated
sand from methane dissolved in water. Water circulates through a relatively warm
source chamber, dissolving granular methane hydrate that was pre-made from seed ice, then enters
a colder hydrate growth chamber where hydrate can precipitate in a water-saturated sand
pack. Hydrate dissolution in the source chamber imparts a known methane concentration to the
circulating water, and hydrate particles from the source chamber entrained in the circulating water
can become nucleation sites to hasten the onset of hydrate formation in the growth chamber. Initial
results suggest hydrate grows rapidly near the growth chamber inlet. Techniques for establishing
homogeneous hydrate formation throughout the sand pack are being developed.Non UBCUnreviewe