--> ABSTRACT: A Laboratory Facility for Forming and Testing Gas Hydrates in Marine Sediment at In-Situ Conditions, by William J. Winters, James S. Booth, David H. Mason, William P. Dillon, Robert F. Commeau; #91020 (1995).

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A Laboratory Facility for Forming and Testing Gas Hydrates in Marine Sediment at In-Situ Conditions

William J. Winters, James S. Booth, David H. Mason, William P. Dillon, Robert F. Commeau

A computer-controlled custom-built laboratory test system currently is being used to study the formation and dissociation characteristics of gas hydrates in marine sediment at sea floor pressures and temperatures. Evidence suggests that gas hydrates exist at numerous geographic locations beneath continental margins where high hydrostatic pressure coupled with low temperatures in the presence of sufficient quantities of gas (predominantly methane) have caused hydrates to form and remain stable.

We intend to measure physical, acoustic, electrical, and chemical properties of laboratory-formed, hydrate-sediment mixtures and apply this information to the analysis of offshore areas suspected of containing large quantities of gas hydrates. This will provide knowledge to better understand how: (1) hydrates formed in-situ, (2) methane might be extracted, (3) the amount of hydrate can be better quantified from seismic profiles, (4) global climate is affected by methane release, and (5) mass wasting may be influenced by hydrate dissociation.

In-situ hydrostatic pressures (equivalent to a maximum 2500-m water depth; 25 MPa) and temperatures are applied to a 7.1-cm diameter by 14.2-cm high, vertically oriented cylindrical sediment specimen within a silicone-oil-filled chamber. Overburden pressure can be simulated because internal pore pressure is controlled. Furthermore, an adjustable unidirectional cooling front can be induced downward through the sample at the same time that methane gas is slowly percolated upward to induce hydrate formation. Numerous parameters that can be measured and calculated during a test include acoustic velocity, electric resistivity, shear strength, and permeability. We use a scanning electron microscope with a liquid-nitrogen cryogenic stage to examine the crystalline structure of hydrates and t eir relationships with sediment grains. An individual test can include up to 90 different pressure, gas-charging, and temperature segments. To date, tests have approximated 2 weeks in length; however, our future test program includes much longer test intervals.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995