Abstract: GHASTLI--Gas Hydrate and Sediment Test Laboratory Instrument

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

Methane hydrates exist beneath many continental margins and represent a huge potential alternate energy source. A custom-built laboratory test system is currently being used to study the formation and decomposition of gas hydrates at sea-floor pressures and temperatures and the physical, acoustic, electrical, and chemical properties of hydrate-sediment mixtures. A scanning electron microscope with a liquid-nitrogen cryogenic stage will be used to examine the hydrate crystals and sediment grains. Our goals are to understand interrelationships of natural factors and the formation of gas hydrates in marine sediment. We will also examine hydrate dissociation characteristics and measure sediment properties before, during, and after the formation of hydrates to better understand their influ nce on possible methane extraction.

The test system consists of a fluid-filled vessel that can apply a maximum external pressure of 25 MPa (equivalent to a 2400-m water depth) to a cylindrical sediment specimen. Because internal specimen pore pressure can also be controlled, hundreds of meters of overburden pressure can be applied. A heat exchanger on the upper surface of the test specimen not only allows application of appropriate temperatures, it also creates a unidirectional cooling front downward through the sample at the same time that methane gas is slowly percolated upward to induce hydrate formation.

Hydrate formation can be quantitatively monitored by electrical resistivity sensors placed around the perimeter of the specimen. Acoustic velocity (both P- and S-wave) can also be measured vertically through the sample, as can shear strength, pore pressure, and permeability, all at in-situ conditions.

AAPG Search and Discovery Article #90984©1994 AAPG Annual Convention, East Lansing, Michigan, September 18-20, 1994