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ABSTRACT: Gas Hydrate Influence on Deepwater Slope Stability

W. A. Dunlap, James R. Hooper

Solid ice-gas compounds called "gas hydrates" occur in deep ocean sediments around the world. It is known that when they melt, the solid ice converts to gas and water. If this happens in slope sediments, landslides might result. A study of relationships between slope stability and gas hydrates shows that there are many ways in which changes in the geologic environment may cause gas hydrates to melt. One example is sea level lowering of the magnitude experienced during the Pleistocene; the pressure decrease reduces the stability of the hydrate. Another is warming of hydrates by increased geothermal heat flow associated with the growth of salt diapirs beneath the region. Geologic changes such as these were modeled using classical 1-D heat flow theory. Typical values for sed ment and hydrate properties were used in a variety of potential geologic and environmental conditions that characterize some continental slope regions. Emphasis was given to interactions between the rate of geologic change and the rate of hydrate melt within the sediment. The latter is controlled by thermal properties of the sediment (resistivity and heat capacity) and hydrates (particularly the latent heat). An additional factor was the rate of change of excess pore water pressures in the sediment in reaction to the expansion of melting hydrate. The results show that the dynamic interactions between these phenomena are equally as important to slope stability as the size of the hypothesized geologic change or the regional slope gradient. Other crucial factors include the water depth, the origin of the hydrate from biologic or reservoir sources, and the strength of the sediment.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990