Stern, Laura1, William Durham2, Stephen Kirby1, Sue
Circone1, Mike Helgerud3
(1) U.S. Geological Survey, Menlo Park, CA
(2) UC Lawrence Livermore National Laboratory, Livermore, CA
(3) ExxonMobil, Houston,
ABSTRACT: Experimental Observations Pertinent to the Mechanical and Thermal Stability of sI Methane Hydrate/Sand Aggregates
Several observations suggest that hydrocarbon clathrate hydrates are strong and hence can serve to increase the strength and cohesion of sediments.:(1) Numerous hydrostatic and uniaxial compaction experiments on pure, gas-saturated porous hydrate indicate that effective pressures approaching 100 MPa are required to fully compact sI methane hydrate and sII methane-ethane hydrate. This compares with effective compaction pressures of less than 1 MPa for the compaction of granular ice near its melting temperature. (2) Hydrate/sand aggregates synthesized by the ice-to-hydrate method are found to be more cohesive and durable that comparable ice/sand aggregates. This observation is consistent with experience in drill coring of hydrate/sand intervals compared with that in permafrost. (3) Triaxial compression tests indicate that sI methane hydrate and sII methane-ethane hydrate have ductile flow strengths that are 20 to 100 times stronger than ice under the same conditions, suggesting that their effects in increasing the strength of sediments may be larger than the effect of ice formation in arctic soils in producing permafrost. These results suggest that hydrates may have similar roles as the diagenetic minerals quartz and carbonates during lithogenesis. Such strengthening effects of hydrates in sediments should be lost during thermal decomposition. This weakening effect of hydrate decomposition is in addition to the pore-pressure effect of gas release. Hydrate decomposition is endothermic and rate controlled by heat flow at temperatures above above 0 °C. These properties place severe limits on the conditions under which decomposition may be thermally and mechanically unstable.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.