Pore-network study of methane hydrate dissociation.

A two-dimensional pore-network model based on invasion percolation is used to study the patterns obtained from the release of methane during the dissociation of methane hydrates (without including dissociation kinetics) caused by a sudden pressure reduction in the system below the hydrate equilibrium pressure. The concept of the critical gas saturation S(gc) (volume fraction of the gas phase at the onset of bulk gas flow) is introduced to analyze gas hydrate dissociation. The effects of throat-size distribution (corresponding to off-shore oceanic sediments or on-shore sediments under permafrost), applied pressure difference across the network, and initial hydrate saturation on the resulting gas patterns and on the critical gas saturation are examined to determine the possibility of producing methane. As expected, large throat sizes or wide throat distributions, large pressure drops, and higher initial hydrate saturation act as promoters for the production of the released gas. For typical deep ocean sediments with small pore sizes and low hydrate saturation, it may be difficult to produce methane resulting from hydrate dissociation.