Experimental Study on the Permeability of Hydrate-Bearing Silty-Clayey Sediments with Grain-Cementing and Pore-Filling Hydrate Morphologies

The permeability of marine hydrate reservoirs is crucial to the gas recovery rate and continuity during long-term hydrate production. Hydrate morphology is a vital permeability-related factor in the pore and field scale, including two typical forms represented by grain-cementing and pore-filling morphologies. Investigating the effect of these two hydrate morphologies on the permeability behaviors of silty-clayey sediments could provide theoretical support for silty-clayey hydrate reservoir development. To this end, hydrates in grain-cementing and pore-filling morphologies were prepared in the laboratory, and a multitude of permeability tests were conducted on hydrate-bearing silty-clayey sediments (HBSCSs) in water-saturated environments containing different hydrate saturations and hydrate morphologies based on a bespoke permeability test apparatus. It is deduced that the hydrate formation and fine migration are key contributors to the decreased effective permeability and enhanced non-Darcy features in silty-clayey sediments, whereas hydrate dissociation would expand the pore space and increase the permeability of sediments. As fine migration stabilizes, the effective permeability of pore-filling HBSCSs increases from 3.5 to 58.8 (10(-3) mD), while grain-cementing HBSCSs experience a decrease from 6.5 to 2.6 (10(-3) mD), with hydrate saturation rising from similar to 10 to similar to 40%. The pore-filling hydrate exerts a stronger blocking mechanism in silty-clayey sediments compared to the grain-cementing hydrate, and this mechanism tends to weaken as the hydrate saturation increases further.