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

Abstract

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 permeabilityrelated 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 porefilling 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 ∼10 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.