Experimental study on the permeability of methane hydrate-bearing sediments during triaxial loading

Abstract

The permeability of methane hydrate (MH)-bearing sediments is closely related to the exploitation efficiency of MH deposits. During the exploitation of MHs, the stress state of hydrate-bearing reservoirs is complex, and stratum deformation may occur simultaneously. Both the change in the stress state and stratum deformation may influence the permeability of hydrate-bearing sediments. In this paper, a series of permeability measurement tests was conducted to study the influence of the effective confining pressure and triaxial compression process on the permeability of MH-bearing samples. The test results indicated that the permeability of hydrate-bearing samples was influenced by the effective confining pressure. With increasing effective confining pressure, the permeability of the pure sand sample gradually decreased. For the hydrate-bearing samples, the permeability was also influenced by the effective confining pressure. When the effective confining pressure reached a specific value, a sharp drop in the permeability of the hydrate-bearing samples occurred. The change in permeability might be caused by the increase in fine hydrate particles in the pore space. Based on the test results, the permeability of the hydrate-bearing samples was influenced by the triaxial compression process. During the shearing process, the permeability greatly increased when the axial strain reached a specific value. This phenomenon might be caused by the formation of a shear band. During the production of hydrates, controlling the change in stress applied to the hydrate particles could possibly promote production. Furthermore, the appearance of shear bands or fissures might also increase production by certain methods, such as the hydraulic fracturing process.