Compression and Deformation Characteristics of Hydrate-Bearing Sediments under High Effective Confining Pressure

Abstract

The depressurization method that is used to produce methane gas can increase the effective stress in hydrate-bearing sediments and induce deformation and settlement of reservoirs, which has adverse effects on safe and stable exploitation. A series of isotropic consolidation and depressurization dissociation tests under high effective confining pressures on methane hydrate-bearing specimens were conducted to investigate compressive characteristics and deformation behaviors. Isoconsolidation test results demonstrated that the rise in effective confining pressure-induced increasing compressibility and particle crushing of sediment, while the presence of hydrates can suppress compressibility and crushing. The compression index tends to increase with increasing effective stress but decrease with increasing hydrate saturation. Dissociation test results suggested that higher effective stress during dissociation and higher deviatoric stress led to more significant deformation and particle breakage. A specimen can exhibit serious deformation (ɛv ≈ 20%) after dissociation when the effective stress is extremely high (17 MPa), even if the stress state is in the stable zone. During water recovery after dissociation, axial and volumetric strains may further increase under the combined effect of deviatoric stress and high effective confining pressure.