Triaxial compression of hydrate-bearing sediments undergoing hydrate dissociation by depressurization

This experimental study investigates the geomechanical stability of methane hydrate-bearing sediments (MHBS) during hydrate dissociation. Two MHBS specimens were prepared using sand and 5 wt% clay mixtures, and both with a targeted hydrate saturation of ∼40%. The two specimens were initially subjected to two different deviator stresses, i.e., one below the strength of host sediment (stable) and the other above that but below the strength of the hydrate-bearing sediment (metastable). After the initial shearing, a sequential process of depressurization, re-pressurization (pore pressure recovery), and re-shearing was conducted. During the tests, stress, strain, and hydrate saturation were continuously measured, together with P- and S-wave velocities at each critical step of the tests. Experimental results showed that during hydrate dissociation via depressurization, the specimens underwent volumetric contractions. During the re-pressurization, however, the specimen under a higher initial deviator stress (i.e., under metastable state) failed, whereas the other specimen under a lower initial deviator stress (i.e., under stable state) remained stable. The specimen under the stable state, seemingly having a small amount of reformed hydrates after the re-pressurization, was able to sustain the re-shearing up to a shear stress that is comparable to the shear strength of its host sediment. •Studied are mechanical responses of hydrate-bearing sediments to depressurization.•P- and S-wave velocities are measured at each experimental step.•Discussed is the impact of hydrate dissociation on the sediment stability.