Triaxial compressive properties of artificial methane-hydrate-bearing sediment

Knowledge of the mechanical properties of gas-hydrate-bearing sediments is essential for simulating the geomechanical response to gas extraction from a gas-hydrate reservoir. In this study, drained triaxial compression tests were conducted on artificial methane-hydrate-bearing sediment samples under hydrate-stable temperature-pressure conditions. Toyoura sand (average particle size: D-50 = 0.230 mm), number 7 silica sand (D-50 = 0.205 mm), and number 8 silica sand (D-50 = 0.130 mm) were used as the skeleton of each specimen. Axial loading was conducted at an axial strain rate of 0.1% min(-1) at a constant temperature of 278 K. The cell and pore pressures were kept constant during axial loading. We found that the strength and stiffness of the hydrate-sand specimens increased with methane hydrate saturation and with the effective confining pressure, and the secant Poisson's ratio decreased with the effective confining pressure. The stiffness depends on the type of sand forming the skeleton of the specimens, although the strength has little dependence on the type of sand. According to an earlier work, hydrate-sand specimens are thought to contract in the early stage of axial loading before starting to expand owing to the dilatancy effect, as is the case for many other geological materials. The test results in this study are discussed in relation to the deformation mechanism proposed in an earlier work.