Laboratory testing of clayey-silty hydrate reservoir exploitation: Considering the permeability-stress coupling effect

Abstract

Elucidating the multi-field, multi-phase coupling mechanisms in submarine hydrate reservoirs is essential for releasing their energy potential. Current research gaps remain in understanding the permeability-stress coupling characteristics of hydrate reservoirs. This study conducted permeability-stress coupling tests on hydrate-bearing clayey-silty sediments (HBCS). The seepage characteristics and mechanical response of HBCS under seepage-stress coupling effects were investigated. The results indicate that under stress conditions, the seepage flow of HBCS follows a logarithmic relationship with axial strain, with its rate of increase decelerating as axial strain grows. Apparent permeability decreases rapidly at first and then more gradually with increasing axial strain. Hydrate saturation (S_h) and seepage pressure difference (P_S) exhibit a coupling effect on apparent permeability. At low-S_h levels, particle migration induced by seepage reduces permeability. At high-S_h levels, permeability is affected by two competing mechanisms (pore expansion and particle migration) driven by seepage forces. Unlike triaxial tests for HBCS, under seepage conditions, the plastic deformation capacity of HBCS is enhanced. The stress-strain curve exhibits strain hardening and plastic flow, and lacks obvious strain softening. Shear strength decreases with increasing S_h and P_S, while the secant modulus E₅₀ rises with both parameters. During hydrate exploitation, production efficiency correlates with S_h. In low-S_h reservoirs, a “slow and steady” production strategy is recommended to prevent sand production and wellbore blockage. In high-S_h reservoirs, increasing P_S can promote pore expansion and fracture propagation, thereby enhancing production efficiency. This study provides a reference for engineers to understand the multi-field and multi-phase coupling characteristics during the exploitation of hydrate reservoirs.