Effect of Overconsolidation on the Permeability of Natural Gas Hydrate-Bearing Sediments during Triaxial Shear and Creep Processes

Owing to the combined effects of erosion, unloading, and cementation processes acting upon seabed hydrate-bearing sediments in the South China Sea, the phenomenon of overconsolidation becomes readily apparent. This phenomenon can affect the permeability characteristics of hydrate-bearing sediments in the South China Sea. In this paper, a series of triaxial shear and creep experiments were carried out to study the effect of overconsolidation ratio on the gas phase permeability of methane hydrate-bearing sediments. The results show that, during overconsolidation, the gas phase permeability reduces after overconsolidation, and permeability and effective confining pressure are exponential function relation. During shear, when the overconsolidation ratio is 1, the permeability decreases first and then increases. When the overconsolidation ratios are 2, 3, and 4, the permeability decreases first and then remains stable. During creep, the permeability decreases first and then remains stable. The rise in overconsolidation ratio leads to an increase in initial volumetric strain and a reduction in total volumetric strain throughout the creep process. The porosity increases as the volumetric strain decreases, and the permeability and porosity are positively correlated. This study has guiding significance to clarify permeability evolution rules of hydrate-bearing sediments during hydrate exploitation under overconsolidation conditions.