Experimental investigation on the permeability characteristics of methane hydrate-bearing clayey-silty sediments considering various factors

Abstract

Permeability is a key physical parameter of hydrate-bearing sediments (HBS), which is an important basis for evaluating reservoirs and developing exploitation plans. However, few permeability studies of HBS conducted so far have involved effective stress and seepage pressure difference, which is inconsistent with the stress-seepage coupling process in actual hydrate exploitation. In this study, marine clay taken from the South China Sea and quartz sand were used to synthesize hydrate-bearing clayey-silty sediments (HBCSS). A series of water permeability tests were conducted to investigate the effects of effective stress, hydrate saturation and seepage pressure difference on the permeability of HBCSS. The results show that an increase in effective stress can cause a significant decrease in permeability, and this effect is particularly pronounced at the beginning of stress increase. The decreasing effective stress can only cause a slight rebound in permeability, as only part of the elastic strain can be recovered. The negative exponential relationship between hydrate saturation and permeability is controlled by the blockage mechanism of hydrate particles. The change in effective stress is the essence of the effect of seepage pressure difference on permeability, and this effect is attenuated with increasing hydrate cementation. Based on the experimental results, permeability models considering the coupling effect of effective stress and hydrate saturation are proposed.