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

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 perme-ability 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 sig-nificant 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.

Automated summary

Permeability is a crucial parameter for evaluating hydrate-bearing sediments (HBS) as reservoirs and for developing exploitation plans. However, previous permeability studies of HBS have not taken into account effective stress and seepage pressure difference, which is inconsistent with the actual stress-seepage coupling process in hydrate exploitation. This study conducted water permeability tests on hydrate-bearing clayey-silty sediments (HBCSS) synthesized using marine clay from the South China Sea and quartz sand, in order to investigate the effects of effective stress, hydrate saturation, and seepage pressure difference on permeability. The experimental results show that effective stress significantly decreases permeability, especially at the beginning of stress increase. Furthermore, the relationship between hydrate saturation and permeability follows a negative exponential pattern due to the blockage mechanism of hydrate particles. The change in effective stress is the main factor influencing permeability in response to seepage pressure difference, with the effect weakening as hydrate cementation increases. Based on these findings, permeability models considering the coupling effect of effective stress and hydrate saturation were proposed.