Experimental investigation into gas production from methane hydrate in sediments with different contents of illite clay by depressurization

Natural gas hydrates are widely distributed in silty-clayey sediments, that occur largely in a highly dispersed state. However, the characteristics of the gas production behavior from methane hydrate in silty-clayey sediments are not as comprehensively understood than those in sandy sediments. In this study, a series of experiments employing single-stage depressurization method were conducted to dissociate methane hydrates in silty-clayey sediments with mass fractions of illite ranging from 0 to 50 wt%. The depressurization results indicate that for a high illite content (40 wt% and 50 wt%), the dissociation rate of methane hydrate is dramatically reduced by 33–38% compared to sandy sediments. The lower heat transfer rate in the high-illite-content system caused by the reduced heat conduction of the sediment and more dispersed hydrate distribution results in the lower hydrate dissociation rate. The electrical resistance changes of sediments also indicated that the distribution of hydrate displays a certain degree of heterogeneity, which will cause the resistance changes in sandy sediment more significant than that in silty-clayey sediments. The results are great significant for understanding the gas production behavior of silty-clayey hydrate-bearing sediments and helpful in optimizing methane hydrate exploitation from this specific type of sediment.