Silty-clayey host sediments have been widely identified in natural gas hydrate-bearing sediments (HBS). While the effect of clay (montmorillonite, kaolinite, illite, etc.) on the kinetics of CH4 hydrate formation and dissociation is still not clear. The purpose of this study was to evaluate the kinetics of CH4 hydrate formation and dissociation in sodium montmorillonite (Na-MMT) suspensions with mass fractions ranging from 0.1 wt% to 9.0 wt%. The results indicate that Na-MMT can promote nucleation but delay the growth kinetics of CH4 hydrate, as indicated by the shortened induction time and prolonged reaction time. It is worth noting that as the mass fraction increases, the induction time increases while the rate of gas uptake decreases. The morphological analysis was conducted simultaneously. It was discovered that in the presence of montmorillonite, CH4 hydrate forms initially at the gas-liquid interface and grows upward along the reactor surface. Additionally, the clay-hydrate stratification is evident, indicating that water migrates upward and exacerbates the spatial heterogeneity of CH4 hydrate. The anti-seepage effect on the clay-water interface prevents water from seeping into the clay layer during the dissociation process. These findings have significant implications for understanding the occurrence of CH4 hydrate and developing optimized energy recovery strategies in clay-rich sediments.
Keywords CH4 hydrate, montmorillonite clay, formation and dissociation kinetics, gas uptake, hydrate-clay morphology