Investigation on the coupling effects of mass transfer limitation and the presence of ice on methane hydrate dissociation inside pore

The exploitation of natural gas hydrates has bottlenecks such as low gas production efficiency and poor sustainability. The scientific issues behind this bottleneck are the continuous mass transfer of methane in the water and the presence of ice phase. A model is proposed to investigate the characteristics of mass transfer limitation and ice formation/melting during methane hydrate dissociation and their effects on hydrate dissociation. A numerical simulation has been carried out on the experimental research, and the reliability of proposed model has been validated by comparing with the experiment data, and consistent results have been obtained. Cumulative methane generation, methane generation rate and volume fraction of phases at local location, distribution of pressure, temperature and phases inside pore were clarified. The findings showed that the dissociation of methane hydrate is very complicated in the presence of the ice phase, and the effect of mass transfer limitation on the hydrate dissociation has become more complicated. These two factors have a great impact on the dissociation rate of methane hydrate. The original pressure and temperature distribution changes due to the ice formation/melting, resulting in the difference in the pressure and temperature at the inner and outer layer inside the pore. Ice formation in the inner layer weakens the delaying and limiting effect of mass transfer limitation on the hydrate dissociation, and ice melting in the outer layer promotes the delaying and limiting effect of mass transfer limitation on the dissociation of the hydrate. The presence of the ice phase weakens the mass transfer limitation effect.