Study on Dissociation Behaviors of Methane Hydrate in Porous Media Based on Experiments and Fractional Dimension Shrinking-Core Model

The dissociation kinetics of methane hydrate in the silica gels as the porous media are studied when the temperatures are above the quadruple-phase (hydrate(H)-water(L-W)-ice(I)-vapor(V)) point temperatures. The dissociation experiments were carried out by depressurization in the temperature range of 269.15-278.15 K and the initial formation pressure range of 4.1-11.0 MPa. Four silica gels, with pore sizes of 9.03, 12.95, 17.96, and 33.2 nm (the particle size distribution is 0.105-0.15 mm) were used. The experimental results shows that the rate of methane released from the hydrate dissociation increases with the increase of the initial formation pressure, the decrease of the environmental temperature, and the increase of the pore size. The temperature in the hydrate crystallizer first immediately has an obvious drop in the process of the hydrate dissociation and then rises gradually to the environmental temperature after it reaches the lowest temperature point. Based on the fractal theory and the shrinking-core model, a fractional dimension shrinking-core model is established for the correlation and prediction of the dissociation kinetic behaviors of methane hydrate in the porous media above the corresponding quadruple-phase point temperatures. The results are in good agreement with the experimental data.