Mesoscale Modeling of Exploiting Methane Hydrate by CO_2 Replacement in Homogeneous Porous Media

摘要

In this study, the objective is to establish a general mesoscale model for replacement so as to precisely estimate the flux of methane hydrate dissociation and CO_2 hydrate formation in the cage of hydrate. If homogeneous porous media is assumed, porosity (void fraction) of methane hydrate sediment can be obtained from silica packing in experiment. Based on considering the driving force of free energy in dissociation and formation processes, a new modeling of replacement process is established by considering the individual flux of hydrate surface at stable and unstable regions of CH_4 hydrate. At stable CH_4 and CO_2 hydrates region, it provides a simple situation of discussing the recovery process which CO_2 guest particle replaces CH_4 in hydrate due to free energy difference. Here, the formation rate of CO_2 hydrate is dominated by the dissociation rate of CH_4. However, large amount of CH_4 dissociated at the surface of hydrate at unstable region. The formation rate become dominated by the formation flux of CO_2 hydrate itself. In addition, the high-pressure effect of accelerating the guest gas trapped in hydrate is also considered by applying kinetic theory of gases. By applying CFD method and unstructured grid, it is possible to consider momentum, concentration and thermal distributions in non-equilibrium state simultaneously. To compare with experimental results, flux of methane hydrate dissociation at high surface concentration in simulation are consistent with experiment.