Methane Hydrates in Porous Layers: Gas Formation and Convection

This is a review of recent analytical and numerical work on the generation and flow of methane gas through a layer of porous medium impregnated with solid clathrate hydrates. The porous layer is depressurized suddenly on its lower plane and the phase-change front advances under the influence of heat conduction and convection. The first part of the chapter describes a simplified analytical solution based on a unidirectional phase-change model in which the conduction in the gas-filled region behind the front is neglected. The chapter continues with numerical results for the evolution of the unidirectional phase-change process. Both methods lead to the conclusion that the rate of gas flow through the depressurized (bottom) plane of the layer decreases approximately as t −1/2. Further numerical modeling shows that the presence of a vertical geothermal gradient has a significant effect on the rate of gas generation. Numerical results for phase change and gas generation in a porous sediment with non-uniform porosity and permeability are also reported.