Numerical Simulation and Analysis of Water Phase Effect on Methane Hydrate Dissociation by Depressurization

Abstract

The gas hydrate dissociation process is always accompanied by water production and water transfer, which may affect gas generation rate. In this study, in order to analyze the water phase effect in the process of dissociation in porous media, a two-dimensional (2-D) axisymmetric simulator is developed to model methane hydrate dissociation in porous media by depressurization. Mass transport, intrinsic kinetic reaction and energy conservation are included in the governing equations, which are discretized by finite difference method and are solved in the implicit pressure-explicit saturation (IMPES) method. Then, a series of simulations are performed to study the relationship among changes of water saturation, temperature, pressure and hydrate saturation in laboratory-scale methane dissociation by depressurization, water transfer in porous media for different outlet pressure and bath temperature, and the sensitivity analysis to water saturation. These results suggest that the front dissociation interface is wrapped in an area where water saturation is distributed in a gradient. As the water moves, the water phase plays an important role in late stage thermal conduction. Higher water saturation may lead to higher gas generation rate in the late stage. The water-unsaturated condition is also forecasted by the simulator. The implications of the data are discussed in detail.