Simulation of Methane Production from Hydrates by Depressurization and Thermal Stimulation

Recently methane hydrates have attracted attention due to their large quantity on the earth and their potential as a new resource of energy. This paper describes a one-dimensional mathematical model and numerical simulation of methane hydrate dissociation in hydrate reserves by both depressurization and thermal stimulation using a one-dimensional radial flow system (axisymmetric reservoir). A moving front that separates the hydrate reserve into two zones is included in this model. A numerical coordinate transformation method was used to solve the moving boundary problem. The partial differential equations were discretized into ordinary differential equations using the method of lines. Our simulations showed that the moving front location and the gas flow rate production are strong functions of the well pressure and reservoir temperature. The impermeable boundary condition at the reservoir results in very low temperature at the moving front and the formation of ice. The formation of ice, which plugs the pore volume for the gas to flow, should be avoided. Compared with a stationary water phase model, our simulations showed that the assumption of a stationary water phase overpredicts the location of the moving front and the dissociation temperature at the moving front and underpredicts the gas flow rate. The thermal stimulation using constant temperature at the well method using a single well was found to have a limited effect on gas production compared to gas production due to depressurization.