1-D MATHEMATICAL MODELING OF HYDRATE DECOMPOSITION IN POROUS MEDIA BY DEPRESSURIZATION AND THERMAL STIMULATION

This paper describes a one-dimensional numerical model for natural gas production from the dissociation of methane hydrate in a hydrate-capped gas reservoir under depressurization and thermal stimulation. The mathematical equations that can describe this type of reservoir include mass balance, heat balance, and kinetics of hydrate decomposition. These nonlinear partial differential equations are solved using the finite-difference fully implicit scheme to obtain the distribution of pressure and saturation of gas, water, and hydrate in the reservoir. In addition, the effect of convection and conduction heat transfer, variation change of formation porosity, the effect of using different equations of state [Peng-Robinson (PR) and modified Esmaeilzadeh-Roshanfekr (ER) equations of state (EOS)], variation change of thermal conductivity of rock, and the effect of using different fluids for thermal stimulation including steam, hot methane, and hot water injection are considered. For thermal stimulation, nine different cases are considered. The results of calculations show that the gas production rate is a sensitive function of well pressure and temperature, and the flow rate of the injected fluid. The results of the model are compared with those of the numerical models of Holder et al. (1982), Moridis (2002), and the HYDRSIM simulator. The results of the proposed model are in good agreement with those of the HYDRSIM simulator.