Numerical Simulation of the Gas Production Behavior of Hydrate Dissociation by Depressurization in Hydrate-Bearing Porous Medium

To evaluate the potential for the commercially viable production of gas from hydrate reservoirs, several pieces of key information are needed to examine in hydrate dissociation process in porous media. In this study, a two dimensional (2D) axisymmetric finite-difference, fully implicit model was developed to investigate the gas production behavior of hydrate dissociation by depressurization in hydrate-bearing porous media. The simulation results indicated that the hydrates dissociate along the radial and longitudinal direction, and the dissociation in the radial direction is earlier than that of the longitudinal direction of the laboratory-scale hydrate sample. Moreover, a series of simulations was performed to study the effect of several parameters including initial hydrate saturation, permeability reduction index N, absolute/relative permeability, intrinsic porosity, and the assumption of stationary water phase on the gas production behavior from hydrate dissociation in hydrate-bearing porous media. The results of the sensitivity analysis showed that significant amelioration of gas production behavior is obtained with high initial hydrate saturation, low permeability reduction index, high gas relative permeability, and high intrinsic porosity. On the other hand, it can be found that the cumulative gas production is not affected by the absolute permeability and the assumption of stationary water phase with the condition of simulation scale length vs diameter L/d < 50; however, there would be some opposite results presented in gas production performance under a larger simulation scale L/d > 50. Finally, the simulation results also suggested that the reliable relative permeability model and the reasonable value of the permeability reduction index corresponding to different forms of hydrate occupying in the porous media should be very important to predict the gas production performance from hydrate dissociation by depressurization and improve the accuracy of numerical simulator.