3D NUMERICAL EVALUATION OF GAS HYDRATE PRODUCTION PER FORMANCE OF THE DEPRESSURIZATION AND BACKFILLING WITH IN-SITU SUPPLEMENTAL HEAT METHOD

Natural gas hydrate(NGH) is a promising clean alternative energy resource for world in future. Based on the analysis of the challenges in the commercial exploitation, the depressurization and backfilling with in-situ supplemental heat method had been proposed to enhance the gas production of methane hydrate reservoir. In this method, the calcium oxide(CaO) powder is injected into the hydrate reservoir, and the natural gas is exploited by depressurization. The water produced by the decomposition of natural gas hydrate will react with the calcium oxide powder rapidly, which would provide amounts heat for supplement thermal energy of the decomposition of natural gas hydrate. This novel method is evaluated by a numerical simulator based on the finite volume method in this work. A three-dimensional reservoir model was constructed. The simulation results indicate that comparing with the conventional horizontal well method and the horizontal well combined fracturing method, this method has a better production performance. Comparing with the horizontal well combined fracturing method, the cumulative gas production of this method is improved, but the cumulative water production has changed slightly simultaneously. Therefore, the recovery efficiency has been significantly improved. The results of the sensitivity analysis of the equivalent permeability of fractures and the mass of CaO injection show that the increasing effect of fracturing on gas production declines with the improvement of equivalent permeability of fractures. In addition, the greater the amount of injected calcium oxide, the more obvious the effect of increasing production. Increasing the amount of injected calcium oxide only increase the gas production, but not significantly increase the water production. Therefore, theoretically the larger the injection, the higher the gas production efficiency. Simultaneously, the feasibility of this method has been testified in reservoirs with different flow capacity. Herein, the improving effect on low-permeability reservoir is more obviously than other cases. Based on the above conclusions, this work quantitatively verifies the potential value of the depressurization and backfilling with in-situ supplemental heat method from the perspective of the theoretical calculation of the three-dimensional model, which looks forward to providing the reference for following work of hydrate recovery.