Optimization of Depressurization and Injection Pressures for Safe and Sustainable Gas Recovery from Hydrate Reservoirs

Abstract

This paper presents the strategy and results of an optimization study performed on a Berea sandstone methane hydrate reservoir subjected to depressurization and simultaneous sequestration mode of gas recovery. The numerical simulations of multi-phase flow and heat transfer prevailing in the reservoir is performed using an in-house hydrate dissociation simulator. The simulator results are utilized to perform a dedicated study on net reservoir volume change due to continuous gas recovery and injection. A list of parameters governing the methane production and reservoir volume change are studied. The results indicate that the injection cycle has a minimal effect on gas production and reservoir volume change. However, both these outcomes depend strongly on the operating pressures of the process. For any hydrate reservoir, changing the operating pressures to increase methane production also increases the reservoir volume change i.e., not a single choice of depressurization and injection pressures exists, which would result in maximum gas production and minimum reservoir volume change. For such a multi-criteria optimization problem, a fuzzy logic method is used to determine the optimum operating point for the present reservoir, which results in a best trade-off between the depressurization and injection pressure.