3D investigation of the effects of multiple-well systems on methane hydrate production in a low-permeability reservoir

The utilization of multiple-well systems was proposed as a novel approach for the future commercial gas production from offshore methane hydrate deposits. In order to investigate their effects on methane hydrate production in a low-permeability reservoir, a 3D reservoir model combined with multiple-well systems was established in this study, and long-term numerical simulations of gas production from methane hydrate reservoirs by depressurization were conducted to reveal the complex phenomena of pressure propagation, heat transfer, and gas-liquid two-phase flow in different production systems through 3D visualization. Furthermore, the hot water injection method was also applied in the multiple-well system to examine its effect on gas recovery enhancement. The numerical analyses indicated that the dual-well system had the best performance in gas recovery in a low-permeability reservoir by depressurization, while with the increase in well number, the gas production potential decreased contrarily. In addition, "blind area effect" was found for the first time, which was likely to occur in a low-permeability reservoir when using multiple-well systems (well number > 2) by depressurization. This phenomenon was essentially caused by secondary hydrate formation in the reservoir, which would result in the free gas accumulation in the center region of the vertical wells and thus the decrease in gas production. The hot water injection method could eliminate the blind area effect by preventing secondary hydrate formation and significantly enhance gas recovery in a low-permeability reservoir when using multiple-well systems.