Gas production from muddy hydrate reservoirs by a spiral multilateral well network: Effects of well deployment and production methods

Abstract

Spiral multilateral well networks are expected to enhance the production efficiency of muddy hydrate reservoirs substantially. However, the optimal well-network parameters and production strategy remain unknown, as does the law of synergistic production. Therefore, this study aimed to evaluate the effects of well number, deployment orientation, and production methods of spiral multilateral wells on gas production from ultralow-permeability (<1 mD) and low-permeability (1–100 mD) muddy hydrate reservoirs. The law of synergistic production of multiple wells and the evolution of production overlap zones were revealed. The results show that increasing the number of spiral multilateral wells improves gas recovery from different muddy hydrate reservoirs. However, the change in deployment orientation of spiral multilateral wells has less impact on production performance. Synergistic depressurization of multiple spiral multilateral wells enhances gas recovery, decreases water production, and eliminates gas production in the “blind zone”, effectively avoiding the limitations of multiple vertical wells. Synergistic effects (i.e., two spiral multilateral wells are more productive than twice the production efficiency of one) persist in muddy hydrate reservoirs with ultralow-permeability, enhancing gas production. Contrary to popular assumption, the single depressurization method is more effective than the depressurization and thermal co-stimulation methods, particularly for the long-term production of ultralow-permeability hydrate reservoirs and short-term production of low-permeability hydrate reservoirs. These findings are critical for significantly enhancing gas production from muddy hydrate reservoirs using spiral multilateral wells.