Optimization of energy efficiency in gas production from hydrates assisted by geothermal energy enriched in the deep gas

•Enhancing the hydrate production efficiency by utilizing the geothermal energy carried by the deep gas was studied.•Uncontrollable deep gas injection could inhibit the hydrate dissociation.•Deploying the dual production wells with a long crossflow distance effectively promoted gas diffusion and injected energy utilization.•Determining the suitable depressurization rate and crossflow distance was more crucial than varying the production wells. Scaled-up production from natural gas hydrates is still facing the significant issues of limited gas yield and unsustainable hydrate dissociation. In this work, the deep gas with huge reserves and abundant geothermal energy was used to enhance the hydrate production efficiency. Results showed that the geotherm-assisted gas production was significantly increased by 178.22 %. Surprisingly, the hydrate dissociation rate was slightly weakened by 3.66 % due to the hindered fugacity of the gas from hydrate decomposition as a result of the fast deep gas upwelling. Besides, the energy flow analysis showed that up to 40.67 % of the deep gas injection energy was dissipated to the surroundings, with only 8.28 % utilized for the hydrate decomposition. Consequently, the multi-well deployment was used to regulate the deep gas injection rate. It was found that the multiple wells weakened the sealing effect of hydrate on migration channels, preventing the violent gas upwelling while increasing the hydrate decomposition amount under geothermal stimulation. Then, prolonging crossflow distance of deep gas in the hydrate layer enabled the sediment to absorb more injected energy, resulting in the minimum wasted energy ratio. Not limited to this, the more stable gas production throughout the whole process effectively guaranteed the safety of exploitation. Finally, the hydrate decomposition rate in the depressurization and constant pressure stages was found to be positively correlated with the utilization ratio of the injected energy and the injected rate, respectively. The results could help guide the formulation of the multi-gas joint production scenarios in the field tests to balance production efficiency and cost.