Abstract
In order to solve the low recharge efficiency of middle and deep geothermal Wells, a thermo-hydro-mechanical (THM) model integrating geothermal production and reinjection was established, and the relationship model between recharge efficiency and production well temperature was built to obtain the optimal recharge efficiency. In view of the different well spacing between reinjection and production wells, the different well spacing between production wells and different reinjection well types, numerical simulation and comparative analysis were carried out under the optimal recharge efficiency. The results show that under the optimal recharge efficiency, the change in well spacing has the greatest impact on the exploitation of production wells. The well spacing of production wells is gradually reduced from 600 m to 20 m, and the time of thermal breakthrough in production wells is getting earlier and earlier. However, when the spacing between the production wells reach 200 m, thermal breakthrough hardly occurs. Compared with different well spacings, different reinjection well types have less impact on the exploitation of production wells, and the situation of production wells under one reinjection and two productions is better than one reinjection and one production. Therefore, it is proposed that under the optimal recharge efficiency of 40.41%~72.52%, it is most suitable to use one reinjection and two production, the well spacing between the reinjection and production well above 400 m and the well spacing between the production wells above 200 m and the reinjection wells are horizontal wells is optimal are the most suitable for geothermal exploitation.
Highlights
In recent years, the decrease of traditional fossil energy storage and the environmental pollution that accompanies it has attracted widespread attention
The fitting equation between the recharge efficiency and the temperature change of the production well was established by COMSOL, and an optimal recharge efficiency was obtained
The optimal recharge efficiency is determined for different well spacings between reinjection and production wells, different well types, and production well layout methods
Summary
The decrease of traditional fossil energy storage and the environmental pollution that accompanies it has attracted widespread attention. The harmful substances produced by these traditional energy consumption processes are far more serious than expected (Mei et al, 2018; Shen et al, 2016; Kong et al, 2017). Some problems may occur such as sand-carrying sand production and low recharge efficiency (Sedghi and Zhan, 2020). It is, necessary to study optimized designs for reinjection wells to improve the recharge efficiency of sandstone geothermal reservoirs. Reinjection is an effective protective measure: first, it can effectively treat the wastewater produced by geothermal heat, and to a certain extent, can avoid thermal pollution or pollution to the environment; second, it can help the geothermal reservoir to recover heat production and effectively improve the utilization rate of geothermal resources; third, it can maintain the pressure of geothermal reservoirs, effectively stabilizing the mining conditions of geothermal resources, and preventing ground subsidence (Liu, 2003)
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