Effects of Wellbore Parameters on the Performance of an Open-Loop Geothermal System with Horizontal Well

The open-loop geothermal system with a horizontal well is expected to be a favorable approach to develop geothermal energy from reservoirs through an extended horizontal section. The wellbore design is essential for enhancing the performance of a geothermal system. Nevertheless, research on wellbore parameters for open-loop geothermal systems remains scarce. Hence, a coupled wellbore–fractured reservoir mathematical model is developed and numerically solved using COMSOL Multiphysics 5.6. The target geothermal reservoir is located in Xiongan New Area, China. The temperature distribution in the wellbore is analyzed based on the numerical model. Furthermore, the impacts of wellbore parameters—including the thermal conductivity, thickness, and diameter of the insulated pipe, as well as the injection–production spacing—on production performance are systematically evaluated. Grey relational analysis is further employed to quantify the sensitivity of the wellbore parameters. The results show that the wellbore, particularly the insulated pipe, determines the heat loss of the production fluid, while the fractured reservoir dominates the heat extraction capacity of the injection fluid. Reducing the thermal conductivity of the insulation layer has the most significant effect on decreasing the production temperature and thermal power. The injection–production pressure demonstrates a notable decline as the insulation thickness decreases. Increasing the pipe diameter leads to a non-monotonic trend in the injection–production pressure, which first decreases and then increases. There are critical design thresholds for the thermal conductivity, thickness, and diameter of the insulated pipe. Additionally, expanding the injection–production spacing can effectively delay thermal breakthrough and enhance overall system performance. These findings provide valuable guidance for wellbore design in field applications.