Experimental analysis and numerical simulation study on the influence law of heat transfer in horizontal sections of medium-depth geothermal wells.

Promoting medium- and deep-seated geothermal heating technology is a key initiative for achieving global carbon peak and carbon neutrality goals. The heat transfer system in the mid-depth horizontal well section avoids damage to groundwater and the environment; however, complex nonlinear interactions exist among influencing factors such as flow rate, wellbore length, and diameter. Therefore, this paper proposes a new design concept to investigate the heat transfer laws of horizontal well sections. First, indoor experiments are conducted to evaluate the heat transfer performance of geothermal wells. Second, based on a U-shaped geothermal well in the Guanzhong Basin, Shaanxi Province, China (burial depth: 2050 m), a full-scale numerical model of heat transfer inside and outside the pipeline is constructed using on-site parameters, including inlet temperature and injection flow rate. Through theoretical analysis and numerical calculations, we validate the variations in outlet temperature and heat extraction during the heating period, as well as the formation temperature recovery during the non-heating period. The optimal flow rate and maximum heat extraction that allow the formation to fully restore its original temperature are determined. The results show that a higher flow rate leads to a lower outlet temperature but greater heat extraction over the same heating period. For this specific geothermal well, the optimal flow rate is 0.3 m/s, yielding a maximum heat extraction of 1.81 × 1013 J from the horizontal well section. These findings provide a theoretical basis and design reference for optimizing flow rate and heat extraction in medium-deep geothermal heating systems, ensuring sustainable utilization of geothermal resources.