Evaluation of geothermal exploitation using abandoned horizontal wells in Sichuan Basin

The number of abandoned shale gas wells is increasing, and many of these wells contain geothermal resources, offering a cost-effective method for extracting geothermal energy for power generation and heating. Currently, heat extraction research predominantly focuses on single vertical wells in shallow to mid-depth strata, with limited studies on deep abandoned horizontal wells and well platforms. Therefore, abandoned horizontal shale gas wells in the Sichuan Basin were selected as the research subject. A full-scale numerical model of the coaxial deep borehole heat exchanger (CDBHE) system was established, and sensitivity analysis of heat exchanger parameters and the comparison of the alternating production modes among multiple wells were conducted. The results indicate that the system's heat transfer performance improves with increased formation thermal conductivity, and vertical and horizontal cross section depths and decreases with the thermal conductivity of the inner tube. The recommended flow direction of circulating water is from the outer pipe to the inner pipe. Furthermore, optimizing heat recovery through alternating production and shutdown of different well-site groups is recommended. This study demonstrates that while the geothermal production efficiency of a single abandoned shale gas well does not compare to that of traditional geothermal wells, the proximity of numerous abandoned wells offers significant leverage for optimizing production and shut-in coordination to meet energy output needs.