Study on the heat recovery behavior of horizontal well systems in the Qiabuqia geothermal area of the Gonghe Basin, China

Geothermal energy, as a highly regarded renewable energy source, holds vast potential for widespread applications. However, the methods of geothermal energy extraction need to be optimized and improved according to specific geological conditions. This study aims to provide a multi-level horizontal branch well heat recovery system for the Qiabuqia geothermal field in the Gonghe Basin. To begin, this study systematically investigated the influence of various engineering parameters on production temperature and establishes mathematical models to depict the relationships among these parameters. Subsequently, we unveiled the precise numerical correlation between well length and the limit injection rate, utilizing multiple production indexes to comprehensively characterize the practical production characteristics and effectiveness of the multi-level heat recovery system. Finally, a comprehensive economic evaluation of the system was conducted. The research findings indicate that there exists a linear relationship between production temperature and injection temperature, while a second-order polynomial relationship is observed between production temperature and injection rate, wellbore size, and well length. In single-well heat recovery systems, the ratio of well length to the limit injection rate is 4000, whereas in multi-level branch well system, the limit injection rate is 88 % of that in single-well systems. Furthermore, branch wells located farther from the injection end exhibit greater heat recovery capacity but relatively higher production costs. Nonetheless, overall, the production cost for 1000-m-long branch wells can be reduced to around $0.05 $/kWh, demonstrating significant economic feasibility. These research findings provide momentum for the sustainable development and utilization of hot dry rock resources, simultaneously offering more precise guidance for the design and operation of hot dry rock power generation projects.