Abstract: To address the technical challenges associated with enhanced geothermal systems, including hydraulic fracturing stimulation, induced seismicity, and uncertainties in reservoir permeability, this study explores an alternative development pathway with improved environmental compatibility and operational stability, namely the closed-loop geothermal system (CLGS). Through a comparative analysis, the technical advantages of CLGS are systematically clarified. First, the research progress on the mechanical stability and efficient heat extraction modes of CLGS under long-term operation is comprehensively reviewed. Particular emphasis is placed on analyzing the effects of different injection-production parameters on heat extraction performance, and the thermal energy extraction efficiency of various heat production modes is comparatively evaluated. Furthermore, the stability mechanisms of the wellbore under coupled thermo-fluid-solid processes are investigated. The results indicate that, for CLGS, a spiral wellbore configuration can significantly enhance long-term heat exchange capacity, with the average heat exchange per unit wellbore length increased by 23.73% over a 50 a operation period. Intermittent heat extraction markedly improves heat transfer efficiency, resulting in an average thermal output increase of 3.95 kW and a cumulative heat production enhancement of 34.6%. In addition, the injection rate is demonstrated to play a critical regulatory role in the evolution of the heat extraction cycle and the stress disturbance process of the wellbore.

Key words: hot dry rock, wellbore stability, thermal energy extraction methods, enhanced geothermal system, closed-loop geothermal system