[Objective] Hot dry rock (HDR) possesses unique advantages of enormous reserves, high operational stability, and excellent long-term sustainability, and has been widely regarded as a critical strategic alternative energy resource by countries worldwide in recent years. Enhanced Geothermal System (EGS) represents the most effective technical means for the efficient development of HDR resources, which consists of two interconnected key processes: the underground thermal energy extraction from geothermal reservoirs and the above-ground energy conversion and power generation. However, most existing studies have investigated the thermal extraction performance of HDR reservoirs and the power generation performance of surface systems independently. This decoupled research paradigm fails to fully capture the mutual interactions and inherent coupling relationships between the two subsystems, making it difficult to accurately characterize the overall operational characteristics and identify the optimal performance improvement directions of EGS. Therefore, this study aims to systematically reveal the coupling mechanism between thermal energy extraction and energy conversion processes in EGS, and to provide a comprehensive theoretical basis for the holistic optimization of EGS systems.

[Methods] In this study, two representative EGS configurations are proposed: the water-based EGS (water-EGS) using water as the heat extraction medium and the carbon dioxide-based EGS (CO2-EGS) using supercritical carbon dioxide (scCO2) as the working fluid. Based on the fundamental theories of reservoir engineering, heat transfer, fluid mechanics, and engineering thermodynamics, integrated numerical optimization models coupling thermal extraction and power generation processes are established for both systems respectively. The developed models fully account for the complex physical processes in underground geothermal reservoirs, including heat conduction, thermal convection, and fluid seepage, as well as the operational characteristics of surface power generation systems, such as the performance of heat exchangers, turbines, and condensers. On this basis, a systematic comparative analysis is conducted through numerical simulations to evaluate the dynamic production capacity at the production wellhead and the dynamic power generation performance of water-EGS and CO2-EGS under identical geological conditions (including reservoir temperature, permeability, and thickness) and meteorological conditions (including ambient temperature and solar radiation intensity).

[Results] The simulation results demonstrate that the supercritical CO2 power generation system exhibits significantly higher thermal energy utilization efficiency, with its maximum value reaching 2.49 times that of the water-Organic Rankine Cycle (ORC) power generation system. However, under the same reservoir temperature and reinjection mass flow rate conditions, the water-ORC power generation system outperforms the scCO2 system in terms of heat extraction power and net electrical output power. This finding clearly indicates that the two EGS configurations possess distinct technical strengths and exhibit complementary advantages in different performance indicators.

[Conclusion] This study establishes a fully coupled numerical simulation framework covering the entire EGS process from underground heat extraction to surface power generation, which effectively overcomes the limitations of traditional decoupled research approaches. The research findings provide important theoretical basis and technical support for the optimal design, performance enhancement, and efficient development of enhanced geothermal systems. Furthermore, the comprehensive comparative analysis of water-EGS and CO₂ -EGS offers valuable reference for the rational selection of heat extraction media in practical HDR development engineering applications, and lays a solid foundation for subsequent long-term operational performance evaluation and economic feasibility analysis of EGS projects.