Flow and Heat Transfer of Supercritical CO2 in 3D U-shaped Wells

ABSTRACT: This study establishes a coupled flow and heat transfer numerical model for a Stereo U-shaped well ClosedLoop Geothermal System (CLGS) to evaluate the impact of working fluids and operating parameters. Results indicate that SCO2 exhibits superior life-cycle heat extraction performance compared to water and R134a, attributed to its high density, low viscosity, and high specific heat capacity in the supercritical region. Parameter sensitivity analysis reveals a unique non-linear heat transfer mechanism for SCO2 systems: driven by the peak specific heat capacity in the pseudo-critical region, optimal efficiency is achieved at an outlet pressure of 10 MPa. Furthermore, increasing flow rates presents a competitive trade-off of exchanging outlet temperature for power gain, while reducing injection temperatures directly enhances performance by maximizing the temperature difference drive. Additionally, the study confirms that formation temperature distribution is dominated by rock thermal conduction and remains insensitive to parameter variations. These findings provide a theoretical basis for efficient deep geothermal exploitation.