Optimal Use of Supercritical CO2 as Heat Transfer Fluid for Geothermal System

Supercritical carbon dioxide (CO2) is a promising working fluid for geothermal energy extraction due to its superior heat extraction capacity and high fluidity within reservoirs. However, significant thermal energy is lost during transportation along the production well. This study develops a mathematical model coupling heat transfer and CO2 compressibility to investigate strategies for improving heat transfer efficiency from the reservoir to the surface. The influence of mass flow rate (20 kg/s; 25 kg/s and 30 kg/s) and outlet back pressure (8 MPa; 9 MPa and 10 MPa) on system performance is evaluated. Results indicate that the amount of geothermal energy delivered to the surface increases linearly with mass flow rate. Compared to water, CO2 exhibits a 65.5% greater temperature drop along the wellbore but reduces the pressure drop by 50%. A lower outlet back pressure is recommended to enhance both heat transfer and operational safety. The model offers valuable insights into assessing the geothermal potential of depleted high-temperature gas reservoirs.