Abstract: To address the issues of flow loss and resource waste during geothermal extraction in water-based enhanced geothermal systems,CO₂ was selected as the heat transfer fluid for the CO₂-plume geothermal system. Through methods such as heat transfer experiments,dissolution experiments,and post-CO₂ flooding gas-water relative permeability curve evaluation experiments,the heat transfer performance of supercritical CO₂ under different conditions and the dissolution effect of CO₂ aqueous solution on rocks were quantitatively assessed. Additionally,the heat-carrying capacity and heat extraction rate of CO₂ and water were evaluated. The study shows that under the condition of the same mass flow rate of the heat transfer fluid,when the injection temperature is 24 ℃,the heat transfer efficiency of CO₂ is over 27% higher than that of water;when the injection temperature is 35 ℃,the heat transfer efficiency of CO₂ is over 8% higher than that of water,indicating that CO₂ has higher heat transfer efficiency and heat-carrying capacity than water. When the formation pressure of the gas reservoir rises to 25 MPa,the heat capacity value of CO₂ is 0.45 times that of water,and its mobility is 2.5 times that of water,making CO₂′s heat extraction advantage more pronounced. The dissolution reaction of CO₂ with chlorite is strong,leading to an increase in the pore space and permeation channels of the core,effectively enhancing the reservoir permeability,strengthening the convection of fluids in the pores,and improving the heat transfer efficiency. This study provides a fundamental theoretical basis for the application and promotion of CO₂-plume geothermal resource extraction technology.

Key words: geothermal, CO₂-plume geothermal system, CO₂ storage, dissolution, CCUS