Experimental study of convective heat transfer of carbon dioxide at supercritical pressures in a horizontal rock fracture and its application to enhanced geothermal systems

Enhanced geothermal systems create fractured reservoirs to extract economic quantities of heat from low-permeability and/or low-porosity geothermal resources. Convective heat transfer characteristics of fluids at supercritical pressures in rock fractures are important for optimizing the heat transfer model, which is a key tool for simulating heat extraction and improving the heat recovery factor for such projects. This paper presents the results of experimental investigations of laminar convective heat transfer of CO2 at supercritical pressures in a horizontal fracture with an aperture of 0.2 mm. The laboratory apparatus operated at temperatures up to 280 °C, fluid pressures up to 14 MPa, and confining pressures up to 28 MPa. The effects of mass flow rate and initial rock temperature on the rock wall and fluid temperatures were examined. A method was proposed for processing the experimental data and local heat transfer performance in the fracture was obtained. Considering the effects of variations in thermophysical properties, a correlation of heat transfer performance in the rock fracture was proposed to improve field simulation models for enhanced geothermal systems.