Study on Effects of Variable Thermophysical of Water on Heat Extraction Performance of Enhanced Geothermal System

The variation of water thermophysical properties in deep high-temperature enhanced geothermal systems (EGS) is dramatic, which seriously affects the thermal performance of the system. While most previous researches focus on the variation of water density and viscosity with temperature in the reservoir, conversely the pressure effect and other water thermophysical properties are ignored. In this paper, a fully coupled wellbore-reservoir model is presented to explore the influences of the water thermophysical properties varied with temperature and pressure on the system's thermal performance. The model is validated against the 2D single-fracture model analytical solution and field data. The influence of different engineering methods (open-hole length, production pressure) on the system's thermal performance is explored according to the fluid flow and heat transfer mechanisms and thermophysical property analysis. Results show that the pressure difference decreases by 17.66 MPa when the open hole length increase from 20 m to 60 m. Increasing the production pressure would increase the system pressure loss and decreases the system thermal power due to the reduction of water heat capacity. These results provide significant references for the optimization design of the EGS.