The enhanced geothermal system heat mining prediction based on fracture propagation simulation of thermo-hydro-mechanical-damage coupling: Insight from the integrated research of heat mining and supercritical CO2 fracturing

Abstract

• Integrated research of HDR fracturing and EGS heat mining in field-scale is realized. • Heat mining based on fracture propagation simulation of THM-D coupling is launched. • Heat mining of SCO 2 fractured EGS and hydraulic fractured EGS is explored. • Synchronous fracturing and asynchronous fracturing in doublet-well EGS is compared. Due to the two key stages involving the enhanced geothermal system (EGS) development: the HDR fracturing stage and the EGS heat mining stage after fracturing, it is necessary to conduct the integrated research of heat mining and EGS fracturing for the accurate prediction of EGS productivity. Based on the THM-D coupling, we carry out the field-scale fracture propagation of HDR, and then launch the research on heat mining evaluation based on the obtained fracture morphology. Firstly, the fracture morphology and the corresponding heat mining performance obtained by hydraulic and SCO 2 fracturing are compared by synchronous fracturing of doublet-well. Subsequently, the impact of fracturing procedure, duration, velocity and in-situ stress on fracture propagation of SCO 2 fracturing and the EGS heat mining performance after fracturing is studied. The results show that the SCO 2 fracturing can reduce the fracture connection time by 77.01% and increase the damage area of 16.1% compared with hydraulic fracturing. Compared with asynchronous fracturing, the synchronous fracturing can save the fracturing time by 51.2% and increase the fracture surface area by 5.99%. The increase of 10 MPa in horizontal stress difference enhances the fracture surface area by 1.37%, the corresponding heat mining rate increase by 7.01%.