Study on reservoir permeability sensitivity of injection-production parameters in a CO2-based enhanced geothermal system

Abstract CO 2 -based enhanced geothermal system (CO 2 -EGS) is a potential measure to achieve carbon neutrality and mitigate global warming. The low heat extraction (HE) rate is a major challenge that restricts the development of CO 2 -EGS. Investigating the evolution of reservoir permeability influenced by injection and production conditions is essential for enhancing the HE. Through triaxial seepage experiments, this study investigates the effects of CO₂ injection conditions on the permeability of fractured rock samples. A nonlinear model for effective stress, which accounts for both confining and pore pressures, is proposed. And the sensitivity of rock permeability to these pressures is analyzed. The results indicate that the HE increases permeability when the confining pressure is below 14 MPa. When the confining pressure exceeds 18 MPa, permeability is more sensitive to confining pressure than to pore pressure. Lower injection pressure has minimal impact on permeability before and after HE, while enhancing injection pressure heightens the sensitivity of permeability before HE. Permeability decreases with rising sample temperature and CO 2 injection temperature before and after HE. Lower CO 2 injection pressure and temperature can enhance HE, particularly in high-temperature reservoirs. These findings can offer technical guidance for optimizing injection and production parameters in a CO 2 -EGS.