Optimization of enhanced geothermal systems with full-wellbore heat transfer

Enhanced geothermal systems (EGS) are a promising technology for exploiting deep hot dry rock resources. In this study, a numerical model of a dual-horizontal-well EGS incorporating full-wellbore heat transfer was developed to investigate thermal evolution, wellbore heat loss, and the effects of key parameters on heat extraction performance. Orthogonal experimental design combined with a normalized weighted scoring method was further applied for multiparameter optimization. The results show that during a 50-year operation period, the reservoir cooling rate decreases from 0.47 to 0.39 °C/year, indicating a transition from rapid thermal depletion to a slower heat decay stage. Parameter analysis reveals clear trade-offs among thermal power, outlet temperature, and long-term thermal sustainability. Increasing the flow rate to 0.035 m3/s improves thermal power by 56.7% but accelerates reservoir cooling, whereas reducing the injection temperature to 20 °C increases thermal power by 26.5%. Increasing well spacing effectively delays thermal breakthrough, while a higher geothermal gradient further enhances heat extraction performance. Range analysis indicates that flow rate is the most sensitive factor affecting cumulative heat production, whereas well spacing plays the dominant role in outlet temperature stability. The optimal balanced parameter combination is a flow rate of 0.030 m3/s, an injection temperature of 20 °C, a well spacing of 300 m, and three fractures. Under this scheme, the cumulative heat production reaches 22.57 PJ and the final outlet temperature is 113.42 °C after 50 years of operation.