Numerical investigation on power generation performance of enhanced geothermal system with horizontal well

Abstract

• Combined with thermodynamic cycle, EGS-ORC coupling model is proposed. • The optimal operation parameters of EGS-ORC are obtained. • The effect of various parameters on the performance of ORC system is probed. Enhanced geothermal system (EGS) can efficiently extract heat stored underground, while Organic Rankine Cycle (ORC) system can generate electricity with heat extracted by EGS. A combination of underground heat extraction and ground power generation systems is proposed in present work. The underground heat extraction system that consists of an EGS coupled with hydraulic-thermal horizontal wells and five disc-shaped fractures. The ground power generation system is comprised of a basic ORC system, and R245fa is used as the working fluid. The performance of combined system is numerically investigated in present work. The results indicate that with the increase of geothermal fluid mass flow rate, the geothermal fluid outlet temperature decreases rapidly, and the thermal reservoir life exhausts more earlier. In addition, the optimization of EGS is conducted as well, and the optimal case with the maximum production temperature has been obtained. It’s found that when the mass flow rate and injection temperature of geothermal fluid are 30 kg/s and 50 °C respectively, the production temperature of considered EGS drops to 441.3 K after thirty years of operation, the increase in pump power consumed by transporting geothermal fluid rises to 0.53 MW, and the net output power of ORC system drops to 895 kW. Furthermore, it’s found that the geothermal fluid mass flow rate has an obvious influence on the power generation performance. In addition, a sensitivity analysis of the three considered parameters (production pressure, fracture distance, well spacing) has been performed, which reveals that well spacing has the greatest effect on EGS power generation performance.