Influence of different fracture morphology on heat mining performance of enhanced geothermal systems based on COMSOL

Abstract

Formation of enhanced geothermal systems (EGS) is the necessary approach to obtain geothermal energy efficiently. In-situ stress, nature of reservoir physical properties and fracturing methods will affect the artificial fracture morphology after reservoir stimulation. A three-dimension thermal coupled seepage model of fractured media was established to simulate the influence of fracture morphology on heat mining performance of EGS, considering the pressure- and temperature-dependent physical properties of working medium. The results indicate that formation of complex fracture network is favorable for heat mining. Production mass flow in Case1 with complex fracture network enhances nearly 2.5 times comparing to the unenhanced model at exploitation beginning. The total net energy rate will up to 44 MW and be maintained above 10 MW for 5 years. The system impedance can be effectively reduced, however the sustainable heat mining duration decreased to 30 years. The increase in length and number of branch fractures is expected. While increasing the width of branch fractures deliberately has little effect on the exploitation of EGS. Finally, we investigate the adaptability of employing supercritical CO2 in EGS with complex fracture network. Production mass flow will be enhanced 3–5 times compared with water, but the stability is poor, total net energy rate decrease from 90 MW to 3 MW over the 10-year operation period.