Numerical study of hydraulic fracturing treatments and geothermal energy extraction from a naturally fractured granitic formation

Abstract

Enhanced geothermal system (EGS) development is an extremely complex process involving reservoir creation and heat extraction. At present, hydraulic fracturing is still the most widely used method to create geothermal reservoirs. We utilize field-measured data from the Gonghe Basin (Northwest China) geothermal field, including drilling data, temperature logging data, and data from lab tests, to perform sensitivity analysis using the 3D fracturing simulator MShale and evaluate different fracturing treatments of a 3.7 km deep granitic formation. The simulation results show that the created reservoir geometry highly depends on the mechanical rock properties, in-situ stress states, and natural fracture systems. The optimum reservoir performances are achieved by analyzing the geological system and performing adequate planning, including a sensitivity analysis of the reservoir rock parameters, natural fracture development status, and in-situ stress states. Wherein the natural fracture development level determines the hydraulic stimulation technique. For the granitic formation in the Gonghe Basin, we found that water fracturing provides the best performance for the formation with highly developed natural fractures, whereas gel-proppant fracturing is more suitable for tight and intact formations. The fracturing treatment affects the production performance of EGSs. The power generation capacity of the formation with highly developed natural fractures treated with water fracturing is 1.61–3.94 MW, whereas that of the formation with few or without natural fractures treated with gel-proppant fracturing is 0.84–2.71 MW.