Utah FORGE: Hydrogeothermal modeling of a granitic based discrete fracture network

Enhanced geothermal systems (EGS) are engineered reservoirs that have been stimulated to extract efficiently heat from low permeability hot rock. Generating efficient hydraulic pathways for heat exchange is crucial. A 3-dimensional Discrete Fracture Network (DFN) model was developed for simulating and determining the optimum hydraulic fracture network for the proposed Phase 3 injection and production wells at a Frontier Observatory for Research in Geothermal Energy (FORGE) site in Utah. Numerical simulations are used to study hydrogeothermal transport in the fractured media. The effect natural fractures contribute to hydraulic fracture growth were studied in regard to changes in natural fracture intensity, flow rate, hydraulic pathways, permeability, and perforation cluster spacing. Post hydraulic fracturing networks are incorporated into a hydrothermal modeling package where a possible range of heat extraction values are determined from the reservoir over a 30-year production period. Results suggest that DFN modeling in an EGS setting has exceptional value. The study serves as a benchmark for developing an improved understanding of the effects of the existing FORGE natural fracture systems. The simulations suggest an optimized pumping schedule that generates conductive post-stimulation fracture networks between hypothetical Phase 3 injection and production wells and establishes an effective hydrological thermal model under various fluid flow conditions. A more viscous fluid increases the fracture height and significantly effects fracture growth in the middle cluster. Injection temperature and flow rate are two of most important parameters that control the production temperature and heat recovery.