The Utah FORGE (Frontier Observatory for Research in Geothermal Energy) project, a U.S. Department of Energy initiative located near Milford, Utah, aims to advance EGS technology. In April 2024, eight new stimulation stages (Stages 3R–10) were conducted in well 16A, following the initial stimulation series (Stages 1–3) in April 2022. Microseismic catalogs and fiber optic data reveal that the fractures stimulated in Stages 3R–6 closely align with that initially generated during Stage 3, suggesting reactivation of existing fractures rather than creation of new fractures in this recent stimulation campaign. To investigate this hypothesis, we adopt a coupled thermo-hydro-mechanical and earthquake (THM+E) simulation workflow to analyze the stimulation activity in well 16(A)78-32, with the primary objective to confirm whether Stages 3R–6 reactivated fractures initially formed in Stage 3. The workflow comprises two sequential modeling steps. Specifically, the first step involves a continuum-based fully coupled THM simulation that incorporates an upscaled permeability field to represent discrete fracture networks. The THM simulation outputs are then post-processed and transferred to an earthquake simulator to model the induced seismic events. Numerical results have illustrated acceptable agreement with the field injection pressure for each stage, when the THM modeling setup includes previously stimulated fracture in the simulation of subsequent stages. Additionally, the full THM+E simulations were conducted, with the purpose to compare the seismic catalog with the field observation. The simulation results have demonstrated a moveout pattern of seismic events away from the injection point through Stages 3–5, showing quantitative similarity to the field observation. Conclusively, these coupled simulation results support the hypothesis that the recent stimulation stages may not generate new fractures, but instead reactivated the same fracture formed in the previous Stage 3 stimulation.

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