Field-informed THMC modeling of heat extraction from a deep fractured carbonate geothermal reservoir in Xiongan

Deep fractured carbonate reservoirs are promising geothermal resources, but their production performance is controlled by coupled fluid flow, heat transfer, stress evolution, fracture-aperture change, and water-rock reactions. This study develops a field-informed thermo-hydro-mechanical-chemical (THMC) model to investigate heat extraction and operational scenarios in the Gaoyuzhuang carbonate reservoir, using Well D22 in the Xiongan New Area as a representative case. The model couples Darcy flow, advective-conductive heat transport, thermo-poroelastic deformation, stress-dependent fracture permeability, and simplified calcite-based carbonate dissolution/precipitation. Available temperature data were used for thermal calibration, whereas hydraulic, mechanical, and chemical responses are interpreted as scenario-based coupled-process results. The calibrated model achieved MAE = 2.4 °C, RMSE = 3.1 °C, and R 2 = 0.97. Results indicate that fracture aperture and injection rate jointly control heat-sweeping efficiency and thermal breakthrough. An aperture range of approximately 2–3 mm produced favorable thermal performance under the assumed conditions, whereas larger apertures promoted preferential flow. Simplified geochemical feedback further modified fracture transmissivity through dissolution or precipitation. This work provides a process-based framework for evaluating coupled THMC behavior in fractured carbonate geothermal reservoirs.