Multi-objective optimization of seasonal high-temperature aquifer thermal energy storage: a full thermo-hydro-mechanical coupling study with evolving porosity

High-temperature aquifer thermal energy storage (HT-ATES) is an underground thermal energy storage technology capable of large-scale, long-duration, and seasonal operation. It holds significant promise for integrating renewable energy sources and supporting building heating demands. However, most existing models assume constant reservoir porosity, which limits the accurate characterization of reservoir structural evolution under long-term cyclic operation and precludes assessment of its consequent impacts on system performance. To address this limitation, a full coupled thermo–hydro–mechanical (THM) numerical model incorporating dynamic porosity evolution was developed. This model was employed to conduct long-term simulations of a double-well HT-ATES system. The simulation results reveal that, over the first year of operation, the average production temperature predicted by the variable-porosity model is 3.75 °C lower than that obtained from the fixed-porosity counterpart. Furthermore, after ten years of operation, the peak temperature near the warm well stabilizes at approximately 96 °C, the far-field reservoir temperature increases from 40 °C to approximately 55–60 °C, and the stress-disturbed zone expands continuously outward. Subsequently, operational optimization was performed with the dual objectives of maximizing thermal recovery efficiency (TRE) and minimizing injection pressure. The optimization results demonstrate a synergistic regulatory interplay between injection temperature and injection rate. By appropriately matching their respective operating windows, both thermal performance and operational cost-effectiveness can be simultaneously improved.