Influence of thermo–hydro–mechanical coupling on gas migration and energy performance of aquifer compressed air energy storage

Aquifer compressed air energy storage (CAES-A) involves coupled fluid flow, heat transfer, and geomechanical processes, yet the quantitative differences between thermo–hydraulic (TH) and thermo–hydro–mechanical (THM) models remain insufficiently understood, especially under non-isothermal conditions. This study develops a coupled THM framework by integrating TOUGH2/EOS3 with FLAC3D through a Python-based sequential coupling strategy. After validation against the Essen air-flow field test, the framework is applied to the Pittsfield aquifer CAES site to simulate air-bubble formation and injection–withdrawal cycling under isothermal and non-isothermal conditions. Parallel TH simulations are performed to isolate geomechanical effects. The results show that THM coupling has limited influence on macroscopic gas migration, with similar air-bubble geometries predicted by TH and THM models. However, non-isothermal THM coupling significantly enhances porosity evolution, reservoir deformation, and surface uplift through the combined effects of pore-pressure increase and thermal expansion. Thermal effects also strengthen flow–mechanical coupling and increase exergy transfer. Under isothermal conditions, aquifer exergy recovery efficiency (AERE) remains nearly unchanged between TH and THM models, whereas under non-isothermal conditions, THM predicts higher AERE due to enhanced flow capacity and thermal exergy contribution. These findings indicate that TH models are suitable for preliminary gas-migration assessment, while non-isothermal THM models are needed for realistic evaluation of deformation, safety, and energy performance in CAES-A systems.