Thermo-hydro-chemical coupling model of acid treatment in complex carbonate geothermal reservoirs

Permeability reduction due to mineral scaling, particle migration, and geochemical interactions is a critical challenge in carbonate geothermal reservoirs, significantly affecting the efficiency of Enhanced Geothermal Systems. Acid treatment is widely used to restore permeability by dissolving blockages and creating wormholes, thereby improving reservoir flow and heat transfer. However, existing acidizing models often neglect the effects of fracture blockage and reaction heat. To address these gaps, this study develops a thermo-hydro-chemical coupled model that integrates fluid dynamics, acid transport, thermal effects, and acid-rock reactions in a two-dimensional representation of a fractured carbonate geothermal reservoir. The model is formulated using the Stokes-Brinkman equation, the first and second laws of thermodynamics, Fick's law, the Arrhenius equation, and the Kozeny-Carman relationship to accurately capture wormhole propagation. A grid independence study ensures numerical stability, and the model is validated against published experimental results, confirming its reliability in predicting acid-rock interactions. Simulation results reveal that fracture blockage significantly alters acid flow paths, and if permeability within blocked fractures falls below that of the surrounding matrix, acid bypasses the fractures, increasing acid treatment costs. Furthermore, reaction heat plays a crucial role in wormhole propagation, with elevated temperatures accelerating acid consumption and altering dissolution patterns. The study also emphasizes the necessity of real-time monitoring of fracture conditions, as sudden changes in injection pressure or production flow rate may indicate blockage formation requiring intervention. This study provides theoretical guidance for efficient acid treatment in carbonate geothermal reservoirs.