Research on the solution of the thermo-hydro-mechanical-chemical coupling model based on the unified finite volume method framework

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Heat extraction from hot dry rock (HDR) reservoirs involves complex thermal–hydraulic-mechanical-chemical (THMC) coupling processes, which pose significant challenges for efficient geothermal energy utilization. The current frameworks that combine the finite volume method (FVM) and finite element method (FEM) for THMC modeling based on the embedded discrete fracture model (EDFM) are separate, leading to complex implementations and hindering the development of efficient solutions. To address these issues, we propose an FVM-based THMC coupling model that solves fluid flow, heat transfer, and chemical reactions using the finite volume method (FVM), while mechanical deformation is addressed using the extended finite volume method (XFVM). The reaction module incorporates PHREEQC for multicomponent reactions under high-temperature and high-pressure conditions. The model is validated against experimental data for mineral reactions under high-temperature and high-pressure conditions, as well as XFEM and COMSOL simulations for displacement fields, confirming its accuracy and computational performance. Application results show that the temperature deviation between multicomponent and single-component models can reach up to 14 °C, underscoring the importance of incorporating multicomponent water–rock reactions in THMC coupling. This model accurately captures the spatiotemporal evolution of THMC processes and efficiently predicts long-term heat production in enhanced geothermal systems (EGS) reservoirs. It could significantly advance the ability to achieve more accurate and reliable predictions for the engineering development and efficient utilization of EGS reservoirs.