A novel fully coupled thermal-hydraulic-mechanical-chemical model for hot dry rock reservoirs based on the non-conforming grid

Non-conforming grids provide an efficient framework for simulating complex fracture networks in hot dry rock (HDR) reservoirs. However, their application to thermal–hydraulic-mechanical-chemical (THMC) coupling remains limited by the difficulty of representing multi-field interactions within reduced-dimensional fractures and by the loose coupling among physical fields. To address these issues, a fully coupled THMC model based on a non-conforming grid framework is developed, integrating the embedded discrete fracture model (EDFM) and the extended finite element method (XFEM). The model enables multi-mineral water–rock reactions and accounts for THMC interactions through both property-parameter coupling and differential-term coupling. In particular, a novel method is presented to characterize the multi-field coupling inside the reduced-dimensional fractures within the non-conforming grid framework. Through explicitly incorporating fracture aperture evolution and fracture-wall contact forces in reduced-dimensional fractures, this method accurately captures the combined effects of contact stress, shear dilation, and mineral dissolution/precipitation on fracture permeability. After verification, the proposed model is applied to a typical HDR reservoir to simulate heat extraction over a period of 25 years. The spatiotemporal evolution of physical fields, variations in fracture properties, and wellhead response characteristics are analyzed. The results demonstrate that the proposed model can effectively capture fracture-dominated THMC coupling processes and long-term performance in HDR reservoirs.