Thermo–Hydro–Mechanical–Chemical Coupling in Reactive Fractured Rocks With Double Porosity

Abstract

The coupled thermo–hydro–mechanical–chemical equations are developed for reactive fractured rock with double porosity. The constitutive equations explicitly account for the effects of solid‐phase reactions (e.g., dissolution, precipitation) on the stress‐strain response and porosity evolution by reactions in both the fracture and the porous matrix. The model naturally reduces to existing thermo‐poroelastic formulations in the absence of solid reactions, providing a unified description for reactive and non‐reactive processes. The theoretical formulation is derived from the Helmholtz free energy of the reactive media, which is obtained by the fundamental principles of thermodynamics and the quantified entropy production. Numerical simulations of quartz dissolution under repository‐like conditions show that the pressure field reaches a quasi‐steady state within approximately 50 days, whereas the concentration field requires more than 5,000 days to approach dynamic equilibrium at 293.15 K. After 50,000 years, the reaction‐induced strain at 333.15 K reaches approximately 6.5 × 10−4, more than six times that at 313.15 K and about 70 times that at 293.15 K. These results indicate that diffusive fracture–matrix exchange controls long‐term solute redistribution, while temperature strongly amplifies reaction‐induced deformation. The proposed framework provides a mechanistic basis for linking chemical alteration to the long‐term thermo‐hydro‐mechanical behavior of fractured rocks in deep geological environments.