Thermodynamic modeling of multiphase thermo-hydro-mechano-chemical models with viscoelastoplastic rheology

The ongoing energy transition and technological advancements present increasingly complex challenges for numerical modeling, necessitating the development of multi-physics, multi-scale approaches. Recent progress in high-performance computing has catalyzed the rapid evolution of a new generation of numerical codes designed to tackle these multifaceted problems. However, this progress demands revisiting and refining constitutive models to ensure they are rigorous, thermodynamically consistent, and suitable for computational implementation. A critical aspect of these models is addressing the coupling between fluid flow, rock deformation, chemical reactions, and heat exchange. Specifically, the influence of chemical reactions on porosity evolution and mechanical closure relations requires robust theoretical frameworks. Reservoir rocks experience elastic deformation when subjected to the small pressure changes caused by fluid injection. Elastic deformation affects the reservoir's pore space and permeability, influencing fluid migration and storage capacity. Viscous deformation occurs over time as rocks like salt, shale, or certain clays flow plastically under subsurface conditions. During prolonged CO₂ or H₂ storage, viscous creep can change reservoir geometry, potentially altering caprock integrity and leakage risks. Plastic deformation occurs when the rock is subjected to stresses beyond its yield strength, leading to permanent changes in the reservoir structure. Elevated injection pressures can cause shear failure, inducing fractures or reactivating pre-existing faults, which may compromise containment and pose seismic hazards. This necessitates incorporating elastic, viscous, and plastic rheological behavior into the model. Multiple fluid phases within pore spaces add additional layers of complexity, demanding meticulous attention to thermodynamic consistency in governing equations. This work investigates the thermodynamic admissibility of a multi-phase, coupled thermo-hydro-mechano-chemical model that integrates viscoelastoplastic deformation. Using established thermodynamic principles, we derive closure relations and develop a comprehensive set of governing equations. These equations are formulated to maintain thermodynamic rigor while being optimized for computational efficiency and implementation.