Reactive transport in damageable geomaterials: thermal-hydrological-mechanical-chemical coupling of geological processes

[Truncated abstract] Numerical modelling is a powerful tool to improve geological understanding, as it is particularly well suited to simulate and visualise complex scenarios, to validate or refute hypotheses in conceptual models, and in turn to raise more scientific questions and to help make predictions. No code exists however which can simulate nature in its full complexity. Some of the most challenging problems toward that goal consist in modelling accurately the coupling feedbacks between all processes involved, including mechanical deformation, fluid flow in porous media, heat transfer, chemical transport and fluid-rock chemical interactions. Thermodynamics focuses on energy, the common denominator between all processes, and therefore provides an ideal framework to couple them all in a consistent manner. Within this approach, all physical processes can be described through the definition of their free energy and dissipation functions. This theoretical framework is used to introduce a new mathematical formulation of continuum damage mechanics (CDM) for geomaterials subjected to thermomechanical loading, implemented using a custom user material subroutine of ABAQUS/- Standard (2008). The material's rheology includes isotropic linear elasticity as well as non-linear visco-plasticity induced by combined creep mechanisms. The formulation is based on the theory of generalized standard materials where the dissipative processes obey the principle of maximum dissipation. A second numerical approach, escriptRT, is developed to simulate reactive transport in porous media based on a finite element method (FEM) using the flexible and scalable escript package, combined with three other components: (i) a Gibbs minimisation solver for equilibrium modelling of fluid-rock interactions, (ii) an equation of state for pure water to calculate fluid properties and (iii) a thermodynamically consistent material database to determine rocks material properties...