A geochemical transport model for thermo‐hydro‐chemical (THC) coupled processes with saline water

Abstract

Anhydrous MgSO4 is considered as a potential sealing material for the isolation of high‐level‐waste repositories in salt rock. When an aqueous solution, usually a brine type, penetrates the sealing, different MgSO4 hydrates along with other mineral phases form, removing free water from the solution. The uptake of water leads to an overall increase of solid phase volume. If deformation is constrained, the pore volume decreases and permeability is reduced. In order to simulate such processes, especially for conditions without free water, a coupling between OpenGeoSys and thermodynamic equilibrium calculations were implemented on the basis of the commercially available thermodynamic simulator ChemApp and the object‐oriented programming finite‐element method simulator OpenGeoSys. ChemApp uses the Gibbs energy minimization approach for the geochemical reaction simulation. Based on this method, the thermodynamic equilibrium of geochemical reactions can be calculated by giving the amount of each system component and the molar Gibbs energy of formation for all the possible phases and phase constituents. Activity coefficients in high‐saline solutions were calculated using the Pitzer formalism. This model has the potential to handle 1‐D, 2‐D, and 3‐D saturated and nonsaturated thermo‐hydro‐chemical coupled processes even with highly saline solutions under complex conditions. The model was verified by numerical comparison with other simulators and applied for the modeling of SVV experimental data.