Lithium is a critical chemical element that plays a key role in the energy transition. It is one of the main components of batteries for electric vehicles, for which global demand continues to grow. According to the French Ministry of Ecological Transition, the supply of critical metals, and lithium in particular, will be increasingly strategic for the French economy of tomorrow. Among the potential sources of lithium identified in France, those from geothermal brines circulating in the deep reservoirs of the Upper Rhine Graben (URG) appear particularly promising.
The exploitation of deep geothermal reservoirs involves hydrodynamic, thermal and chemical disturbances that need to be predicted to insure the long-term lifespan of these reservoirs. Numerical modelling is a powerful tool to assess these perturbations with non-linear effects. The 3D coupled thermo-hydrodynamic-geochemical simulations envisaged in the project will aim to account for the reciprocal effects of thermal, hydrodynamic and geochemical processes in the reservoir during its exploitation like, for instance, porosity/permeability changes due to dissolution/precipitation reactions whose kinetics are promoted by temperature.
In the specific geological context of the Upper Rhine Graben, such simulations will be done by means of the development of a coupling between a thermo-hydrodynamic code adapted to fractured media, namely the ComPASS software , and a geochemical code, namely PhreeqC. ComPASS is based on recent developments to simulate multiphase and multicomponent hydrothermal transfers. Simulations can be carried out on unstructured meshes including complex fracture networks, in which the flow is two-dimensional, coupled to the three-dimensional flow in the porous matrix (hybrid model). For the geochemical code PhreeqC, modules (i.e., IPhreeqC and PhreeqC-RM ) have been specifically developed to facilitate its coupling with hydraulic and transport codes. Both ComPASS and PhreeqC codes have been developed to enable parallel calculations.
The post-doctoral work consist in implementing a sequential non-iterative approach (SNIA) coupling of ComPASS and PhreeqC relying on PhreeqC-RM. In addition to managing the balance of materials, charges and heat during information exchange, the coupling must consider that changes in fluid chemistry can induce dissolution/precipitation reactions affecting rock porosity and permeability, and consequently fluid circulation.
