Reactive transport and mixing in heterogeneous media: chemical random walks under local non-equilibrium
Understanding and modelling reactive transport in porous media is fundamental to predicting field-scale biogeochemical reactions, which play a key role in current environmental issues such as water resources management and carbon dioxide sequestration. A major scientific challenge is to capture the dynamics of coupled solute mixing and reaction processes in the context of multiscale heterogeneity, which characterise most natural porous media. In particular, the impact of pore-scale mixing on large- (Darcy-)scale reactive transport is a critical scientific question. ChemicalWalks addresses this question by coupling for the first time the lamella theory of mixing, developed by the host supervisor, and the chemical CTRW model for reaction kinetics under incomplete mixing, recently developed by the ER. While the lamella theory has successfully quantified mixing processes and fluid-fluid reactions at pore scale, its application to fluid-solid reactions, which are ubiquitous in natural systems, remains to be explored. The key idea of ChemicalWalks is to use the lamella theory to determine how pore-scale concentration distributions control the distribution of fluid-solid reaction rates, and formalize a predictive theory for upscaled reaction kinetics through the chemical CTRW framework (WP1). The complementary expertise of the researcher and the host will ensure a particularly efficient two-way transfer of knowledge to achieve this goal. This will open the door to the development of a hybrid computational method, quantifying the effect of pore-scale mixing on Darcy-scale reactive transport phenomena at a scale relevant to environmental applications (WP2). ChemicalWalks will be firmly rooted on a career development plan and supported by scientific training in state-of-the-art mixing theories and data processing and interpretation techniques, placing the fellow at the forefront of reactive transport modelling.