Reactive transport modelling has wide applications in geosciences. In the field of hydrogeology, it has been utilised to simulate the biogeochemical processes that disperse and degrade contaminants in the aquifer. For geotechnical applications, such as geological CO2 sequestration, the reaction of CO2 with the ambient saline aquifer determines the final success of storage. In a radioactive waste repository, scientists rely on reactive transport models to predict the mobilisation of hazardous radionuclides within space and time. In this work, the multi-component mass transport code OpenGeoSys, was coupled with two geochemical solvers, the Gibbs Energy Minimization Selektor (GEM) and the Biogeochemical Reaction Network Simulator (BRNS). Both coupled codes were verified against analytical solutions and simulation results from other numerical models. Moreover, the coupling interface was developed for parallel simulation. Test runs showed that the speed-up of reaction part had a very good linearity with number of nodes in the mesh. However, for three dimensional problems with complex geochemical reactions, the model performance was dominated by solving transport equations of mobile chemical components. OpenGeoSys-BRNS was applied to a two dimensional groundwater remediation problem. Its calculated concentration profiles fitted very well with analytical solutions and numerical results from TBC. The model revealed that natural attenuation of groundwater contaminants is mainly controlled by the mixing of carbon source and electron donor. OpenGeoSys-GEM was employed to investigate the retardation mechanism of radionuclides in the near field of a nuclear waste repository. Radium profiles in an idealised bentonite column was modelled with varying clay/water ratios. When clay content is limited, Ba-Sr-Ra sulfate solid solutions have a very strong retardation effect on the aqueous radium. Nevertheless, when clay mineral is abundant, cation exchange sites also attract Sr and Ba, thus dominates the transport of Ra.

Parmi les options en cours d’investigation, le stockage souterrain de l'hydrogène dans les formations sédimentaires comme les grès pourrait offrir un potentiel unique pour stocker de grandes quantités d'énergie. L'évaluation des modalités de stockage souterrain de l'hydrogène nécessite donc à la fois une connaissance précise des transformations minéralogiques dues à la présence de l'hydrogène et l’acquisition de données sur le comportement hydrodynamique des fluides. Par conséquent, cette étude se composera de trois parties : 1- Etude des interactions géochimiques de l’hydrogène dans des formations sédimentaires gréseuses : Les produits expérimentaux portent la marque d'une réaction très limitée entre les minéraux du grès et l'hydrogène. Si les résultats expérimentaux sont combinés aux résultats numériques, l’étude démontre que l'hydrogène, une fois injecté, peut être considéré comme relativement inerte. De façon globale, nos résultats renforcent la faisabilité du confinement de l'hydrogène dans des réservoirs géologiques comme les grès. 2- Etude de la migration de l'hydrogène dans les grès : détermination de la perméabilité relative et de la pression capillaire du système hydrogène-eau : Afin de fournir des données quantitatives pour le développement du stockage souterrain de l'hydrogène, la pression capillaire et la perméabilité relative ont été mesurées pour le système hydrogène-eau en deux conditions potentielles. Les résultats indiquent que les données obtenues sont applicables à l’ensemble des conditions de stockage de l'hydrogène. 3- Modélisation numérique d’un site de stockage géologique d’hydrogène : La simulation numérique a été effectuée pour caractériser l'évolution dynamique d’un site de stockage d'hydrogène pur. Une fluctuation saisonnière du fonctionnement du réservoir et l'effet des fuites d'hydrogène dus aux réactions ont été pris en compte. / Underground hydrogen storage has been introduced as storage solution for renewable energy systems as it offers a unique potential to store large amounts of energy, especially in sedimentary formations such as sandstones. However, evaluating the underground hydrogen storage requires a precise knowledge of the hydrodynamic behavior of the fluids and of mineralogical transformations due to the presence of hydrogen that may affect the storage properties. Therefore, this study is consists in three parts: 1- Study of geochemical reactivity of hydrogen in sandstone sedimentary formations: The experimental products bear the mark of only very limited reaction between sandstone minerals and hydrogen. Taken together with the numerical results, this study demonstrates that hydrogen, once injected, can be considered as relatively inert. Overall, our results support the feasibility of hydrogen confinement in geological reservoirs such as sandstones. 2- Study of the migration of hydrogen in sandstone: determination of relative permeability and capillary pressure of hydrogen-water system: To provide quantitative data for the development of underground hydrogen storage, capillary pressures and relative permeabilities of hydrogen-water system have been measured at two potential conditions. The interpretation of the results would suggest that the obtained data are applicable for the entire range of hydrogen storage conditions. Interfacial tensions and contact angles for the hydrogen-water system have been also derived. 3- Numerical simulation of a geological hydrogen storage site: The numerical simulation was performed to characterize the evolution of pure hydrogen storage, by considering the seasonal fluctuation of renewable energy and the effect of hydrogen loses due to the biotic reactions.