Modélisation des couplages entre réactions géochimiques et processus hydrodynamiques en milieu poreux - applications au stockage de CO2 et à l'exploitation d'uranium

摘要

This report is a snapshot after sixteen years of research in the field of reactive transport, since the beginning of my Ph.D. in 1997. The research revolves around two poles : on the one hand the development of the reactive transport code Hytec, on the other hand application of the code in different fields of the Earth Sciences. The first two parts of the report detail several key points from this research work, most of them published or being published, following the dual development/application logic. The last part opens towards interesting future work. Development of a reactive transport code The first part, mostly numeric analysis, details the main features of the code Hytec, in which I have been heavily involved since I joined the laboratory. The underlying equations of the model are given. The resolution methods rely on a finite volume discretization over a Voronoi mesh for the whole hydrodynamic part (flow, transport, heat). Coupling bet- ween chemistry and transport is performed through a sequential iterative scheme. Specific developments are then presented. The feedback of chemistry on transport requires speci- fic coupling treatment to ensure convergence to the correct solution : the effects need to be taken care of within the coupling iterations. Dual porosity simulation can be elegantly simulated by duplicating the chemical nodes. Integrating the simulation of gases have im- plications on the flow- (simultaneous resolution of the pressure and saturation equations), and transport-solver (species in the gas phase independently of the water phase), and finally coupling with chemistry and gas-water equilibrium. Applications The Hytec code is used in various domains of the Earth Sciences, in and out our la- boratory notably by the members of the consortium Pôle Géochimie Transport (Reactive transport group). The document details two families of applications I have been particularly interested in over these years. The geologic storage of CO2 is a potential technology to mitigate greenhouse gas emis- sions. Before the technology spreads out, a demonstration of its efficiency is required. The methods detailed in the document focus of the integrity of barriers : wells and caprock. Uranium exploitation by ISR is a technique used for high reserve but low grade deposits. The economic element is retrieved by circulation of a fluid (e.g. acid) in the ore body. Reactive transport simulation is particularly adapted to describe the system. The work described here aim at simulating the ore formation and its exploitation