Das Projekt "Modeling of two-phase flow processes in strongly heterogeneous porous media using multi-rate mass transfer approaches" wird vom Umweltbundesamt gefördert und von Leibniz Universität Hannover, Institut für Strömungsmechanik und Umweltphysik im Bauwesen durchgeführt. Modelling of displacement of one fluid by another immiscible one and mass transfer between the phases is important for many geotechnical applications. An example is the injection of supercritical carbon dioxide into brine. To include the influence of heterogeneous structure that is not resolved by the numerical grid into modelling concepts is a challenge, in particular if parameter contrasts are high. In this proposal we want to derive up scaled model concepts for two-phase flow on large length scales, where we focus on the transition zone between displacing and displaced fluid (the mixing zone) during a displacement problem. The mixing zone is the critical zone, for example, for mass transfer of a dissolved component between the two phases. Based on the models that quantify the mixing zone we want in a second step to analyze the relation between mixing zone volume and interfacial area between the fluids. To derive such model concepts we want to apply multi-rate mass transfer modelling approaches that have been developed to describe solute transport in flow fields with mobile and stagnant flow zones in complexly structured and highly heterogeneous porous media. These approaches have been very successful for linear problems. We want to extend them to the non-linear problem two-phase flow problem.
Project results: Immiscible two phase ï ‚ow processes in highly heterogeneous porous media, such as fractured rock, are important in many geotechnical applications, such as CO2 sequestration or oil recovery. In fractured rock classical modelling approaches are computationally intensive due to the strong contrast in the model parameters. In this project we derived upscaled two phase ï ‚ow models on the macroscale, where the detailed fracture network is no longer described. In fractured rock the fractures are related to fast ï ‚ow processes. Slow exchange of ï ‚uid takes place between the fractures and the rock matrix. For the upscaled model the fractured rock is divided into two zones. The fractures with the fast ï ‚ow processes are the mobile zone and the rock matrix with the slow ï ‚ow processes are the immobile zone. The upscaled ï ‚ow model describes ï ‚ow processes in the mobile zone only. The exchange processes between mobile and immobile zone are modelled with an additional sink-source term. This term is expanded in a way that the model becomes a multi-rate mass-transfer model for two-phase ï ‚ow. With this modelling approach we derived two upscaled models on the macroscale. The ï rst model is for oil recovery from fractured rock. This is an imbibition process, where oil as the nonwetting phase is displaced by water as the wetting phase. The ï ‚ow in the fracture network is dominated by ï ‚ow enforced by boundary conditions and the ï ‚ow in the rock matrix is dominated by capillary counter-current ï ‚ow. The second model is for CO2 storage in deep fractured rock. (abridged text)