We will examine a number of case studies that illustrate both the challenges posed and some exciting ways that advanced computational methods are being brought to bear on these problems. We will examine pore-scale simulations of flow, transport, and reactions in porous media, in which the complex geometry of solid grains and pore spaces is explicitly quantified. Pore-scale models are being used to develop new understanding of fundamental processes that can be incorporated into larger-scale models that treat porous media as effective continua.
We will consider the applicability of two approaches: (1) direct upscaling of pore-scale simulation results using various methods, and (2) multiscale hybrid modeling, in which pore- and continuum-scale models are combined within a single simulation. At the continuum scale, complex geological heterogeneity is expressed at a multitude of scales. For example, in sedimentary aquifers one may observe sediment architectural elements such as lamination (typically millimeter scale), cross-bedding (typically centimeter scale), and larger units such as beds, bed sets, facies, formations, aquifers, and aquitards. We will examine the representation of geologic heterogeneity in reactive transport models, with a focus on the effects of correlated physical and biogeochemical heterogeneity. These issues will be presented in the context of a number of field sites relevant to U.S. Department of Energy contamination problems, including a bacterial transport site, a uranium bioremediation site, and a site with persistent uranium contamination associated with diffusion-controlled mass transfer processes.