Hybrid numerical methods for multiscale simulations of subsurface biogeochemical processes

Many subsurface flow and transport problems of importance today involve coupled non-linear processes that occur in media exhibiting complex heterogeneity. Problems involving biological mediation of reactions fall into this class of problems. Recent experimental research has revealed important details about the physical, chemical, and biological mechanisms that control these processes from the molecular to laboratory scales. We are developing a hybrid multiscale modeling framework that combines discrete pore-scale models (which explicitly represent the pore space geometry at a local scale) with continuum field-scale models (which conceptualize flow and transport in a porous medium without a detailed representation of the pore space geometry). At the pore scale, we have implemented a parallel three-dimensional Lagrangian model of flow and transport using the smoothed particle hydrodynamics method and performed test simulations using millions of computational particles on the supercomputer at the Environmental Molecular Sciences Laboratory. We have also developed methods for gridding arbitrarily complex pore geometries and simulating pore-scale flow and transport using parallel implementations of grid-based computational fluid dynamics methods. Within the multiscale hybrid framework, we have coupled pore- and continuum-scale models to simulate coupled diffusive mixing, reaction, and mineral precipitation, and compared the results with conventional continuum-only simulations. The hybrid multiscale modeling framework is being developed using a number of SciDAC enabling technologies including the Common Component Architecture, advanced solvers, Grid technologies, scientific workflow tools, and visualization technologies.