Modeling Multiscale-Multiphase-Multicomponent Subsurface Reactive Flows Using Advanced Computing
It is becoming increasingly clear that the ability to model multiscale subsurface processes is essential for obtaining an accurate predictive capability of contaminant transport. Predictive modeling of subsurface reactive flows is a daunting task because of the wide range of spatial scales involved - from the pore to the field scale - ranging over more than six orders of magnitude, and the wide range of time scales involved - from seconds or less to millions of years. With uniform grids, large 3D field scale continuum models employing billions of nodes can only resolve features on the order of meters and cannot capture phenomena at much smaller scales on the order of millimeters or less.
This work is aimed at developing the next-generation massively parallel, multiphase, multicomponent reactive flow and transport code based on the successful prototype code PFLOTRAN. PFLOTRAN uses PETSc as the basis for its parallel framework. We are currently extending PFLOTRAN to include a generic multiphase algorithm based on variable switching to incorporate phase transitions for which the user need only add appropriate physical properties for particular phases of interest. Capabilities for both unstructured grids and adaptive mesh refinement on structured grids are being incorporated within PETSc's parallel framework and accessed by PFLOTRAN. Finally, multilevel solver and upscaling capabilities and subgrid scale models are being added to the code.
These enhanced modeling capabilities will improve our understanding of radionuclide migration at the DOE Hanford facility. At Hanford, sub-millimeter-scale mass transfer effects have thwarted attempts at remediation efforts and modeling sequestration of CO2 in deep geologic formations. In these cases, resolving density-driven fingering patterns is necessary to describe accurately the rate of dissipation of the CO2 plume.