Physcial Sciences Division
Research Highlights

April 2015

Simulating Subsurface Flow and Transport at Multiple Scales

New method shows events occurring in a large sample at the resolution of soil grains

Subsurface Flow and Transport. By bridging the gap between small and large spatial scales, the simulation method could pave the way for more accurate assessments of the risk of groundwater contamination and the development of more effective remediation strategies. Figure shows a comparison of solute transport simulations using binary segmentation (left image) and ternary segmentation (right image). Enlarge Image.

Results: Scientists at Pacific Northwest National Laboratory introduced a method that overcomes the computational challenge of simulating subsurface phenomena that occur at both the scale of tens to hundreds of microns-the size of solid soil grains and pore spaces-and at much larger scales. The researchers presented the first simulations of pore-scale flow and transport over a large, decimeter-scale volume.

Why It Matters: By bridging the gap between small and large spatial scales, the simulation method could shed light on the effect pore-scale processes have on field-scale phenomena. This new method could pave the way for more accurate risk assessments of groundwater contamination and development of more effective remediation strategies.

Methods: The researchers performed multiscale simulations of pore-scale processes over a decimeter-scale volume of natural porous media with a wide range of grain sizes. They compared simulation results to findings from column experiments on the same sample. The researchers used X-ray computed tomography (XCT) to non-invasively image the sample and executed high-performance codes on a supercomputer to carry out the simulations. Because the XCT could not provide sufficient spatial resolution to identify pore spaces within fine-grained regions containing silt and clay, the team developed a multi-level segmentation approach in which the core was segmented into solid, pore, and porous solid regions. They evaluated two XCT image segmentation strategies: binary segmentation, which resolved pores and solids; and ternary segmentation, which resolved porous solids with pores smaller than the imaged resolution. They found simulations based on ternary segmentation, but not binary segmentation, provided results consistent with experimental observations, demonstrating their ability to successfully model pore-scale flow over a column-scale domain.

What's Next? The researchers are continuing to make advances using this method, working to transfer knowledge of small-scale physical processes to larger-scale phenomena and dramatically improving the capability of numerical models to accurately predict behavior in complex systems.

Acknowledgments

Sponsor: This research was supported by Department of Energy, Office of Science, Office of Biological and Environmental Research as part of its Subsurface Biogeochemical Research (SBR) Program. This contribution originates from the SBR Scientific Focus Area at PNNL.

Facilities: The column experiments were performed in the Subsurface Flow and Transport Experimental Laboratory at EMSL. Computations described here were performed using computational facilities of the PNNL Institutional Computing program and the National Energy Research Supercomputing Center (NERSC), which is supported by the DOE Office of Science under contract DE-AC02-05CH11231. Sediment imaging was performed at the High-Resolution X-ray CT Facility, an NSF-supported multiuser facility at the University of Texas at Austin.

Research Team: Timothy Scheibe, William A. Perkins, Marshall C. Richmond, Matthew I. McKinley, Pedro D.J. Romero-Gomez, Mart Oostrom, Thomas W. Wietsma, John A. Serkowski, and John M. Zachara, Pacific Northwest National Laboratory.

Research Area: Subsurface Science

Reference: Scheibe TD, WA Perkins, MC Richmond, MI McKinley, PDJ Romero-Gomez, M Oostrom, MW Wietsma, JA Serkowski, and JM Zachara. 2015. "Pore-Scale and Multiscale Numerical Simulation of Flow and Transport in a Laboratory-Scale Column." Water Resources Research 51(2):1023-1035. DOI: 10.1002/2014WR015959