Collaborative Research: Fundamental Research on Oscillatory Flow in Hydrogeology

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Collaborative research: Fundamental Research on Oscillatory Flow in HydrogeologyPeter Kitanidis, Stanford UniversityMichael Cardiff, University of WisconsinWarren Barrash, Boise State UniversityThe conventional approach to representing the governing physics of fluid flow in hydrogeology is based on the premises that (a) fluid flow can be treated separately from deformation in the solid matrix and (b) changes in flow conditions are gradual (i.e., allowing simplifying assumptions about momentum changes to be valid). Oscillatory flows may violate these premises in certain "intermediate" frequency ranges, regardless of whether they are created deliberately at a well for purposes of monitoring or site characterization, or are created accidentally from a natural or man-made source. These violations raise important questions for understanding oscillatory fluid flow in subsurface porous media at core and field scales (i.e., scales of interest in hydrologic applications): (a) must Darcy's law be modified? and (b) do controlling hydraulic parameters such as permeability and elastic storage change with oscillation frequency rather than remain constant? This research is a comprehensive study of oscillatory flows at intermediate frequencies involving: a careful mathematical study of flow at the pore scale and upscaling to the core scale to generalize Darcy's law; experiments in a laboratory sandbox to test/validate the theoretical developments and examine heterogeneous cases including infiltration of an immiscible fluid; and upscaling to hydrologic scale with controlled oscillatory flow experiments in the field at a highly characterized research wellfield to test/validate theoretical developments and models. Expected results include a rigorous theoretical treatment of oscillatory flow mechanics leading to predictions and modeling of oscillatory signal propagation characteristics and frequency dependent aquifer parameter behavior at laboratory and field scale for a range of porous media materials. This project has broad impacts for society overall and for the scientific and engineering communities because it deals with basic hydrologic research in the subsurface, where most of the available freshwater is stored. In the United States, groundwater is the primary source of water for over 50 percent of Americans, and roughly 95 percent for those in rural areas. In the world, many of the most important aquifers are being gradually depleted or contaminated. This research will lead to better methods for the restoration and management of this important resource. In particular, oscillatory flows may become important tools for characterization of subsurface volumes to determine the 3D heterogeneity of aquifer parameters and to monitor for changes in water quality or aquifer status without having to remove water (that may be contaminated and hazardous). Oscillatory flows also have potential applications in enhancing mixing, which can enhance reaction rates and result in more efficient site remediation technologies.