Multiphase Inverse Modeling In Structured Soils and Fractured Rocks

Reliable predictive modeling of subsurface flow and transport requires accurate representation of relevant processes, and accurate description of the soil or rock structure. Inverse modeling is considered a viable approach to obtain site-specific, process-relevant, and model-related parameters that appropriately characterize subsurface formation properties and the variably saturated system state. However, quantifying variably saturated flow remains conceptually and numerically challenging, especially in structured soils and fractured rocks. These media exhibit complex, multi-modal pore-size distributions, large contrasts in hydrologic properties between low- and high-conductive features, and multi-scale heterogeneity with both random and deterministic spatial patterns. Inherent differences in the structure of soil and rock materials call for different simulation and characterization approaches. We will (1) provide an overview of conceptual models used to capture unsaturated flow in multi-porosity media, (2) discuss joint inversion approaches for concurrent estimation of soil structure and unsaturated flow properties, and (3) present examples of multiphase inverse modeling studies in fractured rocks. The studies reveal the need for collecting complimentary data to be jointly analyzed and used for improved characterization and prediction of flow and transport in structured soils and fractured rocks. This work was supported by the U.S. Dept. of Energy under Contract No. DE-AC02-05CH11231.