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AbstractThis work aims to describe the spatial distribution of flow from characteristics of the underlying pore structure in heterogeneous porous media. Thousands of two-dimensional samples of polydispersed granular media are used to (1) obtain the velocity field via direct numerical simulations, and (2) conceptualize the pore network as a graph in each sample. Analysis of the flow field allows us to distinguish preferential from stagnant flow regions and to quantify how channelized the flow is. Then, the graph’s edges are weighted by geometric attributes of their corresponding pores to find the path of minimum resistance of each sample. Overlap between the preferential flow paths and the predicted minimum resistance path determines the accuracy in individual samples. An evolutionary algorithm is employed to determine the “fittest” weighting scheme (here, the channel’s arc length to pore throat ratio) that maximizes accuracy across the entire dataset while minimizing over-parameterization. Finally, the structural similarity of neighboring edges is analyzed to explain the spatial arrangement of preferential flow within the pore network. We find that connected edges within the preferential flow subnetwork are highly similar, while those within the stagnant flow subnetwork are dissimilar. The contrast in similarity between these regions increases with flow channelization, explaining the structural constraints to local flow. The proposed framework may be used for fast characterization of porous media heterogeneity relative to computationally expensive direct numerical simulations. Article HighlightsA quantitative assessment of flow channeling is proposed that distinguishes pore-scale flow fields into preferential and stagnant flow regions.Geometry and topology of the pore network are used to predict the spatial distribution of fast flow paths from structural data alone.Local disorder of pore networks provides structural constraints for flow separation into preferential v stagnant regions and informs on their velocity contrast. 

Abstract This work investigates the role that pore structure plays in colloid retention across scales with a novel methodology based on image analysis. Experiments were designed to quantify–with robust statistics–the contribution from commonly proposed retention sites toward colloid immobilization. Specific retention sites include solid‐water interface, air‐water interface, air‐water‐solid triple point, grain‐to‐grain contacts, and thin films. Variable conditions for pore‐water content, velocity, and chemistry were tested in a model glass bead porous medium with silver microspheres. Concentration signals from effluent breakthrough and spatial profiles of retained particles from micro X‐ray Computed Tomography were used to compute mass balances and enumerate pore‐scale regions of interest in three dimensions. At the Darcy‐scale, retained colloids follow non‐monotonic deposition profiles, which implicates effects from flow‐stagnation zones. The spatial distribution of immobilized colloids along the porous medium depth was analyzed by retention site, revealing depth‐independent partitioning of colloids. At the pore‐scale, dominance and overall saturation of all retention sites considered indicated that the solid‐water interface and wedge‐shaped regions associated with flow‐stagnation (grain‐to‐grain contacts in saturated and air‐water‐solid triple points in unsaturated conditions) are the greatest contributors toward retention under the tested conditions. At the interface‐scale, xDLVO energy profiles were in agreement with pore‐scale observations. Our calculations suggest favorable interactions for colloids and solid‐water interfaces and for weak flocculation (e.g., at flow‐stagnation zones), but unfavorable interactions between colloids and air‐water interfaces. Overall, we demonstrate that pore‐structure plays a critical role in colloid immobilization and that Darcy‐, pore‐ and interface‐scales are consistent when the pore structure is taken into account.