资源环境科技发展态势分析平台

Natural porous media possess spatial heterogeneous (fractional) wettability, which controls the multiphase flow behavior, i.e., displacement and trapping. We used mixed hydrophilic (contact angle θ = 0°) and hydrophobic (θ = 100°) 1 mm sands and 1mm glass beads as model systems for fractional wet porous media. Both porous media have the same morphological characteristics (Minkowski functions). A comparative μ-CT study of such fractional wet systems is lacking in the literature. A previous study (Geistlinger and Zulfiqar, 2020) showed a percolation transition of the invading fluid from compact to fractal displacement when the wettability changed from imbibition to drainage. This correlates to a transition from no to maximal trapping. For the first time, we observed in fractional wet glass bead packs, a second structural percolation transition with a percolation threshold of approximately 50% hydrophobic glass beads. Below this threshold, the percolating cluster consisted of hydrophilic glass beads, which resulted in compact displacement without any trapping. Above the threshold, the percolating cluster consisted of hydrophobic glass beads, which resulted in fractal displacement with maximal trapping. Trapping occurred only in hydrophobic environments/configurations, i.e., when the trapped clusters were surrounded by hydrophobic glass beads. Fractional wet glass beads and sands show an opposite trapping behavior, i.e. the trapping efficiency increases for glass beads, whereas it decreases for sands with increasing percentage of hydrophobic grains. Interestingly, the trapping efficiency approaches the same limit value for pure hydrophobic sands and glass beads. This demonstrates that bypass trapping is the dominant trapping mechanism, because it depends strongly on the pore connectivity.

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