Wetting heterogeneity in mixed-wet porous media controls flow dissipation

Pressure controlled displacement of an oil/water interface is studied in dense packings of functionalized glass beads with well-defined spatial wettability correlations. An enhanced dissipation is observed if the typical extension $ξ$ of the same-type wetting domains is smaller than the average bead diameter $d$. Three dimensional imaging using X-ray microtomography shows that the frequency $n(s)$ of residual droplet volumes $s$ for different $ξ$ collapse onto the same curve. This indicates that the additional dissipation for small $ξ$ is due to contact line pinning rather than an increase of capillary break-up/coalescence events.

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