Spatially distributed wettability characterization in porous media.

Abstract

Multiphase displacement in porous media is governed by local wetting, yet its spatial variability in situ remains difficult to quantify. In micro-CT imaging, wettability is characterized by a geometric contact angle, but estimating contact angles is challenging since the three-phase contact loop is difficult to identify due to partial-volume effects and uncertainty in the segmentation. Existing methods cannot reliably resolve pore-scale heterogeneity in wettability. We introduce a novel automated geometric algorithm to measure the contact angle pore-by-pore contact angle that bypasses explicit detection of the contact loop by extrapolating surface normals from neighboring two-phase interfaces, reducing sensitivity to segmentation errors. The method is validated on synthetic datasets and applied to water-wet and mixed-wet rocks. We quantify measurement uncertainty arising from mesh smoothing and segmentation, and show that smaller pores amplify uncertainty. Wettability heterogeneity broadens the contact angle distribution because local wetting varies across the pore space. Our workflow produces spatially resolved contact angle maps that reveal heterogeneity masked by bulk averages; in a mixed-wet sample with a mean contact angle of 64.7°-conventionally classified as weakly water-wet-40% of pore space lies in the intermediate-wetting regime (70-110°), explaining the coexistence of minimal interfaces and mixed filling mechanisms. Open-source software is also provided enabling accurate wettability characterization for CO₂ sequestration, hydrogen storage, and multiphase flow applications.