Effects of wettability heterogeneity on multiphase flow: From pore-scale mechanisms to cross-scale insights

Abstract

The macroscopic behavior of multiphase flow systems is governed by interfacial dynamics, which are a strong function of the synergy between viscous forces and wettability. However, the effects of wettability heterogeneity, an inherent feature of natural porous media, remain poorly understood. In this study, we incorporated spatial-related wettability into phase field model and systematically examined the synergy between capillary number (Ca) and wettability heterogeneity on CO₂-water multiphase flow. We developed three phase diagrams to illustrate the evolution of pore-scale displacement mechanisms driven by Ca-wettability-heterogeneity synergy, identifying a novel mechanism termed hybrid filling. Furthermore, we distinguished two types of wetting pinning: p-pinning, resulting from adhesion on patches, and b-pinning, caused by wettability contrasts between patches. These pinnings can enhance the effects of capillary force and contribute to energy dissipation, playing a key role in Ca-wettability-heterogeneity synergy. By clarifying how this synergy affects macroscopic flow characteristics, we established multidimensional diagrams to offer cross-scale insights for Geological Carbon Sequestration (GCS). This work links pore-scale dynamics with large-scale flow behavior, facilitating the design of more effective GCS strategies.