Field-scale investigation of CO₂ plume dynamics under spatial wettability variations: Implications for geological CO₂ storage

Subsurface formations typically exhibit heterogeneous wetting characteristics due to the complex pore system, mixed lithology, and prolonged contact with native fluids. This non-uniformity in spatial wettability distribution thus makes the subsurface formations exhibit more complex localized CO₂ /brine/rock interactions, introducing uncertainties in estimating trapping capacity and predicting CO₂ plume migration. Field-scale investigation on the role of wettability in CO₂ geo-storage has received limited attention, and previous studies typically assume an internal uniform wettability condition across the whole formation. However, the more realistic scenario of internal wettability spatial variations within a single formation is yet to be thoroughly examined. In this study, a range of experiment-derived wettability-dependent trapping coefficients were utilized to implement the internal wettability heterogeneity in a single formation model, and its impact on CO₂ plume pattern and trapping efficiency was examined. Furthermore, mixed-wet systems with different CO₂-wet fractions were also considered in this study. The results indicate that internal wettability variations result in changes in the local CO₂ saturation pattern and thus impact the overall plume shape and migration. In addition, the internal heterogeneous wettability system exhibits an approximately 35% reduction and an approximately 20% increase in residual trapping capacity in comparison to internal uniform strongly water-wet and uniform weakly water-wet systems, respectively. An increase in the fraction of CO₂-wet regions in the mixed-wet system results in concentrated high-saturation clusters and reduced local CO₂ residual saturation. This further results in reduced residual and dissolution trapping, followed by a linear correlation.