Wettability Effects on Capillarity and Relative Permeability in different Carbonate Rock Types

Summary In carbonates, heterogeneity complicates the task of reservoir description and thus necessitates the establishment of accurate understanding of geology and wettability, and their effects on petrophysical properties. The objective of this research work is to evaluate wettability and its effects on capillarity, saturation and relative permeability in different dolomite and limestone reservoir rock types. Representative samples were selected based on CT imaging, porosity-permeability data, thin-section descriptions and high-pressure mercury injection capillary pressure curves. Core samples’ porosity values ranged from 0.15frac to 0.35frac, while absolute water permeability varied between 1 mD and 1000 mD. The different samples gave similar initial oil saturations (i.e., ∼ 0.90 fraction) and similar endpoint oil relative permeability (i.e., 0.70 to 0.88). Residual oil saturation (Sor) ranged from 0.10frac to 0.20frac, and endpoint water relative permeability (Krw(Sor)) varied between 0.30 to 0.60. The dolomite samples showed a tendency towards more oil-wetness while the limestone samples showed intermediate wetting conditions. The petrophysical properties showed major variations only when wettability varied between oil-wet to water-wet. Samples with weakly oil-wet to strongly oil-wet conditions did not demonstrate major changes in their petrophysical properties (i.e., Sor and Krw). The measurements provided insights into wettability and its effects on flow and capillarity.