Relative Permeability Trends in Different Dolomite and Limestone Formations

Abstract Imbibition relative permeability plays a crucial role as an input parameter in dynamic simulation models. Relative permeability curves are assigned to various grid blocks in the model based on the reservoir rock type. The goal of this paper is to provide experimental uncertainty ranges for the relative permeability curves observed in dolomite and limestone formations from a carbonate field in the Middle East. Representative samples were selected from various formations in Abu Dhabi to measure steady-state relative permeability under reservoir conditions. The relative permeability data were rigorously assessed and quality-checked using pressure data and in-situ saturation monitoring. The plugs were carefully selected to represent the main porosity-permeability distributions in the cored intervals. Porosity values of the samples ranged from 0.10 to 0.30 (fraction), while absolute permeability varied between 0.50 mD and 255 mD. The samples were classified based on porosity, permeability, thin-section analysis, and high-pressure mercury injection. All the dolomite and limestone formations exhibited similar porosity-permeability ranges, though the dolomite samples displayed more uniform pore- throat size distributions. The dolomite and limestone samples showed similar initial oil saturations (0.80 to 0.90) and end-point oil relative permeability (0.70 to 0.90). Residual oil saturation ranged from 0.10 to 0.20. However, the end-point water relative permeability (Krw(Sor)) varied differently across the different lithologies. For the dolomite samples, Krw(Sor) was more consistent, ranging from 0.40 to 0.60. In contrast, limestone samples showed a clear correlation between Krw(Sor) and rock permeability, with Krw(Sor) increasing as absolute permeability increased. The limestone samples exhibited greater variation in both oil and water relative permeabilities, with changes exceeding one order of magnitude at a given saturation. The Corey exponents for oil and water (no and nw) ranged from 3.1 to 5.5 and 2.3 to 3.8, respectively. The dolomite samples displayed less variation, as all the samples could be modeled with a single Corey function (no = 4.5, nw = 3.5). This study emphasizes the significance of carbonate rock type-based relative permeability measurements across different lithologies and geological textures, from mudstones to packstones and grainstones. It also provides experimental uncertainty ranges that can be applied to similar rocks, which are often lacking in proper reservoir simulation modeling.