Predicting Two‐ and Three‐Fluid Capillary Pressure‐Saturation Relationships of Porous Media With Fractional Wettability

Knowledge of the capillary pressure‐saturation ( P c −S ) relations of porous media is essential for the research and management of multiphase flow and transport. Indirect methods have often been used to predict P c −S curves, since the actual measurement of all P c −S curves may be cumbersome. Existing methods to predict the P c −S relations for porous media with fractional wettability, however, are generally inadequate. This paper reports on methods to quantify P c −S curves of such media that contain two or three fluids (air, oil, and water). The prediction of oil‐water P c −S relations from air‐oil or air‐water P c −S data through mere scaling is not possible since the oil‐water capillary pressure may be positive or negative in fractional wettability media. We successfully predicted the oil‐water P c −S curve using a linear transformation of air‐oil P c −S data. In three‐fluid media with fractional wettability the prediction of three‐fluid from two‐fluid P c −S relations using only Leverett's assumption is unreliable, since both water and oil act as intermediate fluid. We predicted the three‐fluid oil‐water P c from two‐fluid oil‐water or linearly transformed air‐oil P c −S data. The three‐fluid air‐oil P c could be readily predicted from the two‐fluid air‐oil P c −S relation for a variable oil saturation and a constant water saturation. In contrast, when the water saturation was varied, at a constant oil saturation, the air‐oil P c could only be predicted using an empirical correction for the two‐fluid air‐oil P c −S data. The three‐fluid air‐water P c is obtained as the sum of the oil‐water P c and the air‐oil P c (both water and oil pressures are measured with respect to atmospheric pressure).