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

Abstract

Knowledge of the capillary pressure‐saturation (Pc−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 Pc−S curves, since the actual measurement of all Pc−S curves may be cumbersome. Existing methods to predict the Pc−S relations for porous media with fractional wettability, however, are generally inadequate. This paper reports on methods to quantify Pc−S curves of such media that contain two or three fluids (air, oil, and water). The prediction of oil‐water Pc−S relations from air‐oil or air‐water Pc−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 Pc−S curve using a linear transformation of air‐oil Pc−S data. In three‐fluid media with fractional wettability the prediction of three‐fluid from two‐fluid Pc−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 Pc from two‐fluid oil‐water or linearly transformed air‐oil Pc−S data. The three‐fluid air‐oil Pc could be readily predicted from the two‐fluid air‐oil Pc−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 Pc could only be predicted using an empirical correction for the two‐fluid air‐oilPc−S data. The three‐fluid air‐water Pc is obtained as the sum of the oil‐water Pc and the air‐oil Pc (both water and oil pressures are measured with respect to atmospheric pressure).