Predicting two- and three-fluid capillary pressure-saturation relationships of porous media with fractional wettability
1996
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-oil Pc-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).
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