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United States Department of Agriculture

Agricultural Research Service


item Bradford, Scott
item Leij, Feike

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Organic liquids in the subsurface environment pose a significant threat to the soil and our groundwater supplies. Consequently, considerable research has been devoted to model the movement and fate of organic contaminants. Such models require knowledge of the capillary pressure(Pc)-saturation (S) relations, which relate the pressure difference between fluids to their volumetric fractions. The measurement of Pc-S relations may be quite cumbersome if more than two fluids are present, such as for air-water-oil-soil systems. Alternatively, Pc-S curves are predicted from data for simpler systems. Methods for predicting Pc-S relations in contaminated soil systems commonly assume that the solid surface preferentially absorbs water. However, for most soils this is not the case. This paper outlines and tests a method for predicting and modeling the Pc-S relationships for soils consisting of different fractions of solids that absorb water or oil. Results are important for those trying to predict the movement of organic liquids in the subsurface.

Technical Abstract: Knowledge of the capillary pressure (Pc)-saturation (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. This paper reports on predictive methods for quantifying Pc-S curves in two- and dthree-fluid media with mixed wettability. Scaling approaches to predict the two-fluid Pc-S relations for porous media with mixed wettability are generally inadequate since they assume the wettability (contact angle) is saturation independent. We successfully predicted the oil-water Pc-S relation using a linear transformation of the air-oil Pc-S data. Prediction of the three-fluid from two-fluid Pc-S relations using Leverett's assumption was not possible in mixed wettability due to the spatial dependency of the intermediate fluid. Alternatively, we found that the oil- -water Pc could be predicted from two-fluid oil-water Pc-S data or from the linearly transformed two-fluid air-oil Pc-S data. When the oil saturation was varied, at a constant water saturation, the three-fluid air-oil Pc could be readily predicted from the two-fluid air-oil Pc-S relation. 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 was obtained from the experimental constraints on the three-fluid capillary pressures; both water and oil pressures are measured with respect to atmospheric pressure, and the oil-water Pc is therefore equal to the difference of the air-water Pc and the air-oil Pc.

Last Modified: 08/23/2017
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