Capillary Pressure–Saturation Relations for Saprolite: Scaling With and Without Correction for Column Height

Abstract

controlled by capillarity, any attempt to predict DNAPL behavior in a porous medium requires determination of Dense nonaqueous phase liquids (DNAPLs) are important subsur-the capillary pressure–saturation relationship, hereafter face contaminants. Information is lacking on DNAPL behavior in heterogeneous porous media such as weathered rock (saprolite). We denoted by ␪ w (h c), where ␪ w is the volumetric content of measured air–water and Fluorinert (a nontoxic DNAPL surrogate; the wetting fluid and h c is the capillary pressure head. The standard procedure for measuring ␪ w (h c) consists close to saturation on an 18-cm-long by 10-cm-diameter undisturbed of introducing a nonwetting fluid at a known pressure column of interbedded sandstone and clayshale saprolite. The Camp-into a porous medium, waiting for an equilibrium condi-bell empirical model was fitted to both ␪ w (h c) relations. The resulting tion, and then determining the wetting phase saturation best-fit parameters were 19.54 and 30.10 cm of H 2 O for the displacement capillary pressure head (h 0) and 0.029 and 0.045 for the pore-procedure produces one pressure–saturation data pair. size distribution index (1/b), for the air–water and Fluorinert–water Additional data pairs are produced by incrementing the data, respectively. Corresponding model parameters corrected for the nonwetting fluid pressure. The data pairs are then used hydrostatic fluid distribution within the column were 14.08 and 15.96 cm of H 2 O for h 0 , and 0.026 and 0.034 for 1/b. The correction procedure to construct a static equilibrium drainage curve that de-had a large effect on the Fluorinert–water ␪ w (h c) relation and relatively scribes the capillary behavior of the sample. Such curves little impact on the air–water ␪ w (h c) relation. Parameters from the are often parameterized using empirical expressions for air–water relations were used to predict Fluorinert–water ␪ w (h c) rela-the ␪ w (h c) relation such as the Brooks and Corey (1964) tions using the expression: (h 0) 2 ϭ (␴ 2 /␴ 1)(h 0) 1 , where (h 0) 1 , (h 0) 2 and equation, the Campbell (1974) equation, and the van ␴ 1 , ␴ 2 are the capillary displacement pressure heads and interfacial Genuchten (1980) equation. The majority of pressure cell studies involving DNAPL– showed that direct measurements of the Fluorinert–water ␪ w (h c) rela-water systems have been performed on homogeneous tion need to be corrected for column height. The corrected Fluorinert– water ␪ …

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