Petrofisicas

Advances in Water Resources 29 (2006) 212–226 www.elsevier.com/locate/advwatres

Effects of fractional wettability on capillary pressure–saturation–relative permeability relations of two-fluid systems
Sang Il Hwang a, Kwang Pyo Lee b, Dong Soo Lee b, Susan E. Powers
a b c

c,*

Korea Environment Institute, 613-2 BulGwang-Dong, EunPyung-Gu, Seoul 122-706, Republic of Korea Graduate School ofEnvironmental Studies, Seoul National University, Seoul 151-742, Republic of Korea Department of Civil and Environmental Engineering, Clarkson University, 8 Clarkson Ave., Potsdam, NY 13799-5710, USA Received 8 February 2005; accepted 11 March 2005 Available online 15 July 2005

Abstract Capillary pressure (Pc)–saturation (S)–relative permeability (kr) relationships must be quantified toaccurately predict non-aqueous phase liquid (NAPL) distribution in the subsurface. Several experimental techniques are presented here for two-fluid Pc–S–kr relationships for various saturation paths to better define the effect of fractional wettability on these relationships. During the primary drainage path of the Pc–S curves, the air–water system showed no distinct trend as a function of the fraction ofsand treated by organosilane (S) to render it non-water wetting. In a NAPL–water system, however, a consistent decrease of capillary pressure with increase of the fraction of non-water wetting sands was observed. The much lower contact angle for air–water (a–w) system may result in the observed insensitivity of the a–w Pc–S curves to fractional wettability, at least for the PD pathway. For the mainimbibition path of NAPL–water system, capillary pressure decreased as the fraction of the S component increased, requiring forced imbibition (negative capillary pressures) for a certain range of saturations. Systems with an increasing percentage of the S component also exhibited a higher water kr and lower NAPL or air kr at a given saturation for the primary drainage and main imbibition paths inboth air–water and NAPL–water systems. The increase of water kr with increase of the fraction of the S component can be explained by the ability of water to occupy larger and highly conductive pores in such a system. Experimental kr–S data for the primary drainage path of NAPL–water system presented here were used to test the Bradford et al. [Bradford SA, Abriola LM, Leij FJ. Wettability effects ontwo- and three-fluid relative permeabilities. J Contam Hydrol 1997;28:171–91] model and the modified Mualem model for estimating the kr–S curves from measured Pc–S data as a function of fractional wettability. Both models predicted significantly less variation in the kr–S curves than measured indicating that they did not adequately represent the system under investigation. Ó 2005 Elsevier Ltd. Allrights reserved.
Keywords: NAPL; Capillary pressure; Relative permeability; Fractional wettability

1. Introduction The process by which non-aqueous phase liquids (NAPLs) infiltrate into and redistribute within the subCorresponding author. Tel.: +1 315 268 6542; fax: +1 315 268 7985. E-mail address: sep@clarkson.edu (S.E. Powers). 0309-1708/$ - see front matter Ó 2005 Elsevier Ltd. All rightsreserved. doi:10.1016/j.advwatres.2005.03.020
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surface depends on capillary pressure–saturation–relative permeability (Pc–S–kr) relationships. The Pc–S–kr relations are affected by interfacial (or surface) tension and wettability. These interfacial properties can vary considerably due to trace and primary constituents in the NAPL and surface properties of the porous media comprising thesubsurface. Various experimental attempts have been made to quantify trends between

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interfacial properties and Pc–S–kr relationships. The results are conflicting, however, reducing any potential to generalize the overall effects. Several experimental studies have been devoted to quantifying the effect of interfacial tension on...