Wetting of alkanes on water.

Abstract

AbstractThe wetting behavior of oil on water (or brine) has important consequences for the transport properties of oil in water-containing porous reservoirs, and consequently for oil recovery. The equilibrium wetting behavior of model oils composed ofpure alkanes or alkane mixtures on brine is reviewed in this paper. Intermediate between the partial wetting state, in which oillenses coexist on water with a thin film of adsorbed alkane molecules, and the complete wetting state, in which amacroscopically thick oil layer covers the water, these systems display a third, novel wetting state, in which oil lenses coexistwith a mesoscopic (a few-nanometers-thick) oil film. The nature and location of the transitions between these wetting regimesdepend on oil and brine compositions, temperature and pressure. D 2002 Elsevier Science B.V. All rigths reserved. Keywords: Wetting; Spreading; Wetting transitions; n-alkanes; van der Waals forces; Hamaker constant 1. Introduction and motivationThe wetting behavior of oil on water has a directimpact on oil recovery from underground porousreservoirs and on the processes involved in thecontamination of water-saturated soils by oil. Theinfluence on various oil recovery processes (e.g., gra-vity-assisted drainage, gas injection) of the wettingbehaviorofoilonwaterinthepresenceofgashasbeenthe subject of longstanding interest (Dumore´ andSchols, 1974; Kantzas et al., 1988; Oren et al., 1992,1994; Kalaydjian et al., 1993, 1995; Skurdal et al.,1995;Vizika andLombard,1996).Inthesestudies,thequantity of oil that remains after drainage in porousmedia containing some irreducible (or connate) wateris observed to be lower for complete wetting than forpartial wetting. These results are explained as follows:(1) when oil forms a layer (complete wetting) betweenthe gas phase and the water (brine) phase that coversthe rock (for water-wet porous media), drainage isallowed down to very low residual oil, and (2) whenoilpartiallywetswaterthepresenceofdisconnectedoillenses trapped in the porous medium results in higherresidual oil or, equivalently, lower oil recovery.This wetting behavior refers to flat interfaces. It ischaracterized by the balance of interfacial tensions (orspreading coefficient) S=c