Petroleum Science and Technology, 28:955–968, 2010 Copyright © Taylor & Francis Group, LLC ISSN: 1091-6466 print/1532-2459 online DOI: 10.1080/10916460902937067 Effect of Capillary Pressure on Wetting Film Imbibition Ahead of Main Liquid–Gas Displacement Front in Porous Media M. DONG 1 AND I. CHATZIS 2 1 Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Alberta, Canada 2 Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario, Canada Abstract The effect of capillary pressure on wetting film imbibition along the edges of pores in porous media is investigated experimentally. It is found that the capillary pressure at the main liquid–gas front (the main displacement front) plays a major role, among other factors, in determining the imbibition rate of a wetting liquid along pore edges. The measured velocities of the wetting film in a two-dimensional consolidated glass bead model and the imbibed volumes of the wetting liquid into the mode ahead of the main front are found to be proportional to 1/P 1=2 C and 1/P 5=2 C , respectively, where P C is the capillary pressure at the main liquid–gas front. The effect of capillary pressure on wetting film imbibition along the edges of pores is also illustrated by the experiments in a periodically constricted capillary where different film imbibition rates were obtained when the main liquid–gas meniscus is kept at a throat and a pore. Both theoretical analysis and experimental results show that the length of the wetting film ahead of the main meniscus increases greatly as the injection rate is decreased. Keywords capillarity, capillary pressure, film flow, imbibition, porous media, two- phase flow, wetting 1. Introduction The pore structure of most porous media is generally very complex, and the shapes of pore cross sections are highly irregular. The noncircular nature of both pores and throats in a three-dimensional (3-D) network of pore space permits the accumulation of the wetting liquid and, consequently, flow of the wetting liquid along edges occurs over a large range of saturation due to capillary pressure gradients along the edges (Mason and Morrow, 1991; Dong and Chatzis, 1995, 2003, 2004; Dong et al., 1995; Keller et al., 1997). Under conditions of strongly preferential wetting, the advance of the wetting phase in pore edges and surface grooves ahead of the primary displacing front plays an important role in the removal and trapping of the nonwetting phase (gas or oil) in displacements of very low capillary numbers (Chatzis and Dullien, 1983; Lenormand et al., 1983; Vizika and Address correspondence to M. Dong, Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Dr. NW, Calgary, AB, Canada T2N 1N4. E-mail: mingzhe. dong@ucalgary.ca 955