Assessing the effect of capillary suction in foam front displacement within porous media

Foam is often used to displace liquid from porous media, as it produces more stable displacements than using solely gas as a displacing fluid. A model is considered for the foam displacement process in geological applications. The liquid saturation field is divided into an outer region (in which capillary suction effects can be neglected) and an inner region (in which capillary suction effects are retained). The outer region solution exhibits a discontinuous jump in liquid saturation, sometimes referred to as a shock. The inner region solution is a travelling wave that is superposed across that jump. The focus here is upon the inner region. The liquid saturation profile across the inner region is shown to be asymmetric, with abrupt changes for high liquid saturations but gradual changes for lower liquid saturations. These gradual changes should be taken into account when matching onto the outer region. The inner region is predicted to be of small extent, but also accesses fluid mobilities which are much lower than those in the outer region. However, the very lowest mobilities are only attained within a tiny part of the inner region in which saturation is still changing abruptly. In much of the inner region, mobility is only marginally less than in the outer region. Hence, the presence of the inner region does not significantly enhance flow resistance of the foam displacement process. Consequently, the inner region should have little impact on the ability of foam to produce stable displacement processes in porous media.