Session D40 - Poster Session I.
POSTER session, Monday afternoon, March 12
Exhibit Hall, Washington State Convention Center
Foam flow in porous media exhibits striking properties that have been found desirable in many practical undertakings. These properties have been identified as enhanced gas viscosity by virtue of liquid film rheology, and reduced relative gas permeability by virtue of gas trapping. Many previous works treated foam in porous media as bubble trains flowing in a bundle of constricted capillary tubes. Prediction of macroscopic foam rheology can thus be upscaled from liquid film behavior in capillaries. In particular, the modified viscosity of gas in foam was expressed as intrinsic gas viscosity plus additional viscosity imposed mainly by the motion of liquid films through the constrictions of flow channels. The latter was proved (for instance ref. 1) to be directly proportional to pressure drop induced by liquid film curvature. The Young-Laplace relation was then employed to describe the pressure drop over the curved films. The use of this relation results in a maximum pressure drop at the constrictions, explaining the existence of additional viscosity. In this present work, we first develop a simple experimental setup to measure the pressure drop profile induced by one lamella moving through divergent-convergent tubes of varying aspect ratio. The results are surprising because the observed pressure drop profiles are opposite to prediction based on Young-Laplace relation: pressure drop increases when the film is moving downstream from constriction, and falls down when the film motion comes to a halt. Having a better understanding of this phenomenon, we develop a simple mechanical model of lamella motion in constricted tube, taking into account dynamic surface tension and viscous drag at the sidewall of the tube. The simulation results, that show the same trend as observations, address the significant effect of Marangoni surface elasticity and viscosity on dynamic gas viscosity though dynamic lamella tension. On basis of the experimental and theoretical studies, one of our conclusions is that the Young-Laplace relation is inadequate to describe the dynamic viscosity of gas in foam. Rather, it should be used as a static criterion for the onset of lamella mobilization. The overall results of this work are also used as physical background to explain partially the mechanisms of foam resistance and blockage to flow in porous media.
Relevant references: 1. Falls, A. H. Musters, J. J., and Ratulowski, J., SPE Reservoir Eng., 6, 37 (1991) 2. Xu, Q. and Rossen, W. R., 2000 EuroConference on Foams, Emulsions and Applications 3. Rossen, W. R., J. Colloid Interface Sci., 136, 1, 17, 38 (1990) 4. Hirasaki, G. J., and Lawson, J. B., SPE Journal 25, 176 (1985)