The morphology of non-equilibrium foam and gelled foam lamellae in porous media

Low energy, replica-based and cryogenic scanning electron microscopy, and reflected visible light and fluorescence modes of confocal laser scanning microscopy, were applied to the imaging of mobile, non-equilibrium polymer-thickened and gelled-foams in porous media. As a result information was obtained about the morphology of some non-equilibrium foam lamellae in real porous media. In contrast to equilibrium (or near-equilibrium) foam, the structure of these non-equilibrium, viscous foams flowing through porous rock is quite similar to that observed in etched-glass micromodels. The foam films are lamellar, three-dimensionally arranged in various structures, and exhibit foam lamellae thicknesses ranging from about 1-12 mu m. This thickness range is much narrower than is observed for bulk dynamic foams. The present measurements also show that foam lamellae in porous media can extend for considerable distances, greater than the length of individual pores, if oriented parallel to the overall direction of flow. In other cases, foam lamellae can span across the entrances to multiple pores. In the context of improved oil recovery, the latter configuration would cause blocking and diverting of injected fluids whereas the former configuration would cause only reduced permeability of the pores to injected fluids. These results are important to the optimal design of polymer-thickened and delayed-gelling foams for water shut-off applications in the near-wellbore regions of oil and gas producing wells, and for blocking and diverting applications in reservoirs undergoing secondary and tertiary flooding processes. (C) 1999 Elsevier Science B.V. All rights reserved.