Structure/Performance Relationships for Surfactant Stabilized Foams in Porous Media

Abstract While much is known about foam performance in porous media some key knowledge-gap areas remain, one of which is the relationship between surfactant and foam performance in porous media. We compare the viscosities of two different types of polymer-thickened foams in laminar pipeline (bulk) flow versus the same foams flowing in consolidated sandstone rock. For one kind of surfactant-stabilized foam, the apparent viscosity in the rock is an order of magnitude greater than the viscosity of the "same" foam in pipeline flow. However, for another kind of surfactant, the foam apparent viscosity in the rock is very similar to the viscosity of the "same" foam in pipeline flow. Using advanced imaging techniques, various core samples from each kind of experiment were examined. It was found that the morphology of the second kind of foam was consistent with an effective foam viscosity that was comparable to that experienced in laminar-flow, pipeline loop experiments. On the other hand, the morphology of the first kind of foam contained features consistent with the order of magnitude higher viscosity found for its flow in rock versus flow in the pipeline loop. Our measurements show that at least part of the explanation for the observed differences among different surfactant systems with respect to bulk flow versus constrained flow is foam morphology. This work is important to the specification and formulation of the most effective surfactants for varying applications including mobility control, blocking and diverting. Introduction Stable aqueous foams are required in a variety of industrial processes, particularly in the petroleum industry's improved oil recovery (IOR) applications. A major challenge in formulating an effective foaming agent is the proper selection of surfactants. Harsh chemical environments are sometimes present in oil reservoirs and several hundred papers have been published in the past thirty five years identifying desirable foam-forming characteristics. These are reviewed elsewhere for harsh1,2 and less demanding environments3. The foaming capability of a surfactant relates to both foam formation and foam persistence, which are influenced by many bulk and interfacial physical properties4. Unfortunately, it is generally found that the performance of foams in porous media is not easily predicted on the basis of these physical properties5, although they can be exploited to increase foamability and foam persistence. For example, water-soluble polymers can stabilize foams by increasing either the surface or bulk viscosity of the film, thereby increasing the film elasticity or decreasing the film drainage rate. They are often effective at lower concentrations than other organic additives, and more compatible with different types of foaming systems. Polymer-thickened foams have been increasingly utilized in IOR with some commercial success6. In IOR, the unique physical structure and surface properties of foam produce a high flow impedence that improves the efficiency of crude oil production. The physical properties of the foam films likely play an important, as yet poorly defined, role in the passage of foam through porous rock. Many laboratory investigations into the generation of foam in porous media have been carried out using a variety of media.