ABSTRACT
About 9% of world oil production, and virtually all “enhanced oil recovery”, comes from injecting gases, primarily steam and carbon dioxide, into oil reservoirs. Foam can improve the sweep efficiency of injected gases by mitigating or reducing the effects of low gas viscosity and reservoir layering. The mobility-control process, which must treat a large fraction of the reservoir volume, places a heavier emphasis on rapid foam propagation and on chemical costs. Controversy surrounds many of the most basic aspects of foam behavior in porous media. Foam “in bulk” is foam in a container much larger than individual bubbles. Foam in bulk has a yield stress, which arises from the stretching of individual lamellae as bubbles slide past each other in shear flow. For discontinuous-gas foams, the viscosity of the gas itself is insignificant compared to the flow resistance of the lamellae; this resistance is nonetheless accounted as an increase in the effective viscosity of the gas phase.
