The use of foam as an effective mobility control agent in enhanced oil recovery applications hinges on its ability to remain stable in the presence of oil. To date, only indirect methods have been used to study this mechanism in porous media, such as pressure drops and foam propagation rates across a core, and these have limitations. This article reports on work carried out to determine directly how oil destabilizes foam in porous media. Micrographs in an etched glass, two dimensional, porous medium micromodel were viewed. The experimental procedure is described. Surfactant foam was injected into a 1.1 mum2 Kuparuk micromodel containing dodecane or hexane at residual saturation, and a microvideo camera apparatus recorded the pore level interactions of foam and oil. It was found that the overall stability of foam was controlled by the stability of the liquid films separating individual foam bubbles and trapped oil blobs. This film is coined a pseudoemulsion film. (J.M.M.)

Direct visual studies of foam flow in etched-glass micromodels containing residual oil demonstrate that foam decays as a result of breakage of pseudoemulsion films. Foam films collapse whenever nearby thin aqueous films separating gas bubbles and oil rupture. Consequently, surfactant formulation for foam insensitivity to oil in porous media should be based on stabilizing pseudoemulsion films.