Foamdrive Seldom Meaningful

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Abstract
Summary: With the present interest in foamdrive, there is an increasing need for aproper definition and description of "foam." A sample of foam isrepresentative of foam and its bulk properties only if it has sufficient size. To take an extreme, a microscopic sample out of the middle of a gas bubble isnot "foam." Bulk properties such as gas content, viscosity, etc., canbe determined only on samples sufficiently large to contain many bubbles, counted in all three dimensions. Foam properties are relevant only with respectto samples over some minimum size, and this size is related directly to bubblesize. Discussion: Some direct measurements of bubble size from photographs in the literaturegave diameters of about 200 micron. We also have estimated the theoreticalminimum bubble size. In a flow experiment, of course, we can observe foam before it enters a coreand we may see foam being formed where gas and liquid leave a core. Within theporous rock there is two-phase flow, but there is seldom reason to believe thatthis flow can be described by a quasi singlephase flow of a "foam" showing the same viscous behavior as measured macroscopically outside the rock. Conclusions: Where authors claim that a so-called foamdrive yields a higher oil recoverythan normal two-phase flow, we may have to find another explanation. Althoughthe mechanical structure of foam may break down upon entrance into a porousmedium, the chemical composition still differs from a conventional gas/watercombination through the presence of surface-active agents.

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