Foamdrive Seldom Meaningful

With the present interest in foam drive, there is an increasing need for a proper definition and description of foam. A sample of foam is only representative of foam and its bulk properties if it has sufficient size. Foam properties are only relevant with respect to samples over some minimum size and this size is directly related to bubble size. Some direct measurements of bubble size from photographs in the literature gave diameters of ca 200 microns. The theoretical minimum bubble size has been estimated. From the theory on surface active agents the thickness of fluid films should be at least 50 Angstroms, but usually ranges between 200 and 2,000 Angstroms after drainage.