Emulsions in porous media. I. Transport and stability of polyaphrons in sand packs

Polyaphrons are 'biliquid foams' where micrometer size oil droplets are enc apsulated within a water film. They have large ratios of dispersed phase to continuous phase volume. Polyaphrons require the presence of both an oil p hase surfactant and an aqueous phase surfactant. The aqueous surfactant for ms a soapy shell surrounding the inner oil phase core. The oil phase surfac tant (non-ionic) influences the size of the oil droplets, while the aqueous phase surfactant (anionic or cationic) influences the surface charge of th e polyaphrons. Distinct sizes of oppositely charged polyaphrons were create d by altering the type and concentration of the oil phase and aqueous phase surfactants. The polyaphrons were stable when diluted in deionized water, showing negligible change in diameter after four months of storage. The pol yaphrons were pumped through sand packs to study their stability and flow c haracteristics in a typical porous medium. The surface charge and size of p olyaphrons were found to affect the capture of polyaphrons in the sand and the effective permeability of the sand. The effect of ionic strength was st udied at pH 7.0 with anionic polyaphrons. Increasing ionic strength did not affect the average size of polyaphrons in the effluent, but resulted in sl ightly greater permeability reduction than low ionic strength. Sand packs c onsisting of larger, more uniform size distributions captured less polyaphr ons and had less permeability reduction than smaller, more varied grain-siz ed sand. (C) 2000 Elsevier Science B.V. All rights reserved.