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

Polyaphrons are ‘biliquid foams’ where micrometer size oil droplets are encapsulated within a water film. They have large ratios of dispersed phase to continuous phase volume. Polyaphrons require the presence of both an oil phase surfactant and an aqueous phase surfactant. The aqueous surfactant forms a soapy shell surrounding the inner oil phase core. The oil phase surfactant (non-ionic) influences the size of the oil droplets, while the aqueous phase surfactant (anionic or cationic) influences the surface charge of the polyaphrons. Distinct sizes of oppositely charged polyaphrons were created 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 polyaphrons were pumped through sand packs to study their stability and flow characteristics in a typical porous medium. The surface charge and size of polyaphrons were found to affect the capture of polyaphrons in the sand and the effective permeability of the sand. The effect of ionic strength was studied at pH 7.0 with anionic polyaphrons. Increasing ionic strength did not affect the average size of polyaphrons in the effluent, but resulted in slightly greater permeability reduction than low ionic strength. Sand packs consisting of larger, more uniform size distributions captured less polyaphrons and had less permeability reduction than smaller, more varied grain-sized sand.