Foam flow through an oil-wet porous medium. A laboratory study

A laboratory study of the steady generation and flow of gas and surfactant solution through an oil-wet porous medium indicates that foam is formed and is effective in reducing gas permeability. A comparison of the flow characteristics of foam in oil-wet and water-wet media showed that at similar surfactant concentrations gas permeability reduction in both systems is approximately equal. The ability to form stable foam in situ in an oil-wet porous medium appears to result from the alteration of the initially hydrophobic surface to hydrophilic by two mechanisms: surface tension reduction and surfactant adsorption. Wettability alteration of the hydrophobic surface is evidenced by a dramatic shift in liquid relative permeability when surfactant is present in the aqueous phase. The liquid relative permeability curve of the oil-wet porous medium, in the presence of surfactant, essentially matched that of the water-wet porous medium. Such shifts in liquid relative permeability have not been observed for foam flow in strongly water-wet porous media. No alteration in either liquid or gas relative permeability occurred with added surfactant when a residual mineral oil was present in the oil-wet system. Transient measurements, however, indicated the formation of foam in the water-wet system when residual oil was present.