An Investigation of Oil Destabilization of Nitrogen Foams in Porous Media

Abstract

Abstract When applied as conformance treatments, foams are required to effectively reduce gas injectivities over prolonged periods of time. Frequently, this ability must be manifested in the presence of a residual oil saturation which often exerts a destabilizing effect on foam and the capacity to generate foam. In this study, the capacity to generate and sustain foam in the presence of a residual oil saturation was examined by each of two methods. The first method monitored the in-situ generation of nitrogen foam at constant pressure drop for 1-ft Berea cbres at a residual oil saturation to surfactant. Gas mobility reduction, foam longevity, and the rate of foam decay were quantified for a variety of surfactants and oils at constant salinity and concentration at room temperature. The second procedure involved the constant quality injection of pregenerated foams into Berea cores at residual oil saturation to water flooding. The liquid requirement to reach steady state and the absolute pressure drop were determined under test conditions identical to the aforementioned method. In each method, foam stability showed a strong sensitivity to surfactant, oil type, in-situ foam quality and oil desaturation kinetics. In a companion laboratory study, the degree of correlation between these results and a variety of benchtop measurements was established. Benchtop measurements included interfacial and surface tensions, film elasticities, oil spreading, pseudoemulsion film drainage times, and film disjoining pressure for oil equilibrated and nonequilibrated surfactant solutions. From these studies, it is concluded that foam destabilization by oil is dictated primarily by pseudoemulsion film stability. The relative stability of the pseudoemulsion films in-situ, however, is dependent upon the prevailing pore level conditions of oil and liquid saturation. Oil spreading, wave dampening, and lamellar film strength had little effect on foam stability to oil. Given this information, one can easily choose test design criteria upon which to screen surfactants for foam conformance treatments in the presence of oil.