The Effect of Oil on Foam Stability: Mechanisms and Implications for Oil Displacement by Foam in Porous Media

Abstract

Abstract Foam stability in the presence of Salem crude oil and pure hydrocarbons is investigated as a function of pure hydrocarbons is investigated as a function of chain length of -olefin sulfonates and electrolyte concentration. Interactions between aqueous foam films and emulsified oil droplets are observed using transmitted light, incident light interferometric and differential interferometric microscopic techniques. Foam destabilization factors are identified including the pseudoemulsion film tension and the surface and interfacial tension gradients. Results from foam-enhanced oil recovery experiments in Berea Sandstone cores are presented using the combined gamma ray/microwave absorption technique to measure dynamic fluid saturation profiles. Introduction Three phase foam stability, as has been discussed by numerous authors is of great practical significance. However, despite the recognized significance, the mechanisms by which oil affects foam stability are still under investigation. The effect of oil upon foam stability has been explained in rather general terms through the mechanism of oil spreading phenomena, but the reason why the oil droplets spread and the film between the oil droplets and air bubbles breaks has not been discussed. Our objective in this study is to classify the complex phenomena occurring during the process of three phase foam thinning, to identify the interaction mechanisms between the oil droplets, the thinning foam film and the Plateau-Gibbs borders and the role of surface and interfacial tension gradients in foam stability, and to examine the implications upon crude oil displacement by foam in porous media. During the process of three phase foam thinning, three distinct films may occur: foam films (water film between air bubbles), emulsion films (water between oil droplets) and pseudoemulsion films (water film between air and oil droplets) (Figure 1). To study the behavior of these films and particularly the oil droplet-droplet, oil particularly the oil droplet-droplet, oil droplet-air bubble and oil droplet-foam frame interactions it is necessary to utilize numerous microscopic techniques, including transmitted light, microinterferometric, differential interferometric and cinemicrographic microscopy. EXPERIMENTAL Surfactant-Oil-Electrolyte Systems In this study we used as surfactants alpha-olefin sulfonates C12, C14 and C16 (anionic surfactants, product of Ethyl Corp.) and Enordet AE 1215-30 product of Ethyl Corp.) and Enordet AE 1215-30 (nonionic surfactant, product of Shell Development Co.). For all measurements, the surfactant concentration was chosen at 3.16 × 10(-2) mol/1, several times above the critical micelle concentration (cmc). These particular surfactants (and concentrations) were chosen on the basis of industrial applications. As oil phases we used n-octane (Fisher Sci. Co. reagent grade Lot 746833 class IB) and n-dodecane (Fisher Sci. Co. purified grade Lot 852154), both chosen for their well-defined structure and Salem crude oil, chosen for its practical value. Electrolyte was chosen as NaCl, at two concentrations 0.17 mol/1 (1 wt%) and 0.51 mol/1 (3 wt%). In each study the oil-water system was preequilibrated for one week. preequilibrated for one week.