Physical and Chemical Effects of an Oil Phase on the Propagation of Foam in Porous Media

Abstract

Abstract Laboratory experiments were performed to determine the effects of a residual oil phase to hot nitrogen flood an the propagation of surfactant foam in Berea sandstone rocks. Static phase behavior-type tests were performed in support of the displacement tests. In the static experiments, surfactant partitioning into the oil phase and thermal degradation losses were measured. The chemical and physical properties of the oil phase were varied by the employment of four crude oil and two synthetic oil samples. The chemical properties of the surfactant phase were varied by the employment of three different foaming sulfonate surfactants. Each oil was analyzed for composition and physical and interfacial properties were measured. The effect of the presence of an oil phase on foam propagation was found to be strongly surfactant-specific. Implications of the results on the mechanisms controlling oil production in reservoirs containing steam override zones and channels are discussed. Introduction Foams are used for steam mobility control in both steam drive and cyclic operations. Many mechanisms governing the flow of foam through porous media are not yet understood. One of these is the effect of oil on foam stability and consequently on foam flow in porous media where oil is present. Oil-foam, interactions are complex. The presence of oil can be detrimental to foams. First, the surfactant can preferentially partition into the oil phase, away from the gas-water interface, and destabilize the foam bubbles. Second, polar components, in the oil may adsorb at the gas-water interface instead of the surfactant. If these oil components have poorer foam-stabilizing properties than the surfactant, they will destabilize the foam. Third, oil could spread at the gas-water interface, resulting in a reduction of the local surface tension, thereby causing thinning and rupture of bubble lamellae by the Marangoni effect. Fourth, oil droplets can be located at strategic sites in the porous media where bubble snap-off is most likely to occur, thereby hindering generation or regeneration mechanisms. As the residual oil saturation is reduced, more channels can then be invaded by the foam bubbles. The requirement that foam coexists with high oil saturations depends on the application. In a mature steam drive, foam injection could reduce steam mobility in the oil-depleted zones (less than 15% Sor) of the reservoir (override or isolated channels Then, it could be undesirable to block the higher oil saturation regions with foam and reduce oil mobility in the reservoir. In other cases (channels resaturated by oil gravity drainage or override zones with higher oil saturations than found in mature steamfloods), it may be necessary to generate a foam in the presence of high oil saturation (less than 15%) to increase the resistance of steam in the charnels and override zones. In all cases, understanding the mechanisms of oil production in the reservoir will help in the selection of the best suited surfactant for a specific application. In this paper, foam propagation is investigated in Berea sandstone at residual oil saturation. Three surfactants with varying ability to foam in the presence of oil were studied. Four crude oil and two synthetic oil samples were used. P. 473^