The problems associated with many gas injection projects are the inefficient gas utilization, poor sweep efficiency and low incremental oil recovery due to viscous instabilities (channeling or fingering) and gravity segregation. These are caused by rock heterogeneity as well as the low density and viscosity of the injected gas. To mitigate these drawbacks foam can be injected into the oil reservoir by co-injection of surfactant solution and gas, or by surfactant-alternating-gas (SAG) mode. When the foam films are created in-situ, the flow of gas is hindered and gas can sweep the pores that would not be reached in the absence of foam – better vertical and areal sweep. The efficiency of the displacement process in foam-assisted gas flood depends largely on the longevity of the created foam films, and ratio of film destabilization and re-generation rates. Experimental studies have demonstrated the detrimental impact of oil on foam stability. This paper reviews the mechanisms and theories (disjoining pressure, coalescence and drainage, entering and spreading of oil, oil emulsification, pinch-off, etc) suggested in the literature to explain the impact of oil on foam stability in the bulk and porous media. Moreover, we describe the existing approaches for foam modeling in porous media and the ways these models use to describe the oil effect on foam propagation in porous media.

Further, we present various ideas on an improvement of foam stability and longevity in the presence of oil. The outstanding questions regarding foam-oil interactions are pointed out.

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