Experimental studies have shown that the steam-foam process can be enhanced significantly by injecting a suitably formulated alkali/surfactant mixture in the aqueous phase of steam. Emulsionscreening tests, corefloods, and flow-visualization experiments using an alpha olefin sulfonate (AOS) surfactant with 16–18 carbon, Na2CO3, and a heavy Californian crude have shown that alkaline steam foam offers significant advantages over regular steam foam by combining the benefits of thermal and chemical enhanced-oil-recovery (EOR) processes.
First, Na2CO3 reduces surfactant consumption by adsorption by rendering the clay surface more negatively charged. Second, by precipitating divalent ions that get ion exchanged off the clays, Na2CO3 reduces surfactant consumption by precipitation. Third, a suitably formulated alkali/surfactant system reduces the oil/water interfacial tension (IFT) sufficiently to enable the heavy oil to be emulsified into the aqueous phase in the presence of steam. This oil-in-water emulsion is less viscous than the oil alone and can be readily transported. Consequently, the residual-oil saturation (ROS) is reduced to a value less than that of steam. Fourth, this lower ROS reduces the destabilizing effect of oil on foam, resulting in stronger steam foam that provides better mobility control than regular steam foam. Therefore, it has the potential to further reduce steam gravity override. Fifth, the reduction in gravity override also reduces loss of heat to the cap rock, thereby improving steam utilization.
When applied to steamdrive, alkaline steam foam has the benefit of increasing foam-propagation rate, improving mobility control, improving steam use, and reducing the ROS. Potential applications of alkaline steam foam to steam soaks and steam-assisted gravity drainage (SAGD) are also discussed.