Alkali-Surfactant-Gas Injection as a Novel Enhanced Oil Recovery Technique
Quoc P. Nguyen, Gary A. Pope
Conventional Alkaline-Surfactant-Polymer (ASP) flooding is an attractive enhanced oil recovery method. However, a significant fraction of reservoirs, such as naturally fractured carbonates with low matrix permeability, are not suitable candidates for the use of polymers.
In addition, the use of polymer for very high salinity and high temperature formations may not be economically feasible. Foam can be an alternative to polymer for improving the displacement efficiency in chemical-EOR processes. The use of foam as a mobility control agent by co-injection or alternate injection of gas and chemical slug is termed, here, as the Alkali Surfactant Gas (ASG) Process. Foam reduces the relative permeability of the injected chemical slug that forms microemulsion at ultra-low oil-water interfacial tension (IFT) and generates sufficient viscous pressure gradient to drive the foamed chemical slug. The concept of using the ASG process as an enhanced oil recovery technique is relatively new, with very little experimental and theoretical work available on the subject. New surfactant structures with dual properties of foaming and emulsification, and alkali metaborates have been developed and used in coreflood experiments. Maximum recoveries of 95% of remaining oil after waterflood were observed, indicating a strong synergic effect of foam and ultra-low oil-water IFT on oil recovery.