A Systematic Study of Alkaline-Surfactant-Gas Injection as an EOR Technique

Abstract

AbstractAlkaline-Surfactant-Polymer (ASP) flooding is an attractive enhanced oil recovery method. However, some reservoir conditions are not favorable for the use of polymers or their use would not be economically attractive due to low permeability or other unfavorable conditions. Foam can be an alternative to polymer for improving the displacement efficiency in chemical-EOR process. The use of foam as a mobility control agent by co-injection or alternate injection of gas and chemical slug is termed, here, as Alkaline-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 ASG process as an enhanced oil recovery technique is relatively new, with very little experimental and theoretical work available on the subject. Polymer is replaced by foam in corefloods experiments as a mobility control agent. Phase behavior and ASG coreflood experiments were carried out to identify high performance chemicals, designed for both foaming and strong IFT reduction performance. The coreflood experiments were performed on sandstone and dolomite rock samples. Oil recovery and coreflood pressure response were evaluated to determine the success of the process. Different injection strategies for foam generation were investigated, and mechanisms of mobility control by foam were studied. Several promising surfactants, with dual properties of foaming and emulsification, were identified and used in the coreflood experiments. Maximum recovery of 95% of remaining oil after waterflood was observed. Oil recovery and pressure responses from ASG experiments are comparable to ASP coreflood experiments carried out under similar conditions. Experimental data show a strong synergic effect of foam and ultra-low oil-water IFT on oil recovery. Compared to polymer, foam has lower cost associated with its use and is less susceptible to biological, shear, and thermal degradation. The use of foam in chemical EOR can reduce the technical disadvantages associated with polymer in low permeability and fractured reservoirs.