Application of phase behavior studies to optimize chemical formulation for heavy oil EOR is not very common due to difficulties in identifying micro-emulsion in the presence of highly viscous and opaque crude oil. Currently, selection of ASP system for heavy oil EOR is mostly based on IFT value when other selection criteria such as surfactant adsorption, and chemical compatibility, are met. This omission of phase behavior study in the evaluation process can often lead to poor choice of chemical system since the quality of the micro-emulsion generated by the system is unknown and may not exhibit the critical properties (viscosity, stability) required to mobilize capillary trapped heavy oil.
This paper presents laboratory procedures for the optimization of ASP system for EOR of a viscous (>10,000 mPa.s) and high TAN (> 2 mg KOH/g) heavy oil using both phase behavior studies and IFT measurements. The resulting optimized ASP system, when mixed with the candidate heavy oil, displays Winsor type phase behaviors comparable to light oil/ASP system. These Winsor type III heavy oil micro-emulsions are stable and have much lower viscosity (150 - 350 mPa.s) than their parent crude oil. During the phase behavior study, it was observed that the natural petroleum soap from the crude oil plays an important role in the formation of the micro-emulsion and lowering of IFT. Effective utilization of petroleum soap presents in the crude oil during chemical EOR will dramatically reduce chemical cost and improve surfactant propagation within the reservoir. Recovery of the viscous heavy oil from Berea core with this optimized ASP system was excellent (~80%). The ability of this ASP solution to recover capillary trapped oil was demonstrated from the amount of incremental oil produced from a Berea core sample which had been extensively flooded with polymers. To our knowledge, identification of well characterized and thermodynamically stable Winsor type III micro-emulsion from heavy oil/ASP system has not been reported previously. Results from this study can lead to development of improved procedure for optimization of chemical system for heavy oil recovery.