Are Field Polymer Enhanced Oil Recovery Projects Reaping the Benefits of Residual Oil Saturation Reduction Due to Polymer Viscoelasticity?

For polymer solutions used in enhanced oil recovery (EOR), viscoelasticity is a rheological phenomenon that has a strong flux dependency and has been tied to significant reductions in residual oil saturation (Sor) during laboratory corefloods at high flux conditions. However, an unanswered question is whether the polymer’s viscoelastic effects reduce Sor over a significant portion of a polymer-flooded reservoir.

Two methodologies are used to answer this question for polymer-flood projects across nine countries (Argentina, Austria, Canada, China, India, Oman, Russia, Suriname, and USA). For most polymer floods with horizontal injectors, the highest possible Darcy velocity is too low (0.01–0.2 ft/D) to reach the onset velocity for viscoelastic behavior (>1 ft/D for most field conditions). For most vertical polymer injectors, less than 1% of the reservoir experiences fluid velocities high enough for viscoelasticity to potentially be important.

This paper conveys the improbability of shear-thickening induced-viscoelasticity causing Sor reduction in field applications. It also discusses the potential role of wettability alteration by the polymer and secondary-vs.-tertiary polymer-flooding effects.