Is wettability alteration the solo recovery mechanism for microscopic oil recovery during polymer EOR?

Polymer flooding is one of the most applied enhanced oil recovery (EOR) method employed to improve the oil recovery rate in a depleted reservoir. The prime purpose of polymer is to increase the viscosity of the injection fluids so that it provides adequate mobility control with the resident oil. In other words, polymer solution when propagating at the reduced mobility tends to contact more oil and therefore results in an increased displacement sweep, thus improving the oil recovery. Polymer flood also contributes to improvement in macroscopic sweep efficiency by overcoming vertical stratification. In recent times, polymer with significant elastic characteristics were reported to cause an increase in microscopic displacement efficiency (Clarke et al. 2016; Azad and Trivedi 2020; 2021; Ehrenfred 2013; Qi et al. 2017; Erinick et al. 2018). Polymers influence on displacement efficiency and the underlying mechanisms associated with it is a debated topic (Clarke et al. 2016; Seright 2017; Azad and Trivedi 2019; Li et al. 2020). While the sweep efficiency, the well-known EOR recovery mechanism and injectivity are correlated with the pressure drop (Azad and Trivedi 2020; Green and Willhite 2017), the polymers ability to lower the residual oil saturation (Sor)occurring at low flux fails to get correlated with the pressure drop (Clarke et al. 2016; Qi et al. 2017; Erinick et al. 2018; Azad and Trivedi 2020 Azad and Trivedi 2021). What causes the additional oil recovery? Wettability alteration has been considered as the main reason for additional Sor reduction (Seright 2017; Li et al. 2020). While wettability alteration is the main microscopic recovery mechanism during other EOR methods (Azad 2021), would it be the only mechanism during polymer EOR? This question arises because polymer with limited elastic characteristic were not reported to show an increase in microscopic displacement efficiency (Clarke et al. 2015; Qi et al. 2017; Erinick et al. 2018). Does that mean viscoelasticity is related to polymers wettability alteration? Or, wettability alteration by itself is not a significant parameter and it need to be synergised with polymers elasticity to provide a microscopic influence? These important questions still remain to be addressed in evaluating effectiveness of polymer flooding (Clarke et al. 2016; Seright 2017; Erinick et al. 2018; Li et al. 2020; Seright and Brattekas 2021). This proposed research will help in answering these questions.