2.1 and SAP-AP1 # 2.2.

**5. Water-to-oil ratio**

The ratio of remaining to initial oil saturation as a function of volume of fluid injected and injection step is presented in **Figure 5** for the baseline polymer and SAP-AP1 system.

**Figure 4.** Percentage of cumulative oil recovery versus volume of fluid injected and flooding stage: (a) Baseline # 1.1 and SAP-AP1 # 1.2 and (b) Baseline # 2.1 and SAP-AP1 # 2.2.

**Figure 5.** *S*ro/*S*oi versus volume of fluid injected and flooding stage: (a) Baseline # 1.1 and SAP-AP1 # 1.2 and (b) Baseline # 2.1 and SAP-AP1 # 2.2.

**Figure 5** clearly shows the effect of each of the flooding stages on oil recovery. The polymer flooding stage produced a dramatic decrease of the *S*ro/*S*oi ratio that rapidly stabilized during the post-polymer waterflooding stage. The average *S*ro/*S*oi ratio obtained from the Baseline tests # 1.1 and # 2.1 was 0.33, while the average *S*ro/*S*oi ratio attained from the SAP-AP1 tests # 1.2 and # 2.2 was 0.14.

These experimental results demonstrate that the optimum SAP-AP1 system provided a more efficient mobility control compared to the baseline AP1, which resulted in a more stable viscous displacement and accelerated heavy oil recovery. Furthermore, the low concentration of anionic surfactant contained in the SAP-AP1 formulation reduces the interfacial tension (IFT) of the oilbrine system from 30 [45] to 0.032 dynes/cm. This remarkable reduction in IFT decreases capillary forces, which facilitates the detachment and mobilization of oil during SAP-AP1 flooding [46, 47]. Therefore, the SAP-AP1 system produces incremental oil recovery by the synergistic effect of greater mobility control functionality and by decreasing the IFT of the oil-brine system.
