## 3 Results and Discussion
### Polymer Flooding in Oil-Saturated Micromodel  
Polymer solutions (prepared in SW) with varying amounts of sulfates were flooded in oil-saturated micromodels. The approach helped understanding which factor between salinity and hardness has a dominating impact on in situ polymer shear viscosity. Polymer flooding in oil-saturated micromodel is perform at a seemly reservoir (field scale) injection flux of 1 ft,/day. As previously shown, Figures 7 and 8 depicted 1 ft,/day fall within the range of shear-thinning behavior of polymer solutions. Therefore, flooding experiments in micromodels were used to evaluate polymer shear analysis in porous media and to investigate the impact of salinity and hardness. Under the assumption (previously demonstrated), that viscoelasticity mainly dominates at higher flux values around injection and production wells, experiments performed in micromodels were analyzed by using the shear viscosity approach part (low flux). In situ shear rate (apparent shear rate) was calculated by using two approaches at the flux rate of 1 ft,/day, presented in Table 5. Determining a maximum and minimum shear rate range helped in defining the diagonal areal variation of the flooding path between injection and production points (or inlet bottom-left and outlet top-right), as shown  
Figure 12: Apparent extensional (elongational) viscosity as a function of apparent extensional rate for polymer solutions before core flood (B) and after core flood (A), at 22 and 55 \({}^{\circ}\)C, prepared with reservoir brine and synthetic seawater. in Figure 3 The lower in situ shear rate value is in line with the low flux values of Figure 7; hence, it demonstrated the prevalence of the shear flow of polymer solutions in porous media. Polymer flooding (2000 ppm prepared in B1 and B3) was performed in oil-saturated micromodels with initial water saturation. Table 6 summarizes the initial oil and water saturations before brine/polymer flooding. Almost the same values of initial saturation were achieved and can be seen in Table 6. Oil recovery factor and pressure profiles obtained for SW flooding (used as a benchmark) and both polymer solutions can be seen in Figure 13.  
Seawater (SW), B1, produced the minimum oil recovered of 33% with lowest and stable pressure response. However, as expected, higher recoveries from both polymer solutions can be clearly seen in Figure 13. Moreover, polymer prepared in SW produced 4% additional oil recovery as compared to the polymer prepared in SW+4S (B3). Oil recovery experiments are in line with results obtained in in a previous study [4; 6]. Increasing the amount of sodium sulfate in brine increases the polymer sensitivity to mechanical degradation. Even though SW has higher hardness (\(R^{+1}=0.13\)) as compared to SW+4S (\(R^{+1}=0.09\)), an increased amount of TDS depicted a stronger impact compared to hardness. The reason behind this is the excessive amount of sodium ions in SW+4S. Positive sodium ions \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Experiment** & **Soi \({}^{\star}\)** & **Swi \({}^{\star\star}\)** & **Porosity** & **Permeability (B)** & **PV \({}^{\star\star}\)** & **RF \({}^{\star\star\star}\)** \\ \hline  & **\%** & **\%** & **\%** & **D** & **\(\mu\)L** & **\%** \\ \hline SSW & 81.28 & 18.72 & 27 & 13 & 22 & 33 \\ SSW-P & 79.98 & 20.02 & 27 & 13 & 22 & 56 \\ SSW+4S-P & 80.37 & 19.62 & 27 & 13 & 22 & 52 \\ \hline \hline \end{tabular}  
\({}^{\star}\) = Initial oil saturation, Swi \({}^{\star\star}\) = Initial water saturation, PV \({}^{\star\star\star}\) = Pore volume and RF \({}^{\star\star\star}\) = Recovery factor.  
\end{table} 
Table 6: Summary of micromodels initialization and oil recovery factors at 22 \({}^{\circ}\)C.  
Figure 13: Oil recovery factor/pressure drop as a function of pore volume (PV) injected in micromodel at 22 \({}^{\circ}\)C. Synthetic seawater and diluted polymer solutions injection is performed as the secondary mode. reacted with the negative ionic charge on polymer molecules, which in turn reduced the polymer molecular structure.