# Flow Dynamics of Sulfate-Modified Water/Polymer Flooding in Micromodels with Modified Wettability
## 3 Results and Discussion
### Microfluidics-Oil Recovery and Pressure Response for Secondary Mode Brine Flood  
#### 3.2.1 Oil-Wet Artificial Model  
SSW injection was performed as the base case, and SSW flooding was repeated in the cleaned model to observe the reproducibility of the oil recovery data. From Figure 7, the main flooding was a straight flow path between the injection and production points. Figure 8 shows oil recovery and pressure data for SSW flooding. Looking at the pressure response and final RFs, similar values are observed for both experiments. For further investigation into the effect of brine composition on oil recovery, three injection brines of Table 2 were flooded in the secondary mode. Figure 9 describes RF profiles and pressure responses for the four injection brines. Table 9 summarizes further details with regards to additional oil recovery with modified brines flooding (compared to the SSW injection). Figure 6: Micromodel with different wettability conditions. Lefteach wettability condition represents the micromodel; right zoomed image of the bottom right corner for each micromodel. Figure 7: Artificial structure oil-wet micromodels used for synthetic seawater (SSW) flooding. SSW-1/SSW-2 represents the oil initialization, while BF-1/BF-2 represents after 10 PV injected brine. The slightly higher additional oil recovery from brine (3-5 from Table 9) flooding, compared to SSW injection was due to the fluid-fluid interfacial interaction developed between the oil and brine. The main reason for this could be a negligible local wettability alteration (rock-fluid interaction) of the micromodel established by injected brines. Sulfate-modified water and DSSW do not show a significant impact on the oil recovery. Figure 8: Oil recovery and pressure drop versus PV injected for artificial structure oil-wet micromodel. SSW injection is performed as the secondary mode for both flooding experiments. Figure 9: Oil recovery and pressure drop versus PV injected for artificial structure oil-wet micromodel. Four injection brines of Table 2 are flooded as the secondary mode. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Experiment**} & \multirow{2}{*}{**Flooding Brine**} & **Soi** & **Swc** & **RF** & **Additional RF** \\ \cline{3-5}  & & & & **(\%)** & \\ \hline
1 & SSW & 85.02 & 14.98 & 32.84 & - \\
2 & SSW & 83.44 & 16.56 & 32.38 & - \\
3 & SSW+2 SO42\({}^{-}\) & 85.13 & 14.87 & 35.01 & 2.63 \\
4 & SSW-Na & 85.64 & 14.36 & 33.66 & 1.27 \\
5 & DSSW & 83.48 & 16.52 & 34.84 & 2.46 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Summary of artificial structure oil-wet micromodel with initial oil saturation, connate water saturation and final oil recovery factor. strong ability to disturb the hydrophobic layer coated on the matrix of the micromodel for wettability alteration. It is believed that this additional oil recovery was obtained due to the improved ionic interfacial response at the interface (fluid-fluid interaction). This ionic interfacial interaction developed due to a slight increase in the static IFT at the interface between the modified brines and the oleic phase. Further, the concept of PDI/non-PDI ions for SSW-Na brine flood did not work as expected, and produced only 1.27% additional oil. Hence, this indicates that adding/removing the PDI/non-PDI ions works, focusing on the concept of wettability alteration as a main recovery mechanism. Considering the economic aspect of the project, sulfate-modified (SSW+2 SO42) injection was found to be a suitable brine when comparing the extra oil recovery and brine preparation (the removal of NaCl from SSW or dilution of the SSW). Figure 10 is the final image after \(\approx\)10 PV brine flood (Table 9 injection brine). Table 9 describes the initial oil saturation and connate water saturation, which fall in the same range. RF represents the final RF after 10 PV injected. Further, additional oil RF represents the additional oil produced after brine flood compared to SSW.