## 3 Results and Discussion  
### Contact Angle Measurement and Chromatography Analysis  
All core samples were initially strongly oil-wet. Due to the aging by different LSW/EW designs, wettability was altered to a more water-wet state, which can be observed by the change in the contact angle. Figure 1 shows the difference between initial and changed contact angles for different brines. The changes in the contact angle for diluted Caspian seawater vary from 7.7\({}^{\circ}\) to 13.77\({}^{\circ}\). The change is explained by the surface charge alteration. The sulfate ions are adsorbed on the carbonate surface and replace the negatively charged carboxyl groups. The carboxyl groups leave the surface with positively charged cations, which previously were in the composition of injected brine. This action changes the wettability to a more water-wet state. Figure 1 represents the differences in contact angles by different dilutions of Caspian seawater (LSW) and ion-tuned water (EW). Five times diluted seawater (5\(\times\) Diluted CSW (LSW)) showed the best wettability alteration by dilution, and it is chosen as the optimum dilution for engineered water preparation. By spiking Ca\({}^{2+}\) cation and SO\({}_{4}^{2-}\) anion, a bit higher alteration to the weaker oil-wet state was also observed among engineered water options. The results showed that the activity of cations affects the oil detachment from the rock. These interpretations were based on [PERSON] et al. [13; 38]. In these papers, the role of PDI (potential determining ions) activity in wettability alteration was discussed.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **Rock type** & **Viscosity. cp** & **Acid Number** & **Injection Mode** &
\begin{tabular}{c} **Recovery** \\ **Factor by** \\ **LSW, \%** \\ \end{tabular} \\ \hline [PERSON] et.al [35] & carbonate & 179.2 @20 °C & Not reported & Tertiary & 79\% \\ \hline  & & & & 64\% \\ \hline  & & & & 2\% \\ \hline  & & & & 3\% \\ \hline  & & & & 14\% \\ \hline  & & & & 8\% \\ \hline  & & & & 3\% \\ \hline  & & & & 2\% \\ \hline  & & & & 5\% \\ \hline  & & & & 2\% \\ \hline  & & & & 5\% \\ \hline  & & & & & 2\% \\ \hline  & & & & & 23.50\% \\ \hline \hline  & & & & & \\ \end{tabular}
\end{table}
Table 4: Data reported in the literature for the LSWI to heavy oil formations.  
Figure 1: Contact angle difference by aging with Low Salinity Water/Engineered Water samples.  
The chromatography analysis results are shown in Figure 2. On the graphs, the \(x\)-axis shows the time after the start of the experiment, and the \(y\)-axis is for the concentration ratio (C/C\({}_{0}\)). C is the concentration at a given time t, and C\({}_{0}\) is the initial ion concentration. The figure on the left shows the ions concentration change in 5 times Diluted CSW (LSW) brine during the aging of the oil-saturated pellet. The right figure shows the dynamic ions concentration during the aging of the clean pellet with the same LSW sample. The increase of calcite and sulfate concentrations during the aging of the clean core shows that the rock dissolution mechanism is active. However, the magnesium concentration is stable, which means magnesium is not significantly active during the dissolution. The presence of oil also activated the multi-ion exchange mechanism, confirmed by the adsorption of cations on the rock at later times, as shown in the left figure. Hence, contact angle and chromatography results showed that the well-known mechanisms such as rock dissolution and multi-ions exchange were active, leading to wettability alteration.