## 3 Results and Discussion
### Oil Displacement  
Four core flooding experiments were conducted with different LSW/EW brings. For all experiments, the secondary mode showed a significant recovery factor by seawater injection, but still, a noticeable amount of residual oil remained in the porous media. As an EOR stage, the low salinity water and three options of engineered water were injected. In scenario 1 (injection of 5\(\times\) Diluted CSW), the experiment was held on the core \(\aleph\)1. The recovery factor, pressure difference, and injection rates are presented in Figure 3. Recovery for seawater was identified as 67.51%, and the final recovery has not changed %, which means there is no incremental oil recovery by LSW.  
The core flooding experiment for scenario 2 was held on core \(\aleph\)2. The tertiary stage was implemented by injecting the EW1, ion-tuned water with doubled calcium and sulfate ions concentration (5\(\times\) Diluted CSW with 2 Ca \(*\) 2 SO\({}_{4}\) ions). All results for the second flooding are presented in Figure 4. Recovery for seawater was identified as 72.7%, and no additional recovery was observed by the designed EW with doubled calcium ions.  
The core flooding experiment for scenario 3 was held on core \(\aleph\)3. For this case, the magnesium/sulfate ions concentration was doubled in the engineered water (5\(\times\) Diluted CSW with 2 Mg \(*\) 2 SO\({}_{4}\) ions, EW2) injected after seawater. Results for the third flooding are presented in Figure 5. Recovery for seawater was identified as 74.95%, and with ion-designed water, it reached 76.93%. The additional recovery was 1.98%.  
Figure 2: Change of Potential Determining Ions concentration during aging of an oil-saturated rock (**left**) and a clean rock (**right**) with Low Salinity Water (5\(\times\) Diluted CSW).  
Figure 4: Engineered water (EW1) injection core flooding results (5\(\times\) Diluted CSW with \(2\text{Ca}*2\text{SO}_{4}\) ions).  
Figure 3: Low salinity water injection (5\(\times\) Diluted CSW) core flooding results.  
The core flooding experiment based on scenario 4 was conducted on core N*4. The tertiary stage brine was designed with doubled cations (calcium and magnesium) and sulfate ion (5\(\times\) Diluted CSW with 2 Ca \(*\) 2 Mg \(*\) 2 SO4 ions (EW3). Results of flooding are presented in Figure 6. Recovery for seawater was identified as 66.79%, and with engineered water, it reached 70.15%. The additional recovery was 3.36%.  
Figures 3-6 also show the flow rate (q) and pressure drop (dP) along with the recovery (RF) during the flooding. Each flow rate was maintained until we produced clean water.  
Figure 5: Engineered water (EW2) injection core flooding results (5\(\times\) Diluted CSW with 2 Mg \(*\) 2 SO4 ions).  
Figure 6: Engineered water (EW3) injection core flooding results (5\(\times\) Diluted CSW with 2 Ca \(*\) 2 Mg \(*\) 2 SO4 ions).  
The change in pressure drop occurred due to the increase in the flow rate and alteration in relative permeability by the decrease in the oil saturation in the porous media. A significant pressure drop variation was observed by switching the recovery stages from seawater to low salinity/engineered water. The numerical results for recovery, additional recovery, and remaining oil RF for all 4 cases are presented in Table 5.