## 3 Wettability Alteration  
### Injection of Low-Salinity Water  
The study of rock wettability alteration, particularly in the context of hydrocarbon reservoirs, represents a key aspect in the field of enhanced oil recovery (EOR). For instance, the analysis of the wettability of carbonate rocks is of particular importance, given their strong oil-wet characteristics. These changes can significantly impact the efficiency of oil extraction processes, such as water flooding and injections of saline solutions or CO\({}_{2}\). One of the intriguing aspects in this field is the effect of low-salinity water flooding (LSWF), which has become a focus of active research. Some experimental studies have demonstrated that changes in the composition and salinity of water can positively influence oil recovery from carbonate rocks. However, the underlying mechanisms of this effect remain unclear [39; 40]. [PERSON] et al. conducted experiments to study the behavior of oil droplets on the surfaces of limestone and dolomite in various salt solutions [41]. Their results indicate that in formation water (FW), the shape of oil droplets stabilizes over time, reaching an equilibrium state where the contact angle remains constant. When switching to seawater  
Figure 11: Correlations between various wettability indices for the carbonate samples: (**A**) \(I_{USBM}\) vs. \(I_{AH}\); (**B**) \(I_{AH}\) vs. \(I_{ML}\); (**C**) \(I_{USBM}\) vs. \(I_{ML}\); (**D**) \(I_{L}\) vs. \(I_{ML}\); (**E**) \(I_{AH}\) vs. \(I_{L}\); (**F**) \(I_{USBM}\) vs. \(I_{L}\)[37]. (SW), after 40 h, the contact angles for the oil droplets on both limestone and dolomite decreased by approximately 5-17 degrees. This is illustrated in Figure 12.  
[PERSON] and [PERSON] [41] conducted a study revealing that a decrease in water salinity leads to increased permeability in sandstone formations and improved oil recovery. In their work, [PERSON] et al. [42] noted an increase in oil recovery when using low-salinity water (LSW) for injection. They experimented by varying the salinity of water from 0 to 17,400 mg/L in oil-saturated sandstones, using mica sheets. Changes in the mica's wettability angle suggest a possible influence of low-salinity water on its wettability. Figure 13 shows images of the contact angles of crude oil on mica in various brines at a pressure of 1000 psi and a temperature of 212 \({}^{\circ}\)F.  
Recent studies on the process of spontaneous water injection with varying salinities have shown that both the imbibition rate and ultimate oil recovery are higher when using LSW [43; 44]. According to the authors, changes in salinity may play a key role in altering the wettability of sandstone formations under the influence of LSW, particularly when clay components dictate oil wettability. Figure 12: The contact angle of oil droplets on limestone at high salinities of FW and SW. \(L_{1}\) and \(L_{2}\) represent the diameters of the droplets, which decrease as the contact angle increases [39]. Figure 13: Images of the contact angles of crude oil on mica in various brines at a pressure of 1000 psi and a temperature of 212 \({}^{\circ}\)F. These images are magnified, with actual dimensions of 4.5 \(\pm\) 0.5 mm by 4.5 \(\pm\) 0.5 mm [42]. The mechanisms of wettability alteration are crucial for understanding the effectiveness of LSWF in carbonate and sandstone reservoirs. Despite the growing interest in this topic, significant disagreements remain regarding the underlying mechanisms. [PERSON] et al. suggest that wettability changes may be a dominant mechanism, yet their quantitative impact on increased oil recovery remains unclear [40]. To quantitatively assess the impact of low-salinity waterflooding on rock wettability and enhanced oil recovery, a series of tests were conducted using a petroleum product on clay-free Berea sandstone samples. The experimental results confirmed a slight shift in wettability toward more favorable conditions with decreasing water salinity [40]. [PERSON] et al.