## 3 Results and Discussion
### Results of the Core Flooding Test  
The high reactivity of the powdered samples used in the flotation test suggests that they yielded results more rapidly than the interaction with actual rock samples during the fluid flow processes. Therefore, to confirm the influence of the reaction time more accurately, core flooding experiments were conducted with varying reaction times, along with examining the wettability improvement of nanoparticles, oil recovery, and changes in the properties of rock particles. Waterflooding, nanofluid injection, and post-waterflooding of 3, 1, and 3 of PV, respectively, were performed after a controlled reaction time. Figure 9 shows the recovery and pressure drop across the core before and after PVI when the reaction time was 12 h. The oil recovery increased by approximately 45% during the waterflooding period, with an additional 10% increase in the remaining intervals. Among the series of injections, the pressure changes were found to stabilize within 20 psi, and the pressure drop in the later interval gradually increased. Moreover, it can be observed that the pressure difference between the early and late stages is not significant. The change in permeability before and after nanofluid injection was minimal; however, the increase in the recovery rate was also modest, indicating an inefficiency. Furthermore, the contact angle decreased slightly from 134.8\({}^{\circ}\) to 125.1\({}^{\circ}\) before and after the nanofluid reaction. The extent of this change was not substantial and was still ineffective in altering the wettability in an oil-wet state. When the reaction time was 24 h, a pronounced increase in the recovery rate was observed (Figure 10). The stable pressure levels before and after waterflooding in the field increased from approximately 30 psi to 50 psi; however, the pressure difference was not significant. During the waterflooding period, 54.1% of the oil was recovered, followed by an additional 7.1% during the subsequent nanofluid injection. After the nanofluid reaction, 18.7% was recovered during the post-waterflooding period. It was confirmed that 25.8% in total was recovered by applying EOR methods after the waterflooding phase. The contact angle significantly decreased from 166.5\({}^{\circ}\) to 43.4\({}^{\circ}\), demonstrating a substantial shift from strong oil-wet conditions to strong water-wet conditions on the surface. Figure 8: Effect of treatment temperature on flotation test results. For a reaction time of 48 h, an additional oil recovery of 12.6% was confirmed after the waterflooding period, and the stable pressure levels before and after waterflooding in the field increased by approximately twofold, from 10 psi to 20 psi (Figure 11). The contact angle significantly decreased from 165.4\({}^{\circ}\) to 62.4\({}^{\circ}\), indicating a substantial shift from strong oil-wet conditions to strong water-wet conditions on the surface. At a reaction time of 72 h, the additional recovery rate was less than 10%, indicating a reduced increase in the recovery rate, as shown in Figure 12. In the water-flooding section, the pressure was approximately 23 psi; however, in post-waterflooding, the pressure did not stabilize and continued to increase throughout the injection of 3 PV. This indicates that nanoparticle aggregation was generated in the core plug by long-term exposure to nanofluids at high temperatures. In addition, it suggests that the reaction time is a sensitive parameter for altering rock properties such as wettability and permeability. The contact angle significantly decreased from 166.5\({}^{\circ}\) to 43.4\({}^{\circ}\), confirming a substantial shift from strong oil-wet conditions to strong water-wet conditions on the surface.