## 3 Results and Discussion
### Chemicals Screening
#### 3.1.4 Dynamic Adsorption Results  
Figure 12 illustrates the relationship between pressure drop and injected pore volumes for all three tests. The observed pressure drop behavior suggests that there is relatively lower surfactant adsorption during alkali-surfactant flooding when compared to the other  
Figure 11: Comparison of alkalis and NPs in reducing surfactant adsorption after 72 h.  
Figure 10: Effect of silica NPs on surfactant adsorption after 72 h of aging time.  
two cases. Notably, from Figure 12, it is evident that the pressure drop during NP-surfactant flooding was approximately 67% higher than the pressure drop during alkali-surfactant flooding. Such a high pressure drop could be due to pore blocking caused by the NPs. Moreover, it can be observed in Figure 12b that the pressure drop during alkali-surfactant flooding was lower than the SW pre-flush pressure drop.  
This lower pressure drop during alkali-surfactant flooding may be due to presence of a greater number of surfactant molecules in the SW imparting a lower in situ viscosity and yielding a lower pressure drop. The viscosity of the surfactant solution at 63 \({}^{\circ}\)C was 0.75 cp while the viscosity of seawater was 0.79 cp. Thus, a lower pressure drop during alkali-surfactant flooding is an indication of less surfactant adsorption.  
The surfactant concentration In the effluents during surfactant flooding and seawater post-flush was measured using a spectrophotometer and was plotted as a function of pore volume injected, as shown in Figure 13.  
Figure 12: Pressure drop profile during dynamic adsorption test of (**a**) surfactant, (**b**) alkali-surfactant, and (**c**) NP–surfactant.  
It can be observed that the mass of surfactant recovered during NP-surfactant flooding was less than the mass recovered during alkali-surfactant flooding. Dynamic surfactant adsorption was calculated using Equation (1) and the results are presented in Table 9.  
The standalone surfactant dynamic adsorption was around 9.2 mg per gram of rock. Dynamic adsorption is generally less than static adsorption and yields more realistic results under filed conditions. The results in Table 9 show that alkali resulted in a 9% reduction in the surfactant dynamic adsorption. Silica NPs, on the other hand, lowered the dynamic adsorption by only 1%. These results indicate that the addition of alkali to surfactant solution can improve surfactant performance by lowering its adsorption. The reduction in surfactant adsorption is attributed to alkali, such as sodium carbonate, dissociating into a weak carbonic acid and generating OH\({}^{-}\) ions upon interaction with water molecules. As a result, the system's pH increases, leading to a more negatively charged surface of the sample. Consequently, there is an electrostatic repulsion between the surfactant molecules and the rock surface, significantly decreasing surfactant adsorption [50].  
NPs, however, were not successful in overcoming the surfactant adsorption issue. Due to the anionic surfactant charge not being negative enough in the presence of NPs, the repulsive force between the rock and the surfactant molecules weakened, resulting in a higher surfactant dynamic adsorption. The outcomes of the dynamic adsorption study unequivocally validated the appropriateness of Na\({}_{2}\)CO\({}_{3}\) for controlling 2S/2A adsorption on the Field A rock surface. Consequently, based on the findings from both the static and dynamic adsorption experiments, Na\({}_{2}\)CO\({}_{3}\) was selected as an ingredient in the surfactant solution recipe for Field A ASP design to reduce surfactant adsorption. Following the dynamic adsorption tests, the chosen alkali and NPs were evaluated for their impact on the microemulsion generation capacity of the surfactant.