## 4 Conclusions  
In this research, a systematic screening study was carried out to screen surfactants, alkalis, and NPs for Field A and assess their flooding performance on the core scale. Caspian seawater was chosen as makeup brine for all chemical solutions as it has been used for waterflooding in the field for years. Surfactant screening demonstrated that surfactant solution (with co-surfactant) was able to generate microemulsion and lower oil-water IFT. Particularly, anionic surfactant 2S in combination with co-surfactant 2A with a 2S/2A ratio of 30/70 and an overall concentration of 1.5 wt% successfully produced Winsor Type III microemulsion and resulted in a two order of magnitude reduction in IFT, lowering it from 14 mN/m to 0.2 mN/m. The screened surfactant was tested for adsorption control with alkalis NaOH and Na\({}_{2}\)CO\({}_{3}\) and SiO\({}_{2}\) NPs. Both static and dynamic adsorption results showed a better performance of 0.02 wt% Na\({}_{2}\)CO\({}_{3}\) as it caused a 21% and 9% reduction  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Test Type**} & \multirow{2}{*}{**Injection Stage**} & \multicolumn{2}{c}{**Recovery Factor**} & \multicolumn{2}{c}{**Incremental RF**} \\ \cline{3-5}  & & **(\%OOIP)** & **(\%OOIP)** & **(\%ROIC)** \\ \hline \multirow{2}{*}{Surfactant Flooding} & SW & 42.9 & - & \\  & Surfactant & 59.8 & 16.9 & 29.6 \\ \hline Alkali–Surfactant & SW & 41.0 & - & - \\ Flooding & Alkali–Surfactant & 53.5 & 12.6 & 21.3 \\ \hline NP–Surfactant & SW & 40.5 & - & - \\ Flooding & NP–Surfactant & 62.5 & 22.0 & 37.0 \\ \hline \hline \end{tabular}
\end{table}
Table 10: Comparison of oil recovery factors by ASP and NSP flooding.  
in surfactant static and dynamic adsorption, respectively. NPs, however, did not provide favorable adsorption control. To test the screened chemicals in terms of oil recovery efficiency, three coreflood tests were performed utilizing surfactant, alkali-surfactant, and NP-surfactant.  
The coreflood study showed that the selected formulations were able to recover the residual oil by the combined action of surfactant and alkali/NPs. However, the NPs performed better in that they effectively lowered surfactant adsorption as well as aided in IFT reduction. Surfactant loss was minimized and an appreciable microemulsion volume was generated by the NP-surfactant solution. Thus, residual oil was effectively mobilized by the injected chemicals, notably reducing S\({}_{\text{or}}\). The incremental oil recovery by NSF was 9% higher compared to ASF. The results of this study showed that each constituent in a chemical flood design must be carefully and thoroughly evaluated as the recovery of the residual oil is strongly affected by the combined and individual actions of the chemicals involved. Based on the superior performance of alkali in lowering surfactant adsorption and a higher residual oil recovery by NSF flooding, an effective chemical flooding recipe can be designed by combining the chemicals selected in this study with an optimum polymer for Field A.  
Conceptualization, A.D., A.M. and D.S.; methodology, A.D. and M.S.; validation, M.S., P.P. and D.M.; writing--original draft preparation, A.D., A.M. and D.S.; review and editing, M.S. and P.P.; supervision, M.S., P.P. and D.M. All authors have read and agreed to the published version of the manuscript.  
This research was funded by \"Samruk-Kazyna\" grant number SMG2022003, and The APC was funded by SMG2022003.  
Not applicable.  
The authors thank \"Samruk-Kazyna\" JSC, KMG Engineering, and Nazarbayev University for supporting this research.  
The authors declare no conflict of interest.