## 3 Nanoparticles in EOR
### Silica-Based
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**NP Type** & **Surface Coating** & \begin{tabular}{c} **Concentration** \\ **(wt \%)** \\ \end{tabular} & \begin{tabular}{c} **Influencing** \\ **Factor** \\ \end{tabular} & \begin{tabular}{c} **Emulsion/Foam** \\ **Type** \\ \end{tabular} & **References** \\ \hline SiO\({}_{2}\) & \begin{tabular}{c} Hydrophilic \\ Hydrophobic \\ \end{tabular} & 0.05–5 & NP wettability & \begin{tabular}{c} decane-in-water \\ water-in-decane \\ \end{tabular} & [95] \\ \hline Fumed SiO\({}_{2}\) & Neutral-wet & 0.1–5 & Concentration & W/O or O/W & [96] \\ \hline Polystyrene & Carboxy-coated & 2 & Brine salinity & W/O or O/W & [97] \\ \hline SiO\({}_{2}\) & Different SiOH & 1 & SiOH coverage & CO\({}_{2}\)-in-water & [98] \\ \hline SiO\({}_{2}\) & Silylating agent & 0.9–2.4 & CO\({}_{2}\) density & Water-in-CO\({}_{2}\) & [99] \\ \hline SiO\({}_{2}\) & \begin{tabular}{c} Hexadecyltrimethoxysilane \\ and polyvinyl alcohol \\ \end{tabular} & 3 & - & O/W & [100] \\ \hline SiO\({}_{2}\) & \begin{tabular}{c} sodium dodecyl sulfate \\ and cetyl trimethyl \\ ammonium bromide \\ \end{tabular} & 0.1–0.5 & Concentration, surfactant & O/W & [101] \\ \hline SiO\({}_{2}\) & \begin{tabular}{c} Hydrophilic \\ Partially hydrophobic \\ \end{tabular} & 1 & NP type & O/W & [102] \\ \hline SiO\({}_{2}\), clay & \begin{tabular}{c} Alpha-olefin sulfonate, \\ sodium dodecyl sulfate \\ and betaine \\ \end{tabular} & 500 ppm & \begin{tabular}{c} Surfactant, NP \\ type \\ \end{tabular} & CO\({}_{2}\)-in-water & [103] \\ \hline AlOOH & \begin{tabular}{c} Sodium cumenesulfonate \\ (SC) \\ \end{tabular} & 1 & \begin{tabular}{c} SC \\ concentration \\ \end{tabular} & CO\({}_{2}\)-in-water & [104] \\ \hline SiO\({}_{2}\) & Partially hydrophobic & 0–2 & Surfactant & Gas-in-water & [105] \\ \hline AlOOH & Sodium dodecyl sulfate & 1 & Surfactant & N\({}_{2}\)-in-water & [106] \\ \hline SiO\({}_{2}\) & Three wetting states & 5000 ppm & \
\begin{tabular}{c} NP wetting \\ state \\ \end{tabular} & CO\({}_{2}\)-in-water & [107] \\ \hline SiO\({}_{2}\) & Hydrophilic & 0.5 &
\begin{tabular}{c} Four \\ surfactants \\ \end{tabular} & CO\({}_{2}\)-in-water & [108] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of the reported experimental studies on nanoemulsion and nano-foam. injection scenario [82]. For application in heavy oil recovery, silica NPs dispersed in brine in a carbonate core sample improved recovery by 39% to 61% [93]. A combination of silica NPs with a polymer for EOR was also studied. [PERSON] et al. [112] dispersed silica NP into a polymer (polyacrylamideamide) solution in a glass micromodel to study the rheology of a polyacrylamide solution when silica NPs are present in the mixture. By applying 0.1 wt % of silica NP to the mixture, the pseudo-plasticity of the polymer solution was improved at a low shear rate and the overall viscosity of the mixture increased, which led to up to 10% additional oil recovery. [PERSON] et al. [88] studied the utilization of silica NPs dispersed in a polymer and surfactant mixture for chemical EOR and found that silica NPs could lower and stabilize the interfacial tension for a Pickering emulsion, leading to 21% additional recovery compared to conventional surfactant-polymer flooding. The efficiency of a conventional polymer and surfactant-polymer flood is reduced when the temperature increases. By contrast, the nanofluid mixture exhibits stable behavior at higher temperatures, making it a potential solution for high-temperature chemical EOR [113; 114]. Several problems such as viscous fingering, channeling, and poor sweep efficiency are often experienced during conventional CO\({}_{2}\) flooding [115]. Therefore, the formation of a CO\({}_{2}\)-in-water foam was proposed to handle those problems [116]. [PERSON] et al. [117] investigated the effect of hydrophobic silica NP in CO\({}_{2}\)-water foam by varying the size and concentration of NPs.