# Synthesis of Oligomeric Silicone Surfactant and its Interfacial Properties
## 3 Results and Discussion
### Contact Angle and Surface Energy  
Reservoir grains are hydrophilic in character, but their surface wettability can change from hydrophilic to hydrophobic due to the adsorption of certain surfactants. When the contact angle of water on the rocks is \(<\)90\({}^{\circ}\), the reservoir hydrophilicity is generally better than the lipophilicity, known as water wettability. However, when the contact angle of water is greater than 90\({}^{\circ}\) but smaller than 180\({}^{\circ}\), the reservoir has a stronger lipophilic capability, meaning that the water can only generate adhesional wetting on the reservoir surface rather that immersional wetting, which can only turn a partial gas-solid interface into a solid-liquid surface, known as preferential gas wettability relative to the water. In terms of the condensate gas reservoir, if the reservoir surface wettability changes from hydrophilic to hydrophobic, gas condensate can spread over the surface occupied by gas, allowing it to flow into the wellbore by spontaneous imbibition. Natural cores are the cylindrical rock samples taken from the reservoir by coring, which are the most important, first-hand, and frequently used materials in oil exploration and geology research. Due to the difficulty in obtaining natural cores and their complex components, artificial cores are used in the laboratory experimental evaluation of reservoir research. As the concentration of the surfactant at the solid-liquid interface is higher than the aqueous solution, the wettability can change by the absorption of surfactant in the solution. Table 1 represents the contact angles on the cores and the surface energy of cores versus weight percentage of OSSF at 25 \({}^{\circ}\)C.  
Table 1 describes the weight percentage of OSSF aqueous solutions, showing that when it is higher than 0.20 wt %, the contact angles of water and the surface energy on the surface of the cores adsorbing OSSF are greater than 90\({}^{\circ}\) and less than 30 m/m\({}^{2}\), respectiv  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Cores**} & \multirow{2}{*}{ \begin{tabular}{c} **Weight** \\ **Percentage/wt \%** \\ \end{tabular}  } & \multicolumn{2}{c}{**Contact Angles/\({}^{\circ}\)**} & \multirow{2}{*}{ \begin{tabular}{c} **Dispersion** \\ **Water** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Polar Force** \\ **Force/(mJ/m\({}^{2}\))** \\ \end{tabular}  } & \multirow{2}{*}{\ \begin{tabular}{c} **Surface** \\ **(mJ/m\({}^{2}\))** \\ \end{tabular}  } \\  & & & & & \\ \hline
\begin{tabular}{c} H\(\mathrm{\ddot{a}}\)ian \\ Ying\(\mathrm{\ddot{a}}\)i \\ H\(\mathrm{transfer the cores' surface property from water-wet to preferential gas-wet by decreasing its surface energy. The contact angles of water significantly increase when the mass fraction changes from 0.10 to 0.20 wt %. Accounting for surface inhomogeneities of these cores, when the weight percentage of the OSSF solutions is greater than 0.20 wt %, the contact angles and the surface energy show insignificant change, which means that a higher OSSF weight percentage cannot improve the preferential gas wettability. These results show that mass fraction plays a major rule in wettability alteration and affects the interfacial viscosity and microscopic distribution of oil, gas, and water in the intergranular pores, which in turn alter the fluid flow properties. Figures 8 and 9 show that the contact angles of water on the cores which adsorbed OSSF slowly decline, stabilizing within one minute, which indicates that OSSF absorbed on the cores implied wettability alteration of the cores maintained for a certain period. In the case of Yingxi cores steeped in a 0.50 wt % OSSF solution, the contact angles of water on the cores slowly decline from 114.53 to 109.34\({}^{\circ}\) in a minute time period, whereas Haian cores decline from 110.07 to 106.46\({}^{\circ}\).