# Preparation of Modified Colloidal Gas Aphrons and Analysis of the Oil Displacement Effect
## 3 Results and Discussion  
### Selection of the Foaming Agents  
To optimize the foaming agent, the selected surfactants included anionic, cationic, and nonionic surfactants. The foaming properties of different CGA systems prepared by adding various modifiers were compared. SDBS, SDS, OP-10, Tween-20, CTAB, and SYHSY were all obtained from Sinopharm Chemical Reagent Co., Ltd. The experiments were conducted at 15 \({}^{\circ}\)C, with a stirring time of 4 min and speed of 8000 rpm, to study the foaming volume and half-life period of SDBS, SDS, OP-10, Tween-20, Tween-80, and SYHSY at a concentration of 5 g/L, and the results are shown in Figure 2.  
The results indicated that the addition of SDS solution attained the largest foam volume, almost 580 mL, followed by OP-10 at 455 mL, and the foam volume when using Tween-80 was the smallest at 290 mL. SDS also had the maximum half-life period, almost 9 min. The half-life period of the similar surfactant SYHSY was relatively shorter, close to 7 min, and that of OP-10 and SDBS was approximately 5 min. In this study, validation experiments were also conducted. CGA (610 mL) was  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Oil** & **Void** & **Water Phase** & **Porosity** & **Oil** \\
**Item** & **Displacement** & **Volume** & **Permeability** & **(\%)** & **Saturation** \\  & **System** & **(mL)** & **(\(\upmu\)m\({}^{2}\))** & **(\%)** & **(\%)** \\ \hline Sandpack cylinder 1 & Water flooding & 64.7 & 2.15 & 29.6 & 88.3 \\ Sandpack cylinder 2 & CGA flooding & 64.5 & 2.14 & 29.5 & 88.2 \\ Sandpack cylinder 3 & Modified CGA flooding & 64.6 & 2.13 & 29.6 & 88.3 \\ \hline \hline \end{tabular} For Table 1, the preparation procedure of the saturated sandpack and the measurement procedures for the sandpack properties were as follows: 100–300 mesh quartz sand was accurately filled to a height of 30.11 cm in a cylinder with a cross-sectional area of 7.25 cm\({}^{2}\), and, during filling, the sand column was regularly compacted with a hammer. The cylinder was weighed after completion of quartz sand filling, and then the sandpack was saturated with water in a vacuum until completely saturated. Thereafter, the cylinder was weighed again, and the pore volume and porosity were calculated, while the water injection pressure difference was measured at a speed of 9.8 mL/min. According to the equation, \(\mathrm{K_{W}=Q_{N}+L(A\times 2P)\times 10^{-9}}\), the permeability of the water phase was calculated. Oil was injected into the sandpack cylinder saturated with water, where the volume of displaced water represents the void volume filled with oil, which is the oil saturation.  
\end{table}
Table 1: Parameters of the sandpack cylinders in the oil displacement experiments. CGA-colloidal gas aphron.  
Figure 2: Effects of the different foaming agents on the foam volume and half-life period of the modified CGAs: (**a**) foam volume; (**b**) half-life period.  
obtained by adding 5 g of SDS foaming agent to 100 mL of water at 15 \({}^{\circ}\)C, stirring for 3 min at a speed of 8000 rpm. The bubble diameter range of the system was 0.5-20 \(\upmu\)m, and the average diameter was 5.7 \(\upmu\)m. The results were basically consistent with the literature [9].