# Preparation of Modified Colloidal Gas Aphrons and Analysis of the Oil Displacement Effect
## 3 Results and Discussion
### The Performance of the Modified CGA Foam Flooding  
Water flooding, CGA foam flooding, and modified CGA foam flooding were carried out on three sandpack cylinders with similar permeability and oil saturation values (V = 9.5 mL/min). The injection pressure and recovery results are shown in Figure 6.  
The results showed that the injection pressure during water flooding increased over time. After 8 min, the pressure stabilized at approximately 3.1 MPa. Upon increasing oil phase displacement, the pressure gradually decreased; the pressure during CGA flooding and modified CGA flooding reached a peak at 11 and 12 min, respectively, and the oil phase started to be displaced. This phenomenon was related to the pressure accumulation process of foam in the oil zone. The recovery ratio results revealed that the water flooding oil yield was 40.3%, the CGA flooding oil yield was 54.7%, and the modified CGA flooding oil yield reached 63.6%. It is clear that the modified CGA system had a superior recovery effect. In addition, a series of gradient displacement experiments with the same sandpack cylinder were carried out. That is, water flooding was firstly performed, then CGA flooding, and finally modified CGA flooding. The experimental results are summarized in Table 2.  
The data in Table 2 indicate that, for the gradient displacement experiment with the same sandpack cylinder, the recovery ratio was 42.1% by water flooding, 10.7% by CGA flooding, and 16.4% by modified CGA flooding. It can be observed that the CGA flooding recovery was 10.7% on top of that of water flooding, and that the modified CGA flooding recovery was 16.4% relative to that of CGA flooding, indicating that the recovery efficiency of modified CGA flooding was notable. In summary, the displacement experiments with different sandpack cylinders and the gradient displacement experiment with the same sandpack cylinder all demonstrated that the displacement effect of modified CGA flooding was better than that of water and CGA flooding. To further clarify the mechanism, experiments were carried out from two aspects: the interfacial tension between the foam system and mixed crude oil, and the content of _n_-heptane asphaltene in gradient flooding with the same sandpack cylinder. The measurement process of the interfacial tension was as follows: in a constant-temperature vessel, crude oil slowly formed droplets through the tip of the tube that fell into the CGA system or modified CGA system. The interfacial tension was calculated according to the equation, \(\gamma\) = f\(\cdot\)V\(\cdot\)\(\varrho\)-g/R, where V is the measured crude oil volume, \(\varrho\) is the crude oil \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Water Flooding** & **CGA Flooding** & **Modified CGA Flooding** \\ \hline Oil recovery ratio (\%) & 42.1 & 10.7 & 16.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Oil recovery ratio in the gradient displacement mode in the three systems with the same sandpack cylinder. Figure 6: The injection pressure and recovery results: (**a**) injection pressure; (**b**) recovery ratio. density, g is the acceleration due to gravity, R is the emitter radius, and f is a correction factor [15]. The asphaltene content was determined with _n_-heptane as the solvent, and, according to the industry standard method, the relative error was within 3%. The results (Table 3) showed that the interfacial tension of the mixed crude oil and foam system was reduced from 3.29 to 2.68 mN-m\({}^{-1}\) by adding 0.1 g/L modifier GXJ-C to the CGA system. Figure 7 shows the asphaltene content data of the crude oil with different system gradient displacements. The figure reveals that the asphaltene content in the oil recovered by water flooding was 4.66%, and that the asphaltene content in the oil recovered by CGA flooding was slightly lower, at 4.44%. However, the asphaltene content in the oil recovered by modified CGA flooding was 5.48%.