# Ultra-Low Interfacial Tension Foam System for Enhanced Oil Recovery
## 2 Materials and Methods
### Core-Flooding Experiment  
Macroscopic flow characteristics of foam fluid in porous media and the EOR effect of the optimized foam system were investigated by a core-flooding experiment. The parameters of the artificial cores are shown in Table 5, the grouping of the core-flooding experiment is listed in Table 6, the experimental flow chart is shown in Figure 2.  
The core was cylindrical, and the size were 6 cm (length) \(\times\) 2.5 cm (diameter), the volume was 29.45 cm\({}^{3}\). Numbers 1-3 were the high permeability group (\(\approx\)110 mD), numbers 4-6 were the low permeability group (\(\approx\)1 mD).  
Two commonly used chemical flooding methods (i.e., normal foam flooding and alkali-surfactant-polymer (ASP) flooding) were selected as the control groups. All chemical flooding  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number** & **Group** & **Compounding** & **Core** \\ \hline
1 & Normal foam system & 1.5 g/L SDS + 2 g/L PAM & NO.1 \\
2 & ASP & 1 g/L SDBS + 6 g/L Na\({}_{2}\)CO\({}_{3}\) + 1 g/L PAM & NO.2 \\
3 & Target foam system & 1.2 g/L DHPB + 1.8 g/L SDS + 0.075 g/L XC & NO.3 \\
4 & Normal foam system & 1.5 g/L SDS + 2 g/L PAM & NO.4 \\
5 & ASP & 1 g/L SDBS + 6 g/L Na\({}_{2}\)CO\({}_{3}\) + 1 g/L PAM & NO.5 \\
6 & Target foam system & 1.2 g/L DHPB + 1.8 g/L SDS + 0.075 g/L XC & NO.6 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Grouping of the core-flooding experiment.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Symbol** & **Definition** & **Unit** \\ \hline Foaming volume & \(\text{V}_{0}\) & Volume of foam after foaming & mL \\ Residual-liquid volume & \(\text{V}_{\text{t}}\) & Volume of liquid remaining after foaming & mL \\ Foam half-life & \(\text{t}_{\text{t/2}}\) & Time required for the foam’s volume to be reduced by half of its initial volume & min \\ Drainage half-life & \(\text{t}_{0}\) & Time required for the foam to lose half of its liquid & s \\ Foam composite index & FCI & Function of foaming volume and foam half-life & mL-min \\ \hline \hline \end{tabular}
\end{table}
Table 4: Parameters of foaming properties used in this study.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Number** & **Water Permeability (mD)** & **Porosity (\%)** & **Pore Volume (mL)** \\ \hline
1 & 109 & 23.5 & 6.920 \\
2 & 111 & 23.2 & 6.832 \\
3 & 110 & 23.7 & 6.979 \\
4 & 1.2 & 25.7 & 7.568 \\
5 & 1 & 25.9 & 7.627 \\
6 & 1 & 26.1 & 7.686 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Parameters of the artificial cores used in the core flooding experiment.  
processes were conducted after water flooding (water flooding was suspended when the water content of produced fluid was more than 98%).  
A foam generator was used in this section for the foaming process. The foam generator had a set of sieve plates (three layers, 200 mesh, 2 mm spacing) at both the inlet and outlet. N\({}_{2}\) was used as the gas phase of the foam systems. The temperature was maintained by calorstat at 85 \({}^{\circ}\)C, the pressure in the core holder was controlled by back pressure pump at 20 MPa.  
The macroscopic flow characteristics were investigated by the differential pressures at both ends of the core during injection process. The EOR effect was measured by the recovery efficiency of chemical flooding (after water flooding).