Effect of pH on silica nanoparticle-stabilized foam for enhanced oil recovery using carboxylate-based extended surfactants

Alkyl-carboxylate extended surfactants as foaming agents have been formulated to generate stable nanoparticle-surfactant foam systems. Because of their unique characteristics, these extended surfactant contains a carboxylate head group and together with ethylene oxide groups inserted between the alkyl tail and carboxylate head group. They tend to outperform with a low precipitation tendency at high brine conditions, which is an excellent property for enhanced oil recovery (EOR) applications. Interestingly, the solution pH is a factor affecting the carboxylate surfactant's properties relating to change in the foam characteristics. In this study, the impacts of varying pH from 3 to 11 of the surfactant systems (0.5 wt%) with and without the presence of 100 ppm silica nanoparticles (SNPs) on the foam behavior were evaluated and discussed in terms of foamability, foam stability, apparent rates of liquid drainage, foam bubble size, and bubble size distribution at room temperature (25 +/- 2 degrees C). For a continuous-feed sand pack column, the foam system with the SNPs at pH of 9 had the highest foam stability as a result of the largest foam film thickness (102 mu m) and the smallest bubble size (333 mu m). This condition also resulted in the highest crude oil recovery, accounted for 53.8% of the oil recovery by foam flooding and about 96.3% in the total oil recovery. In addition, the carboxylate extended surfactant systems with SNPs showed a noteworthy result of lower adsorption onto Ottawa sand compared with the system without added SNPs at the same pH value due to the competitive adsorption onto the SNPs and sand surface. This led to the reduction in surfactant losses onto the sand, which is highly beneficial for surfactant foam flooding in enhanced oil recovery process.