Impacts of oil components on the stability of aqueous bulk CO2 foams: An experimental study

Study of foam stability in the presence of oil components is mainly devoted to the impacts of aliphatic components like short- and long-chained alkanes. In this study, several experiments, including critical micelle concentration (CMC) determination, IFT measurement, high pressure bulk foam stability as well as foam texture visualization and analysis have been designed and performed in the presence of various oil solution samples to explore the impacts of aromatic components and compare them with the impacts of aliphatic components on CO2 foam stability. Alpha-Olefin-Sulfonate (AOS) surfactant solutions with different concentrations of surfactant in the presence of various synthetic oil solutions comprising toluene and n-heptane were prepared to compare the interfacial behavior and performance of the surfactant solutions containing aromatic and aliphatic components with regards to foam stability. The results revealed that, due to higher micellar solubilization of the n-heptane as the aliphatic component compared to toluene, surfactant surface activity would be more detrimentally impacted by the presence n-heptane. Employing electrical conductivity measurements, it was observed that the CMC of surfactant solutions with addition of 1 vol% of toluene and n-heptane to the surfactant solution, increased by 15 and 19 times, respectively. Increase in surfactant concentration in solutions above CMC with no oil compound, did not show any promising improvement on foam stability. However, in the presence of different oil additives, increase in surfactant concentration from 0.1 wt% to 0.5 wt% resulted in the increase in foam stability by 45% on average measured by foam half-life time where the foam was generated by aeration method. This observation was further validated by the decrease in IFT, measured by spinning drop method, from the average range of 1.4 mN/m for different oil solutions to 0.6 mN/m by increasing surfactant concentration from 0.1 wt% to 0.5 wt%. IFT measurements between surfactant solutions and different oleic samples with oil components suggested that the presence of higher n-heptane in oil solutions resulted in higher IFT. Similar behavior was observed in foam stability measurements. Generally, addition of oil components to the foam solution resulted in lower foam stability. That is, higher oil content concentration would result in lower foam stability. Also, the presence of n-heptane had more detrimental impacts on foam stability compared to the presence of toluene. The texture of the resulted foam in the presence of toluene and n-heptane was visualized. It was observed that the texture of the foam generated in the presence of toluene had smaller bubble size compared to that in the presence of n-heptane. Also, it was observed that as time passes, oil droplets migrate from lamellae to the plateau borders, resulting in lamellae thinning and foam bubble coarsening and rupture.