Experimental Investigation of Amine-Surfactant CO₂ Foam Stability Enhanced by Silica Nanoparticles

The CO₂ foam generated by the conventional surfactants usually does not show long-term stability due to the substantial solubility and diffusivity of CO₂ in water. Silica nanoparticles with different wettability and high adsorption energy on the gas–water interface can be used as a stabilizer to enhance the stability of the CO₂ foam. In this study, nine kinds of nonionic amine surfactants were employed to generate the CO₂ foam, while three kinds of silica nanoparticles were selected and added to improve the CO₂ foam stability. The influences of various factors, including pressure, temperature, pH, surfactant, and nanoparticle, on the CO₂ foam stability have been investigated. The experimental results show that without nanoparticles, the CO₂ foam stability decreases with the increase of the number of EO groups in the ethoxylated amine surfactant, especially under high-temperature and high-pressure (HTHP) conditions. In general, the nanoparticles with a low concentration (<0.5 wt %) have little influence on the CO₂ foam stability, but when the concentration of nanoparticle is enhanced high enough (1.0 wt %), the CO₂ foam stability can be improved significantly. In particular, by adding 1.0 wt % nanoparticle of QS-150 to 0.5 wt % surfactant of C₁₈N(EO)_2/10, the CO₂ foam stability has been increased 5–6 times, while the volume of generated CO₂ foam has been increased by 17–31%. Therefore, in this study, the synergetic mechanisms between the amine surfactants and the silica nanoparticles to generate and stabilize CO₂ foam have been identified.