The CO2 Foam Stability Enhancement with Switchable Surfactant and Modified Silica Nanoparticles

Abstract

AbstractWhen the silica nanoparticles (NPs) were modified with Glymo silane, the surface charge of NPs would change along with the silane coverage, which has an effect on the interaction with switchable surfactants. This study focused on the electrostatic force between the switchable surfactants and modified silica NPs with different coverage scale. At low pH 4.5, the ethoxylated amine surfactants switched to protonated state with quaternary ammonium group, that contains positive charge. However, when the silane coverage was higher than 1.0 µmol/m2, the mixing solution could keep stable at 80°C due to the fewer negative charge at the NPs surface even in DI water. With increasing the ethylated groups of the switchable surfactant, the solution was more stable, which could be interpreted that the quaternary ammonium with positive charge was hindered by long EO chain. The bulk foam half-life extended twice with adding NPs in the surfactant solution, which proved that the CO2 foam was more stable and when the solution was slightly cloudy, the foam stability enhancement was more obvious, since the NPs more likely adsorbed at the CO2-liquid interface and enhanced the lamella stability at this state. Moreover, after adding NPs, the foam viscosity in sand-pack increased 1.5-2 times, comparing with surfactant alone and depended on the silane coverage of NPs, where the NPs with lower silane coverage have more positive effect on the foam stability enhancement. The mixing formula makes it possible to enhance CO2 foam stability at low pH and given high salinity, which is important to reduce gas mobility in reservoir conditions and, eventually, enhance oil recovery.