Synergistic effects between anionic surfactant SDS and hydrophilic silica nanoparticles in improving foam performance for foam flooding

In foam flooding, foams stabilized by conventional anionic surfactants are usually raptured in contacting with crude oil, which behaves as a strong defoamer. In this article the synergistic effects between anionic surfactant SDS and negatively charged hydrophilic silica nanoparticles in stabilization of aqueous foams were examined. The results show that in either deionized (DI) water at 25 degrees C or Daqing simulated connate (SC) water with a total salinity of 6,778 mg/L at 45 degrees C, in absence of oil adding low concentration of silica nanoparticles into the SDS aqueous solutions can improve the foam performance of SDS mainly by increasing foam stability, as indicated by a synergistic effect index Se(d/s) (ratio of the composite foaming index of dispersion to that of solution) of 2.7 to 2.8. In presence of oil the foam performance of SDS in SC water at 45 degrees C can still be improved as indicated by an increased Se(d/s) of 3.7, but the maximum composite forming index is catastrophically reduced from 3222 Ls in absence of oil to 470 Ls in presence of oil. As similarly charged nanoparticles the silica nanoparticles do not adsorb at gas/liquid or oil/water interface to stabilize Pickering foams or Pickering emulsions but can improve emulsification of the oil, and the emulsified oil droplets together with the silica nanoparticles distribute in aqueous lamellae enhancing liquid viscosity and slowing down the liquid drainage in the foams. However, this effect weakens at high surfactant concentration, and addition of silica nanoparticles does not significantly reduce the interfacial tensions involved. The Enter (E), Spreading (S) and Bridging (B) coefficients of the oil in the foam systems are therefore still positive. The defoaming action of the oil in this system is not eliminated by only partially inhibited by addition of silica nanoparticles.