Aqueous stability improvement of zwitterionic/anionic surfactants for ASP flooding.

摘要

In surfactant flooding, ultra-low interfacial tension (IFT) between injected fluid and crude oil is believed to be required to achieve a significantly high oil recovery and low residual oil saturation. The previous study also demonstrated that surfactant solubility in the water phase or aqueous stability is very important as well because only a nearly clear solution is able to propagate deep into the reservoir to generate the necessary interactions between surfactant molecules and crude oil. Therefore, in this study, we investigated different approaches to improving the solubility of selected surfactant formulation. These approaches include adding different cosolvents (low chain fatty alcohols), cosurfactants (surfactants in a small amount), and also alkalis. A formulation comprised of two surfactants, i.e., alkyl benzene sulfonate and cocamidopropyl hydroxysultaine which are anionic and zwitterionic surfactants, respectively was successfully developed for the designated crude oil. This surfactant mixture showed excellent IFT reduction capability. However, the solubility of this formulation is relatively poor and must be improved before field application.;As a criterion, interfacial tension is measured for different surfactant systems. In the meanwhile, surfactant stability in the aqueous phase is characterized by both visualization test and particle size distribution measurement. In general, a more clear solution with small particle size and low IFT is considered an excellent surfactant formulation.;The study conducted 8 series of tests to investigate the influence of surfactant mixing ratio, cosurfactant, different types of cosolvents and alkalis on surfactant interfacial tension and aqueous stability. The results showed that a promising surfactant formulation using selected zwitterionic/anionic surfactants should consider using alkyl ethers sulfated sodium as the cosurfactant, isopropanol or ethanol instead of n-butanol as the cosolvent, and NaOH, Na2SiO3, and Na2CO3 as the alkali candidate. Ammonia (NH4OH) that shows a poor interfacial tension property should be excluded even though very clear solutions are obtained at different NH4OH concentrations.