Abstract
The critical micelle concentration (CMC) of surfactants represent the concentration at which surfactant monomers start to form aggregates in order to minimize the energy of the electrostatic and hydrophobic interactions of the system. At this concentration, any additional surfactant molecules are not available at the interface but in aggregates in the bulk of the solution. A measure of CMC for a field surfactant gives an indication of the concentration needed for its effectiveness as an enhanced oil recovery (EOR) agent. This has been shown to be dependent on several factors including the nature of the brine, temperature, and ionic species strength. As such, for field applications, CMCs need to be measured for the particular environment that the surfactant will be used in.
In this work we have measured the CMCs for three types of EOR surfactants. The Du Noüy ring method was used with an automatic dispenser to dilute and measure surface tensions of the various surfactants at different temperatures and in different field brines. The effect of other chemical species, especially polymer was also investigated. Of the three surfactants studied, the betaine surfactant showed the lowest CMC in both injection seawater and field produced brine. It also out-performed the others in temperature stability for all types of brines. The other two surfactants were an amine oxide and an alpha olefin sulfonate. For the field brine conditions, the amine oxide proved to be the poorer performer in terms of CMC while the anionic alpha olefin sulfonate was close to the amphoteric surfactant.
Determination of CMC for real field brine conditions and at elevated temperatures provides a good insight into the performance and potential of different surfactants. Coupled with other tests like phase behavior and interfacial tension (IFT) measurements, very quick decisions can be make about the efficacy of surfactants for field application.
