Study of worm-like micelles of alcohol propoxylated sulfate/alcohol ethoxylated surfactants mixtures for crude oil recovery

Systems with elongated cylindrical micelles, also known as worm-like micelles (WM) or viscoelastic surfactants (VES), have high surface activity and high viscosity, which makes them attractive in different applications such as improved oil recovery, friction reducing agents in heating and cooling fluids, household and personal care products. This study examines the carbon's chain length of alkyl propoxylated sodium sulfate anionic surfactants (C₁₆O(PO)₁₅S, C₁₄O(PO)₁₅S, and C₁₂O(PO)₁₅S) mixed with a nonionic ethoxylated surfactant on viscoelastic properties and interfacial tension. Results show that the larger the surfactant's carbon chain, the greater the possibility of forming WM. Furthermore, the propylene oxides' (PO) number and the nonionic surfactant's type of tail (linear or branched) is studied, not only on WM formation but also on WM/crude interfacial tension values. It is observed that the surfactant's molecular structure plays an important role in WM formation. By increasing the anionic surfactant's PO from 15 to 20 units, the maximum value of zero viscosity goes from 4.507 to 0.092 Pa.s and by changing the structure of the nonionic surfactant from linear (C_12-13EO₈) to branched (C_12-14EO₉) keeping the PO number of the extended surfactant constant, the zero viscosity value goes from 4.507 to 0.28 Pa.s. Likewise, the WM/crude interfacial tension reached values of the order of 10⁻³ mN/m in the salinity range studied, which makes these systems very interesting for polymer substitution in enhanced crude oil recovery (EOR).