Effect of internal olefin on the properties of betaine-type zwitterionic surfactants for enhanced oil recovery

In this report, four in-house synthesized betaine-type zwitterionic surfactants containing unsaturated and saturated hydrophobic tail as well as carboxylate and hydroxy-sulfonate head groups were investigated. The two surfactants containing unsaturated tail showed excellent solubility in deionized water, sea water (57,643 ppm) and formation water (213,734 ppm). However, the other two surfactants containing saturated tail exhibited poor solubility regardless of the nature of the head group, and hence they were not evaluated further. The thermogravimetric analysis results of the surfactants containing unsaturated tail revealed excellent short-range heat stability and the major weight loss was observed above 200 °C. The surfactants containing unsaturated tail exhibited excellent long-range heat stability and the FTIR and NMR spectral characterization of the aged sample of surfactants in seawater for 15 days at 90 °C showed no change in chemical structure. The critical micelle concentration (cmc) of the surfactants decreased by increasing the salinity of the water. However, hydroxy sulfobetaine showed lower cmc value (1.78 × 10⁻⁵ mol/L) compared to the carboxybetaine (1.88 × 10⁻⁵ mol/L). Moreover, surface tension corresponding to cmc (γ_cmc) increased by increasing the salinity of the water. Rheological studies of the polymer-surfactant hybrid demonstrated that the increase in the surfactant concertation in deionized water lowers the viscosity and storage modulus of the polymer; however, in sea water, the surfactant addition showed negligible effect. The betaine-type zwitterionic surfactants exhibited excellent salt tolerance, surface, and thermal properties and may be a material of choice for enhanced oil recovery in harsh condition reservoir.