Synergistic Effect of Biosurfactant and Chemical Surfactant with Salinity on Enhanced Oil Recovery

Surfactant-induced enhanced oil recovery mobilizes trapped oil in the tertiary stage, but single surfactants are often costly and less effective. This study investigates the synergistic effect of rhamnolipid biosurfactant combined with chemical surfactants (cationic; cetyltrimethylammonium bromide (CTAB), anionic; sodium dodecyl sulfate (SDS), nonionic; Triton X-100 (TX-100) and zwitterionic; and N,N-dodecyl dimethylamine N-oxide (DDAO)) and sodium chloride for enhanced oil recovery (EOR). The optimized formulation of rhamnolipid (60 ppm) with 5% NaCl, exhibiting an interfacial tension (IFT) of 1.81 ± 0.45 mN/m was systematically evaluated for various mixed systems. The IFT values for CTAB, SDS, TX-100, and DDAO at their critical micelle concentrations (CMCs) were found to be 0.136 ± 0.003, 0.95 ± 0.0102, 2.301 ± 0.166, and 0.068 ± 0.001 mN/m, respectively. The maximum reduction was observed in the case of DDAO, followed by CTAB. Furthermore, the addition of CTAB and DDAO with RL60 + 5% NaCl mixture resulted in a significant reduction in IFT values, achieving a plateau of 7.25 × 10–3 and 6.47 × 10–3 mN/m at 1 CMC (362.45 ppm) of DDAO and 1 CMC (335 ppm) of CTAB, respectively. This hybrid system improves oil recovery efficiency by decreasing IFT, modifying rock wettability, and enhancing the mobility ratio. The core flooding experiments illustrated the augmented recovery ability of this formulation. The RL60 + 5% NaCl system alone attained an extra oil recovery of 17.86%, whereas the coupling with CTAB and DDAO (at CMC) enhanced the recovery values to 33.08 ± 1.95 and 30.68 ± 1.32%, respectively. This significant enhancement underscores the synergistic interaction between CTAB/DDAO and the rhamnolipid-salt in decreasing IFT and altering wettability toward a more water-wet state, thereby promoting the mobilization of entrapped oil. The results affirm that the combination of biosurfactants with chemical surfactants and salts markedly improves oil recovery efficiency in MEOR applications.