Assembling the Formulation Puzzle: Comparative Evaluation of Biobased and Conventional Microemulsions for Enhanced Oil Recovery

The rational design of environmentally friendly microemulsions for chemical enhanced oil recovery (EOR) remains a critical challenge, particularly in achieving interfacial efficiency and thermodynamic stability comparable to conventional petrochemical systems. In this study, we deconstruct the formulation puzzle by systematically comparing eight Winsor IV microemulsions composed of renewable and conventional components under reservoir-relevant conditions (60 °C). The systems were engineered using different combinations of nonpolar phases (toluene or pine oil), surfactants (Triton X-100 or saponified coconut oil), cosurfactants (isopropyl or ethyl alcohol), and polar phases (distilled water, saline brine, or glycerol), to reveal how molecular constituents cooperatively dictate phase architecture and physicochemical properties. Biobased formulations consistently produced significantly broader Winsor IV domains, up to 35% larger than their petrochemical analogues, while achieving low interfacial tensions (0.14–2.7 mN·m–1) and moderate viscosities (≤4.13 cP), effectively balancing injectivity with capillary desaturation potential. The synergistic pairing of saponified coconut oil with short-chain alcohols yielded flexible and resilient interfacial films, enabling enhanced performance across thermal and compositional gradients. For the first time, this work demonstrates that renewable surfactant–cosurfactant frameworks not only rival but, under the investigated thermal and salinity conditions, can surpass traditional hydrocarbon-based systems in interfacial behavior and formulation robustness, establishing a scalable and sustainable foundation for next-generation EOR applications.