Chemical EOR with Methyl Ester Sulfonate: Achieving Residual Oil Saturation via 2-4-Order Capillary Number Increase

This study extends the application of methyl ester sulfonate (MES), a biodegradable, anionic surfactant derived from renewable resources, for chemically enhanced oil recovery (EOR) in high-salinity (up to 700 mM NaCl) and high-temperature (80 °C) conditions. MES is demonstrated to reduce oil-water interfacial tension to low values (∼0.02 mN/m at 80 °C), alter sandstone wettability to preferentially water-wet, and form stable Winsor III microemulsions. We highlight a key advancement by systematically compiling and comparing published capillary desaturation data, showing that increasing the capillary number by a factor of 10²-10⁴ enables the system to approach irreducible water or residual oil saturation. Our experimental results align with this trend, where MES significantly increases capillary numbers through synergistic effects of interfacial tension reduction and wettability alteration. Zeta potential measurements confirm colloidal stability across a broad concentration and salinity range, while thermal analysis supports MES stability up to 90 °C. Spontaneous imbibition tests show oil recovery exceeding 28% under optimized salinity, further validating the MES efficacy. This work not only expands the operational envelope of MES for chemical EOR but also reinforces the mechanistic link between the capillary number scaling and residual oil displacement. By integrating lab-scale results with a broad data set from the literature, this study delivers a compelling foundation for deploying MES in field-scale EOR operations, particularly in mature reservoirs where sustainable and cost-effective solutions are critical.