Comparative Evaluation of Anionic Surfactants (AOS, ALS, ABS, and MES) for Enhanced Oil Recovery at Varied Concentrations and Temperatures in Sandstone Reservoir

Abstract : This research aims to evaluate and compare the effectiveness of four anionic surfactants—Alpha Olefin Sulfonate (AOS), Ammonium Lauryl Sulfate (ALS), Alkyl Benzene Sulfonate (ABS), and Methyl Ester Sulfonate (MES)—for Enhanced Oil Recovery (EOR) applications in sandstone reservoirs. Experiments were conducted using five surfactant concentrations (0.5%, 0.7%, 0.9%, 1.1%, and 1.3%), a fixed brine salinity of 9000 ppm, and two temperature conditions (60°C and 80°C). Physical fluid properties including density, specific gravity, and viscosity were characterized for each surfactant solution. Results demonstrate that increasing surfactant concentration raises both density and viscosity, while increasing temperature tends to decrease these values. Phase behavior tests showed that AOS and ALS were capable of forming stable microemulsions (Winsor III) at 1.3% concentration across both temperatures, whereas ABS and MES formed microemulsions only at 60°C and higher concentrations, with a notable decline in performance at 80°C. Interfacial tension (IFT) measurements identified ALS as the most effective, reducing IFT to the optimal range for EOR (<0.01 dyne/cm), outperforming AOS, ABS, and MES. Core flooding tests further validated ALS, which delivered the highest increase in oil recovery factor (RF), achieving a 30.83% increment at 1.3% concentration and 60°C. MES followed as a promising alternative, contributing approximately a 5% RF increase under the same conditions, while AOS and ABS yielded lower enhancements. The study concludes that selection of surfactant type, concentration, and operational temperature critically influences oil recovery efficiency. ALS is identified as the most effective surfactant under the tested conditions, with MES offering additional environmental benefits and solid EOR performance at moderate temperatures. Future research is recommended to explore surfactant-polymer combinations, varied salinity scenarios, and field-scale validations to optimize EOR strategies for mature oil reservoirs.