Insight into hydrophobic interactions between methyl ester sulfonate (MES) and polyacrylamide in alkaline-surfactant-polymer (ASP) flooding

The interaction between methyl ester sulfonate (MES) surfactant and polyacrylamide (PAM) polymer in alkaline-surfactant-polymer (ASP) flooding due to electrostatic charges and hydrophobicity of both elements at the interface was investigated. In the ASP flooding, sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) were used as alkali. At high PAM concentrations, the strong hydrophobic interaction between the PAM backbone and the carbon chain of MES destabilizes surfactant packing at the interface, increasing interfacial tension (IFT). The higher conductivity value of the ASP slug (15 mS/cm) compared to the alkali-surfactant (AS) slug (7 mS/cm) indicates a strong electrostatic interaction caused by the rapid mobilization of free surfactant molecules across the PAM backbone at the water-oil interface. The lowest IFT value for ASP flooding was 0.28 mN/m. Sand pack flooding tests showed that the optimum PAM concentration in ASP flooding was 1,000 ppm, resulting in a 20-35% oil recovery. A negative effect of PAM on the oil recovery was observed at a higher PAM concentration of 9,000 ppm. IFT and mobility ratios were irregularly related to the oil recovery. At 1,000 ppm PAM, the oil recovery for ASP slug with MES and commercial surfactant sodium dodecyl sulfate (SDS) was 25% and 20%, respectively, indicating that MES is superior to SDS.

Automated summary

The study investigated the interaction between methyl ester sulfonate (MES) surfactant and polyacrylamide (PAM) polymer in alkaline-surfactant-polymer (ASP) flooding, finding a strong hydrophobic interaction affecting interfacial tension and the impact of PAM concentration on oil recovery in the process.