Volume 67

Ion-Regulated Interfacial Rheology and Dynamic Recovery Mechanisms of Low-Salinity Waterflooding Yuting HE, Yuetian LIU, Rukuan CHAI, Ying MENG

Abstract

This study investigates the effect of low-salinity waterflooding on enhanced oil recovery, focusing on how different cation types (Na+, Ca2+, Mg2+) and their concentrations influence the interfacial structure and viscoelastic properties of stearic acid monolayers at the oil-water interface. The results demonstrate that low-salinity waterflooding significantly improves microscopic sweep efficiency by enhancing the stability and rigidity of the oil-water interface. This enhancement is achieved through ion-regulated modifications of the interfacial film, particularly through the formation of hydration-bridged structures. Surface pressure-area isotherms, interfacial dilational rheology, and Zeta potential measurements show that the interfacial properties are highly dependent on the type and concentration of cations. Specifically, Mg2+ produces the most significant effects, leading to the highest collapse pressure (53.7 mN·m-1), elastic modulus (19.71 mN·m-1), and a significantly reduced Zeta potential (-13.77 mV), indicating a more stable and rigid interfacial film. These effects are attributed to the stronger interactions between Mg2+ and the carboxyl groups of stearic acid, which promote tighter molecular packing and interfacial elasticity. Furthermore, the increased interfacial elasticity observed at deformation frequencies between 0.025 and 0.1 Hz supports the formation of a viscoelastic nanomembrane that resists localized deformation under flow. This enhanced interfacial structure helps suppress viscous fingering, stabilize the displacement front, and improve displacement efficiency. As a result, low-salinity waterflooding, particularly with optimized cation concentrations, significantly enhances oil recovery by improving microscopic sweep efficiency in heterogeneous reservoirs. The study provides valuable insights into the mechanisms behind low-salinity waterflooding and highlights the critical role of ionic regulation in optimizing oil recovery processes.

Keywords Surface pressure, Interfacial dilational rheology, Stability, Zeta potential, EOR