Evaluation of zwitterionic and polymeric surfactant adsorption for enhanced oil recovery in sandstone reservoirs with high salinity conditions
Elias Ghaleh Golab
Abstract
Zwitterionic surfactants and their polymeric derivatives have attracted significant attention due to their superior thermal and ionic stability under harsh reservoir conditions, making them promising agents for enhanced oil recovery (EOR). In this study, a novel zwitterionic polymeric surfactant with a specifically designed amphiphilic structure was synthesized using a modified polymerization technique. Both the zwitterionic surfactant and its polymeric analog, which includes a newly designed hydrophobic moiety, were fully characterized. Their adsorption behavior was tested on sandstone samples typical of oil reservoirs, which are mainly composed of silicon, aluminum, magnesium, and iron, reflecting a complex surface chemistry. Adsorption experiments were conducted at concentrations ranging from 1,000 to 15,000 mg/L in deionized water, synthetic brines containing NaCl, MgCl₂, and CaCl₂ (10,000–30,000 mg/L), and actual reservoir brine. Results showed that adsorption increased with salinity. The presence of divalent cations (Ca 2 ⁺, Mg 2 ⁺) enhanced ionic bridging, compressed the electrical double layer, and strengthened hydrophobic interactions, which improved adsorption stability. The polymeric surfactant consistently showed higher adsorption capacity and greater stability compared to its monomeric counterpart. Adsorption data fit well to classical isotherm models—Langmuir, Freundlich, Temkin, Hill, and Dubinin–Radushkevich—with the Langmuir model providing the best description of monolayer adsorption at low concentrations. Interfacial tension (IFT) measurements demonstrated a sharp reduction near the critical micelle concentration (CMC) for the zwitterionic surfactant, indicating effective adsorption at the oil–water interface. In contrast, the polymeric surfactant exhibited a more gradual decrease in IFT, attributed to its molecular rigidity. Conductivity tests supported these observations, showing higher ionic mobility for the zwitterionic surfactant, while steric hindrance from the polymer backbone restricted ion movement. This study offers new insights into the adsorption mechanisms and interfacial behaviors of zwitterionic surfactants and their polymeric derivatives under high-salinity, multivalent ion conditions, demonstrating the superior adsorption capacity and stability of the synthesized polymeric surfactant. These findings highlight the potential of this novel polymeric surfactant for improved EOR performance in sandstone reservoirs under harsh reservoir environments.