Stability mechanisms of viscoelastic zwitterionic-anionic surfactants enhanced foam system for low-permeability reservoirs

Abstract

Polymers are generally applied to enhance foam stability and boost the efficiency of foam flooding for enhanced oil recovery (EOR). In low-permeability reservoirs, the polymers can unavoidably damage the formation. In this study, a novel viscoelastic surfactant system was developed by combining zwitterionic surfactant erucic acid amide propyl hydroxysulfonyl betaine (EHSB) and anionic surfactant sodium dodecyl sulfate (SDS) to enhance air foam stability without damaging the formation in low-permeability reservoirs. The Waring Blender method was used to comprehensively investigate the foam parameters, including foaming volume, drainage half-life, and foam half-life under practical formation conditions. After that, an optical microscope and Turbiscan stability analyzer were used to study the stability of the foam. The interfacial viscoelasticity, electric double layer, and continuous phase viscoelasticity were investigated to clarify the stability mechanisms. The results indicate that the foam composite index of the optimum formulation 0.3 % EHSB-SDS (mass ratio = 1.1:1) system was 175500 min·mL, which is 6 times higher than that of EAB-SDS system with a same viscosity. The EHSB-SDS system also provides a certain degree of strong resistances on temperature and crude oil, which has fair stability below 55 °C and 10 % oil content. EHSB-SDS has stronger interfacial strength and foam stability than EAB-SDS system due to its higher interfacial elastic modulus and surface activity. Meanwhile, the EHSB-SDS has a higher absolute value of Zeta potential (34.91 mV) than EAB-SDS (20.66 mV), indicating a stronger electrostatic repulsion. Hence, the newly viscoelastic surfactant-enhanced foam possesses sufficient stability and exhibits great EOR potential in low-permeability reservoirs.