Effect evaluation of binary self-adapted system without alkali after polymer flooding

After polymer flooding, the oil reservoir exhibits severe heterogeneity, and the remaining oil is generally highly dispersed, and the salt or alkali of ASP (alkali-surfactant-polymer) system have negative impacts. To address these problems, an alkali-free binary self-adapted system has been developed. Through experimental methods such as instrument detection and physical simulation, the nonionic surfactant suitable for high viscosity with PPG (pre-particle gel) particles was selected. The alkali-free binary self-adapted system was systematically evaluated, and a three-pipe parallel oil displacement experiment was conducted to verify the effect. The research results show that: when the concentration of A606 surfactant is between 0.05% and 0.4%, the alkali-free binary self-adapted system can achieve ultra-low interfacial tension of 10⁻³ mN/m level. Compared with the weak-alkali ASP self-adapted system, the alkali-free binary self-adapted system has better stability and emulsifying performance. After 90 days, the viscosity retention rate is 80.9% and ultra-low interfacial tension is maintained. The anti-adsorption performance is basically the same, and after 5 cycles of adsorption on oil sand, ultra-low interfacial tension is still maintained. After 6 adsorptions, the viscosity retention rate is 71%. Physical simulation experiments have shown that the alkali-free binary self-adapted system has better control and flooding effects than high concentration polymer flooding. Under optimal formulation conditions, the alkali-free binary self-adapted system applied after polymer flooding can increase oil recovery by 15.5% in the three tube parallel model.