Abstract:

To design an efficient targeted viscosifying binary flooding system, the mechanism for the effects of microcapsulated emulsion polymer on the interfacial tension of extended surfactants was studied. The interfacial tension of carboxylate-and sulfate-type extended surfactants （C₈P_mE_nC and C₈P_mE_nS） against n-alkanes was measured by spinning drop method. The effects of PO number, EO number and ionic headgroups on the interfacial tension of extended surfactant solutions were investigated. The experimental results showed that the helical structure of long PO chain was beneficial to the reduction of interfacial tension, while the steric effect of long EO chain was unfavorable to the reduction of interfacial tension. Only when PO number≥10 and EO number≤10, C₈P_mE_nC and C₈P_mE_nS could possibly achieve ultra-low interfacial tension. The water-soluble nonionic surfactant Tween80 could enhance the hydrophilicity of the mixed system and significantly reduce the n_min value of the extended surfactant. The oil-soluble nonionic surfactant Span80 and the extended surfactant molecules could form mixed micelles in solution, and thus did not affect the n_min value. When the interfacial activity of the extended surfactant was not strong enough, the nonionic surfactant from the “microcapsulated emulsion polymer” would compete with the extended surfactant for adsorption, and the interfacial tension increased. For those extended surfactants with strong interfacial activity, the targeted viscosifying polymer affected the interfacial tension by adjusting the hydrophilic-lipophilic balance. Both unbroken and broken microcapsulated emulsion polymer would further reduce the interfacial tension of those extended surfactants with strong oil solubility and maintain ultra-low interfacial tension. This work could have guiding significance for the design of targeted viscosifying binary flooding system.

Key words: extended surfactant, microcapsulated emulsion polymer, interfacial tension, PO number, EO number