Abstract:

To meet the requirements of oil production in high-salinity reservoirs, tetradecanoic acid monoethanolamide ether sulfonate （C14NE3S） was prepared from tetradecanoic acid monoethanolamide by ethoxylation and sulfonation. The solubility and the surface tension of the product were measured. The properties of C14NE3S when mixed with tetradecanoic acid diethanolamide （C14DN） were investigated. The interfacial activity between the binary mixed system and Changqing crude oil in mineralized water was also measured. The results showed that the aqueous solution of C14NE3S remained clear in 30% NaCl at above 30 ℃. The critical micelle concentrations of tetradecanoic acid monoethanolamide polyoxyethylene ether （C14NE3） and C14NE3S in distilled water were 0.07 and 0.158 mmol/L, respectively, indicative of the enhancement of hydrophilicity of C14NE3S due to the multiple hydrophilic groups. The theoretical study on solution thermodynamics showed that C14NE3S had synergism with C14DN for the formation of mixed micelles, especially when the molar fractions of C14NE3S were fixed to 0.2 and 0.4, the mixed systems showed moderate interaction. The interfacial tension of mixed surfactants in which the molar fraction of C14NE3S was 0.2 could be ultra-low to low （i.e., 10^-3-10^-2 mN/m） in the presence of 0.3%-10% NaCl. The interfacial tension of mixed surfactant systems when n（C14NE3S） ∶n（C14DN） = 2∶3 and 3∶2 could be ultra-low （order of magnitude, 10^-3 mN/m） at 0.3%-3% NaCl and 5%-10% NaCl, respectively. The mixed system withn（C14NE3S） ∶n（C14DN） of 1∶4 could show ultra-low interfacial tension at 0.3%-1% NaCl. This work could have a certain guiding role for the development of temperature- and salt-resistant oil-displacement surfactant systems.

Key words: tetradecanoic acid monoethanolamide ether sulfonate, alkanolamide, interaction, surface/interfacial tension, salt resistance