Abstract:

A new anionic-nonionic surfactant with branched hydrophobic group was prepared using C₁₆ Guerbet alcohol by co-polymerization of propylene oxide （PO） and ethylene oxide （EO） followed by sulfation with aminosulfonic acid. This surfactant （C₁₆GA-PES） shows excellent aqueous solubility, good tolerance to inorganic electrolytes such as sodium chloride （NaCl） and calcium chloride （CaCl₂）, and good surface activity （cmc=1.15×10^-6 mol/L）. When dissolved in Daqing formation water （pH=8-9） with a total salinity of 6 788 mg/L, including 23 mg/L Ca²⁺ and 31 mg/L Mg²⁺ at 45 ℃, the C₁₆GA-PES solely can reduce the interfacial tension （IFT） between Daqing light crude oil and formation water to ultralow （<0.01 mN/m）; for the slightly heavy crude oil from the third type of reservoir in Daqing oilfield, ultralow IFT can be achieved by mixing the C₁₆GA-PES with a small fraction of more hydrophobic surfactant, 1,3-didecyl glyceryl ether hydroxypropyl sulfobetaine （diC₁₀GE-HSB）. The new surfactant adsorbs at the oil/water interface constituting a monolayer which has high alkyl chain density and a transition structure from strongly hydrophobic to weak hydrophobic-weak hydrophilic and to strong hydrophilic, resulting in strong interactions between the monolayer and oil molecules and making ultralow IFT easily achievable. It is also noticed that, the nonionic intermediate produced by co-polymerization of PO and EO has low viscosity, which is beneficial to pipeline transport and sulfation with SO₃/air mixture.

Key words: oil-displacing agent, alcohol ether sulfate, copolymerization, branched alkyl, ultralow IFT