New Series of Double-Chain Single-Head Nonionic Surfactants: 1,3-Dialkyl Glyceryl Ether Ethoxylates for Surfactant-Polymer Flooding

A new series of nonionic surfactants with double hydrocarbon tails and a single polyoxyethylene (POE) chain 1,3-dialkyl glyceryl ether ethoxylates with an alkyl length between diC(8) and diC(12) and ethylene oxide (EO) number between 3.9 and 25.6 were synthesized and characterized. The correlation of their surfactant-polymer (SP) flooding behavior with the alkyl length and EO number were studied. Although the individual Surfactants can be made highly surface-active by matching the alkyl lengths with an appropriate EO number as reflected by the low critical concentration range of 6 x 10(-7) to 9 x 10(-5) Mol/L and gamma(cmc) as low as 26.5-30.5 mN/m at 25 degrees C, they are not good surfactants for SP flooding when used alone since ultralow interfacial tension (IFT) between Daqing crude oil and connate water can only be achieved by a few members with short POE chains or hydrophile-lipophile balance (HLB) numbers near 7-8, which are poorly soluble in water. However, those with long POE chains exhibit excellent synergism in reducing Daqing crude oil/connate water IFT by mixing with a highly hydrophobic surfactant, didodecylmethylhydroxylpropyl sulfobetaine (diC(12)HSB). Ultralow IFT between 10(-3) and 10(-4) mN/m can be achieved in a wide range of total surfactant concentrations (0.3-10 mM) at 45 degrees C The binary mixed systems also possess good resistance against adsorption by Daqing sandstone and the ability to maintain negatively charged surfaces water-wet over a Wide concentration range, as well as a tendency to form crude oil-in-water (O/W) emulsions, which are all beneficial for high oil recovery in SP flooding: This synergism between nonionic surfactants and the sulfobetaine surfactant may be responsible for the excellent behavior of binary mixtures and the double alkyl chains in nonionic surfactatitS, which enhance the interaction between the surfactant monolayer and crude oil, making them superior to the conventional nonionic surfactants with a monoalkyl tail. Although the nonionic-surfactants with long POE chains and varying alkyl lengths (diC(8)-diC(12)) behave similarly, those with diC(8) alkyls are generally superior due to their excellent properties and relatively low molar mass (less dosage).