Preparation and performance evaluation of sulfate-quaternary ammonium Gemini surfactant

• Three sulfate-quaternary ammonium Gemini surfactants with different carbon chain lengths were synthesized. • The surface and interface properties, and salt and temperature resistance were evaluated in detail. • The carbon chain length has a certain effect on the properties of amphoteric Gemini surfactants. • EOR of the C 12 ZGS surfactant was 11.63% in low permeability reservoirs and more than other two surfactants. Sulfate-quaternary ammonium amphoteric Gemini surfactants with hydrophobic chains (C 12 ZGS, C 14 ZGS and C 16 ZGS) were prepared using formic acid, formaldehyde, long-chain tertiary amine, epichlorohydrin, chlorosulfone and NaOH. Their structures were characterized by IR and 1 H NMR, and the synthesized target products was confirmed. The critical micelle concentrations (CMCs) of C 12 ZGS, C 14 ZGS and C 16 ZGS were 5.4 × 10 −4 mol/L, 3.1 × 10 −4 mol/L and 2.8 × 10 −4 mol/L, respectively. Their corresponding surface tensions were 28.62 mN/m, 30.98 mN/m and 32.45 mN/m. It was found that the surface tension increases with increasing hydrophobic chain length. The three Gemini surfactants have good emulsifying and foaming properties for kerosene, and they have good solubility at low temperature. The results of thermogravimetric analysis (TGA) showed that the decomposition temperatures of C 12 ZGS, C 14 ZGS and C 16 ZGS were 153 °C, 157 °C and 150 °C, respectively. The salinity resistance of C 12 ZGS reached 4 × 10 4 mg/L, C 14 ZGS reached 5 × 10 4 mg/L, and the salinity resistance of C 16 ZGS was worst. C 12 ZGS and C 14 ZGS can reduce the oil–water interfacial tension to 10 −2 orders of magnitude, but C 16 ZGS can only reduce it by 10 −1 orders of magnitude. The stability of the surfactant flooding system was evaluated by aging time. Under the simulated reservoir formation environment, three amphoteric Gemini surfactants with different chain length (C 12 ZGS, C 14 ZGS, C 16 ZGS) can enhance oil recovery by 11.63%, 10.91% and 9.87% respectively.