Synthesis, Characterization, and Viscosification of Amidosulfobutaine and Zwitterionic Gemini Surfactants

The viscoelastic surfactants (VES)-based acid diverters are frequently used to divert acid flow from high-permeability layers into low-permeability for enhanced overall productivity of the treated well. In general, an optimum VES-based system possesses advantages of decrease in absorption loss, damage of reservoir, and improved adaptability of active agents to high salinity. Herein, we report the synthesis of three new zwitterionic gemini surfactants (1–3) and previously known amidosulfobutaine (C₁₈AMP3SB) has been accomplished for the investigation of diverting acid performance. The synthesis of these surfactants was achieved by the amidation of the acid chlorides of commercially available fatty acids with 3-(dimethylamino)-1-propylamine followed by subsequent reactions with appropriate sultone or ethyl 4-bromobutanoate. The synthesized surfactants were well characterized by spectroscopic methods including IR and NMR spectroscopy. The thermogravimetric analysis (TGA) results suggested that surfactants (1–3) and C₁₈AMP3SB possess excellent thermal stability, with no appreciable loss of mass up to 300°C. The viscosity measurements of the neat surfactants (1–3) and C₁₈AMP3SB were performed under various temperatures, in the presence of different concentration of calcium chloride salt with the aid shear viscosimetry. The analysis revealed that the viscosity of neat C₁₈AMP3SB increases with increase in concentration of CaCl₂. With 10% CaCl₂ solution, the viscosity was increased from 7.5 to 33.55 cPs, whereas in 20% CaCl₂ the viscosity reached to 102 cPs with rise in temperature from ambient to 90°C. Moreover, the viscosity of neat surfactants (1–3) did not exhibit any appreciable viscosity change under the experimental conditions. However, the mixture of surfactants (1–3) each in combination with C₁₈AMP3SB (1:1) displayed significant upsurge in the viscosity, up to more than 10 folds.