pH-Responsive Supramolecular Self-Assembly of an Aromatic Zwitterionic Surfactant-Polyamine System for High-Temperature Clean Fracturing Fluids

Abstract

To address the thermal limitations inherent to conventional viscoelastic surfactant (VES) fracturing fluids, a novel aromatic zwitterionic surfactant, erucamidopropyl dimethyl carboxybenzyl ammonium chloride (ECBA), was synthesized and formulated with diethylenetriamine (DETA) to construct a supramolecular clean fracturing fluid (CFF) system. Comprehensive rheological evaluations revealed that the ECBA/DETA system achieved optimal performance at a total concentration of 4.0 wt % and pH 3.95. Mechanistically, the pH-responsive protonation of the carboxyl and amino moieties synergistically reinforced intermolecular electrostatic interactions and hydrogen bonding, driving the self-assembly of a robust supramolecular network. Cryo-SEM observation, combined with DLS measurements and packing parameter analysis, revealed a distinct porous network morphology and provided complementary evidence for the pH-dependent self-assembly and viscoelasticity of the system. Consequently, the optimized fluid exhibited elastic-dominated viscoelastic behavior with outstanding thermal and shear stability up to 110 °C. At 90 °C, the proppant settling velocity was remarkably suppressed to 0.750 cm/min, indicating superior proppant-carrying capacity. Furthermore, the incorporation of a DTPA chelating agent significantly enhanced the system’s resistance to Ca2+ ions. Regarding reservoir protection, complete gel breaking was achieved within 1 h using 10% kerosene at 90 °C, yielding an ultralow residue content of 0.147 mg/L. The resulting gel breaking fluid displayed reduced surface and interfacial tensions (22.7 and 0.051 mN/m, respectively), a high clay antiswelling efficiency of 85%, and favorable emulsification/demulsification behavior. Collectively, these results demonstrate that the synergistic noncovalent interactions between the aromatic zwitterionic surfactant and DETA under acidic conditions effectively stabilize the supramolecular network, providing a promising molecular design strategy for high-temperature and formation-friendly CFFs.