Synthesis of a zwitterionic quaternary ammonium polymer and its application in fluid loss control for water-based drilling fluid

With the continuous progress of exploration and development of deep and ultra-deep oil and gas reservoirs in China, high temperature and high salinity environments pose substantial challenges to the effectiveness of drilling fluids. A high-temperature and salt-resistant zwitterionic polymer fluid loss additive (HTS-COFL) was synthesized. By introducing specific functional groups into the molecular chain, the stability and fluid loss reduction performance of this additive in high temperature and high salinity environments have been enhanced. HTS-COFL is prepared from acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), dimethyldiallylammonium chloride (DMDAAC), and N-acryloylmorpholine (ACMO) as monomers through free radical polymerization in aqueous solution. The molecular structure and thermal resistance of the polymer were evaluated using Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR) techniques. Additionally, its rheological and fluid loss properties were tested under different temperatures, salt concentrations, and calcium ion environments. The results indicate that the drilling fluid with HTS-COFL added exhibits excellent high temperature and high salinity resistance. The outstanding performance of HTS-COFL is mainly attributed to the synergistic effect of functional groups such as sulfonic acid, quaternary ammonium salt, and morpholine ring. These groups not only enhance the rigidity and steric hindrance of the polymer chain but also improve its adsorption capacity for bentonite particles. This study offers scientific guidance for the development of fluid loss additives suitable for high-temperature and high-salinity reservoirs by exploring the introduction of functional groups and their synergistic effects. This is conducive to enhancing the efficiency and economic feasibility of water-based drilling fluids under complex downhole conditions and holds significant theoretical and practical value.