A zwitterionic copolymer as fluid loss reducer for water-based drilling fluids in high temperature and high salinity conditions

With the exploration and development of deep and ultra-deep oil/gas resources, higher challenges have been placed on the performance of water-based drilling fluids (WBDFs). Integrating synergistic characteristics such as excellent high temperature- and salt-resistance, rheology, and fluid loss control capabilities is still a massive challenge for water-based drilling fluid loss reducers. Herein, an innovative temperature- and salt-resistant zwitterionic copolymer filtration reducer was synthesized using N, N-dimethyl acrylamide, 1-(2-carboxyethyl)3-vinyl imidazolium chloride, sulfobetaine vinyl imidazole through free radical copolymerization. Due to the excellent rigid cationic imidazole ring and salt-resistant hydration groups in the copolymer, the copolymer can be efficiently adsorbed on the surface of bentonite particles through strong electrostatic force and hydrogen bonds, thus maintaining the excellent hydration and dispersibility of bentonite particles. Even after aging at high temperatures (up to 200 ???C) and high salinity (saturated salt) conditions, the DCS-based drilling fluids still exhibit excellent rheological and filtration properties (FLAPI < 10 mL), showing the potential for application in deep and ultra-deep drilling operations.