A Rigid‐Ring Structured Polyampholyte Copolymer as a Fluid Loss Agent for High‐Temperature and High‐Salinity Water‐Based Drilling Fluids

With the development of oil and gas resources to deep and ultra‐deep formations, the drilling process often faces complex conditions of high temperature and high salinity. It is still a challenge to prepare fluid loss reducers with excellent rheological properties and fluid loss control properties. In this study, a polyampholyte copolymer PDADS was synthesized from N, N‐dimethylacrylamide (DMAA), 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS), dimethyldiallylammonium chloride (DMDAAC), and sodium (4‐vinylphenyl) methanesulfonate (SVM). FT‐IR, 1 H NMR, XPS, GPC, and TGA characterization confirmed its successful synthesis and excellent thermal stability. When 3.0 wt% PDADS was added, the FL API of the drilling fluid was 5.2 mL and the FL HTHP was controlled at 26.0 mL at 230°C and 15 wt% NaCl. Under high temperature and high salinity conditions, PDADS was adsorbed on the surface of bentonite particles through hydrogen bonding and electrostatic interaction, which promoted its uniform dispersion and helped to form a dense mud cake to significantly reduce the fluid loss. In summary, PDADS is expected to play an important role in drilling operations in ultra‐high temperature and high salinity formations.