Application of zwitterionic copolymer as a filtration control agent against high temperature and high salinity for water-based drilling fluids

Minimizing the filtration loss of water-based drilling fluids (WDFs) is critical for ensuring the safe development of oil. In this study, a zwitterionic copolymer (ZCP) was prepared to provide effective filtration control of WDFs. The expected product was verified using Fourier Transform Infrared (FT-IR). A thorough assessment was carried out to evaluate the rheological properties and filtration performance of WDF containing varying concentrations of ZCP. The mechanism of ZCP was proposed based on the analysis of the absorption, zeta potential, particle size distribution, and microstructure of filter cakes for bentonite. The results showed that ZCP could maintain thermally stable at 290 & DEG;C. Even after thermal aging at 200 & DEG;C, the filtration volume of the WDFs with 2% ZCP was only 9.6 ml despite the presence of saturated salt. This remarkable performance could be attributed to the strong adsorption of bentonite by multiple ZCP molecules through hydrogen bonding and electrostatic forces. The absorption of ZCP enhanced the dispersion of bentonite in WDFs, which facilitated the formation of an excellent filter cake to effectively suppress filtration loss. The research was instructive for polymeric filtration control agents with high temperature and salt resistance.