A novel nano-lignin-based amphoteric copolymer as fluid-loss reducer in water-based drilling fluids

In the study, nano-lignin (Nano-LS) was gradually formed from inside to outside via layer-by-layer self-assembly owing to the interaction of π-π bonds, and a novel amphoteric polymer, Nano-LS-g-DAD, was synthesized by grafting N, N-dimethylacrylamide (DMAM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyl dimethyl ammonium chloride (DMDAAC) onto the Nano-LS in an aqueous solution using ammonium persulfate and sodium bisulfite as initiators. The structure of the resulting graft copolymer was characterized via Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H-NMR) methods. Thermogravimetric analysis (TGA) revealed the thermal stability of Nano-LS-g-DAD, and the thermal decomposition of Nano-LS-g-DAD was observed above 281 ℃. Nano-LS-g-DAD were prepared also for water-based drilling fluids (WBDFs), and rheological and filtration properties were evaluated before and after aging at 260 ℃ for 16 h. The results revealed that the fluid loss (FLAPI) of WBDFs with Nano-LS-g-DAD was only 8.0 mL after aging at 260 ℃ for 16 h in a filtration test conducted as per American Petroleum Institute (API) standards. It indicated that the Nano-LS-g-DAD still maintained positive filtration reduction performance in WBDFs at ultra-high temperature. The fluid-loss control mechanism of Nano-LS-g-DAD for WBDFs was investigated via Zeta potential analysis and clay particle size distribution measurement. Simultaneously, WBDFs with Nano-LS-g-DAD also maintained positive rheological and filtration properties under the invasion of salt and calcium ions. Furthermore, the acute toxicity value (EC50) of Nano-LS-g-DAD was 54,800 mg/L, which indicated that it was environmentally friendly.