Ternary Copolymer as a High‐Temperature Viscosity Reducer for Water‐Based Drilling Fluids

ABSTRACT Drilling fluid plays many important roles in drilling operations of oil and gas wells, and the research on the rheological properties of drilling fluid to combat several challenges has gained attention in recent years. The environmentally friendly ternary copolymer drilling fluid viscosity reducer poly‐ISAD was designed and synthesized from itaconic acid (IA), sodium p‐styrene sulfonate (SSS), 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS), and dimethyl diallyl ammonium chloride (DMDAAC), and the key technical parameters were obtained based on the single factor experimental method. Then, the chemical structure, molecular weight, thermal stability, and microscopic morphology of poly‐ISAD were characterized by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (H 1 ‐NMR), gel chromatography (GPC), thermogravimetric analysis (TG‐DTG), and scanning electron microscope (SEM). Moreover, the poly‐ISAD was introduced into polymer‐based drilling fluid to study its rheological, filtration, and inhibition performances. As a result, the chemical structure of poly‐ISAD is consistent with the design, with excellent thermal stability, and the starting temperature for thermal decomposition of polymer molecular chains is 223°C. The weight average molecular weight ( M w ) and number average molecular weight ( M n ) of poly‐ISAD are 1.3396 × 10 6 g/mol and 7.1652 × 10 5 g/mol, respectively, and the 0.5 wt% poly‐ISAD solution shows a uniform network structure after freeze‐drying. Simultaneously, the poly‐ISAD had an excellent reducing effect on the viscosity of polymer‐based drilling fluids; specifically, the apparent viscosity (AV) and yield point (YP) of polymer‐based drilling fluids with 0.5 wt% poly‐ISAD were reduced by 40.5% and 70.5%. Meanwhile, the results show that the poly‐ISAD has excellent filtration and inhibition performances, and the API filtration volume (FL API ) of polymer‐based drilling fluids was reduced from 15.4 to 9.0 mL and 6.9 mL by 1.0 and 1.5 wt% poly‐ISAD, respectively. Besides, the mechanism of poly‐ISAD on the reducing viscosity effect of polymer‐based drilling fluids was studied via particle size analysis, zeta potential and SEM. The innovation of this study is that a novel viscosity reducer poly‐ISAD is designed and synthesized for use in high‐temperature oil and gas reservoirs; the performance and mechanism are investigated, which provided a theoretical reference for other research.