Polymer nanocomposite ADA@SM as a high-temperature filtrate reducer for water-based drilling fluids and its filtration loss mechanism

High temperatures degrade drilling fluid performance and endanger drilling safety when drilling deep and ultra-deep wells. The development of a new high-temperature drilling fluid additive to maintain drilling fluid performance in high-temperature environments is critical. A polymer nanocomposite (ADA@SM) was synthesized from the monomers styrene (St), methyl methacrylate (MMA), acrylamide (AM), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and diallyldimethylammonium chloride (DMDAAC) through a free-radical copolymerization reaction. Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance ( 1 H NMR) were used to characterize the structure of ADA@SM, and transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the microstructure of ADA@SM, indicating that it had a "star-net" structure. TGA analysis showed that the thermal decomposition temperature of ADA@SM was above 274 °C. The rheological and filtration properties of drilling fluids with ADA@SM were studied before and after aging at high temperatures (150–240 °C). The rheological model of the drilling fluid containing 2.5 wt% ADA@SM was found to be consistent with the Herschel-Buckley model. After aging at 220 °C, the filtration loss for API and HTHP was 8.4 mL and 29.8 mL, respectively. Using particle size analysis and zeta potential analysis, ADA@SM produced a drilling fluid with good particle size distribution and colloidal stability in high temperature environments . SEM analysis showed that ADA@SM adsorbed on the surface of the bentonite particles, which improved the compactness of the filter cake. The relative molecular weight (Mn) of ADA@SM decreased from 59671 to 5908 after degradation at high temperatures, and ADA@SM released polymer nanospheres , which effectively reduced the filtration loss of the drilling fluid.