High temperature degradable pullulan microsphere/polymer composite for filtration loss control of water-based drilling fluids

Abstract

The effective control of water-based drilling fluid filtration rates in deep and ultra-deep wells poses a significant challenge. This study introduced a novel approach utilizing pullulan microsphere (PM) grafted with N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and dimethyl diallyl ammonium chloride as a filtrate reducer (PM-DAD). The polymer's structure was analyzed through Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis, and scanning electron microscopy. Structural characterization confirmed the successful polymerization and good thermal stability of PM-DAD. PM-DAD showed the pH response characteristics of particle size decreasing with the increase of alkalinity and the temperature response characteristics of degradation into nanoparticles after high temperature aging. The filtration loss and rheological properties of PM-DAD were assessed in accordance with the American Petroleum Institute standards. The rheological evaluation results indicated that PM-DAD could effectively maintain optimal rheological properties of the base mud after aging. PM-DAD showed remarkable filtration loss reduction ability. After aging at 200 °C, the filtration loss of the base mud was 4.7 mL, and that of the base mud containing 15 wt% NaCl was 8.2 mL. The filtration reduction mechanism of PM-DAD was investigated through mud cake analysis, particle size distribution, and X-ray diffraction. The filtration loss reduction mechanism showed that degraded nano PM-DAD intercalated between smectite clay minerals, creating electrostatic attraction and hydrogen bonds with the smectite surface, thereby facilitating the formation of a dense filter cake This research not only presents a novel approach for the utilization of pullulan but also offers a new path for controlling high-temperature filtration in water-based drilling fluids.