Investigation on the plugging performance of polybutyl methacrylate as nano plugging agent used in the water-based drilling fluids

Abstract This study presents polybutyl methacrylate (PBMA), a novel organic nanoscale plugging agent synthesized through emulsion polymerization, to mitigate shale wellbore instability in water-based drilling fluids. The PBMA particles feature a spherical-to-platelet morphology with an average diameter of 79.9 nm (range: 37.7–126.8 nm), enabling effective sealing of nanoscale pores (< 100 nm) within shale matrices. Comprehensive characterization, including FTIR spectroscopy, TGA, and SEM analysis—confirms their structural integrity, functional group composition (ester, methyl, and long-chain hydrocarbons), and thermal stability (decomposition temperature up to 197.7 °C), surpassing most organic nanomaterials such as carbon nanotubes. Rheological assessments demonstrate negligible interference with drilling fluid properties: even at a 2.0 wt% PBMA concentration, variations in apparent viscosity (AV), plastic viscosity (PV), and yield point (YP) remain below 5%, significantly reducing dependence on conventional thickeners. Permeability tests of filter cakes reveal that 1.5 wt% PBMA achieves a 75.2% plugging efficiency, reducing permeability to 3.79 × 10⁻⁶ μm2—a value comparable to the intrinsic permeability of shale, which suggests a dual mechanism combining physical pore blockage and chemical adsorption. Compared to inorganic nanomaterials (e.g., SiO₂, Al₂O₃), PBMA exhibits advantages in simplified synthesis, production costs reduced by an order of magnitude, and environmental compatibility. Relative to organic alternatives (e.g., polystyrene, carbon nanotubes), PBMA distinguishes itself through superior thermal stability and intrinsic functionalization potential without requiring surface modifications. This study establishes PBMA as a viable solution for high-temperature deep wells (> 197.7 °C) and low-permeability shale reservoirs, providing a cost-effective and scalable strategy to address shale hydration-induced wellbore collapse and fluid loss. Future applications could expand to hybrid systems (e.g., integration with slow-release acids for synergistic dissolution-plugging effects) or smart-responsive materials (e.g., pH/temperature-triggered dynamic sealing) to enhance performance in extreme downhole environments.