Polydopamine Nanospheres as a Plugging Agent in Water-Based Drilling Fluids

Inspired by the adhesion mechanism of mussels, polydopamine (PDA) nanospheres with tunable particle sizes were successfully synthesized via the oxidative self-polymerization of dopamine in an ethanol–water mixture under alkaline conditions. The plugging performance of the PDA nanospheres was systematically evaluated. The molecular structure, thermal stability, and morphology of PDA were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), solid-state NMR (ss-NMR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), zeta potential measurements, and particle size analysis. The results demonstrated that both the ethanol-to-water ratio and pH significantly influenced PDA particle size. Moreover, the particle size could be controlled within a nanoscale range. The PDA nanospheres showed excellent thermal stability, with a residual mass of 63.94% at 600 °C. High-temperature, high-pressure (HTHP) filtration, and constant-rate displacement experiments revealed that PDA nanospheres effectively reduced the permeability of filter cakes through a synergistic “flexible embedding–surface coverage” mechanism, outperforming conventional nano-SiO2. Acute biotoxicity testing confirmed that PDA nanospheres are a low-toxicity and environmentally compatible materials. This work provides both theoretical and experimental insights into the design and optimization of PDA-based nano plugging materials.