Nanoparticle transport and plugging in non-Newtonian drilling-fluid flow through three-dimensional porous media

Transport and retention of nanoparticles in non-Newtonian drilling fluids through porous media are critical for evaluating the sealing potential of micrometer-scale leakage channels in low-permeability reservoirs. A three-dimensional pore-scale model (43 × 25 × 8 μm3) was developed to investigate nanoparticle transport and flow restriction in a shear-thinning drilling fluid. The fluid rheology was described by the Meter model, and nanoparticles were tracked using a two-way-coupled dense discrete phase model. A user-defined concentration–viscosity relation allowed the local particle volume fraction to dynamically modify the effective viscosity. Nanoparticles preferentially accumulated near the inlet, on upstream-facing matrix surfaces, and in constricted throats, forming bridge-like particle-rich regions across the thickness direction. Approximately 80% and 91% of the final retained-particle number were reached by 30 and 40 s, respectively. At 80 s, the lower-Péclet-number case (Pe = 9.4 × 103) retained ∼1.52 × 104 particles, over four times the ∼3.6 × 103 retained at Pe = 4.8 × 104. Because the particle injection rate was fixed while the inlet velocity varied, this difference arose from the combined effects of convection, residence time, and inlet particle concentration. Increasing the matrix-sphere diameter from 2.5 to 3.5 μm reduced the final retained-particle number from ∼1.82 × 104 to 1.53 × 104, while increasing the domain-volume-averaged static pressure from ∼41 to 163 Pa. The heterogeneous structure retained more particles during rapid filling but fewer during intermediate bridge-like accumulation.