CFD-DEM-Based Study on Particle-Size Matching of Bridging Particles in Multi-Scale Fractures

To address the limitation of traditional particle-size matching rules in lost circulation control for multi-scale fractured formations, coupled CFD-DEM simulations and laboratory simulated fracture-plugging evaluation experiments were performed on multi-scale wedge-shaped fractures. A dimensionless stability coefficient S was defined from the pressure-drop response. Gaussian process regression (GPR) was then used to establish the response relationship of S with fracture aperture and bridging particle-size ratio, forming a particle-size matching chart for multi-scale fractures. The results show that particle plugging-layer morphology and pressure-bearing response vary with fracture size. Suitable particle-size ratios allow bridging particles to form stable packing zones inside fractures and exhibit high pressure-bearing capacity, whereas smaller or larger ratios lead to deep migration, erosion-induced instability, or false plugging at the fracture inlet. The preferred particle-size ratio is 0.25-0.40 for 0.2-1 mm fractures and 0.35-0.45 for 1.5-2.5 mm fractures. The chart agrees with experimental data, with R²=0.8674, indicating good fitting accuracy within the research range.