CFD–DEM Investigation of Material Composition Effects on the Transportability of While-Drilling Lost Circulation Materials in Directional Tools

The passability (transport behavior) of while-drilling lost circulation materials (LCMs) through directional tools is strongly influenced by material composition and particle characteristics. In this study, a coupled computational fluid dynamics–discrete element method (CFD–DEM) model is developed to systematically evaluate the effects of particle size distribution, concentration, morphology, and fiber inclusion on LCM transport behavior. Visualization experiments conducted using a transparent screen section demonstrate good agreement with the simulated pressure-drop evolution, supporting the validity of the model. The results reveal that increasing particle size from 1.2–1.6 mm to above 2.8 mm shifts the system from a stable transport regime to one with a high risk of plugging, even at relatively low concentrations. Plugging risk rises markedly when particle concentration exceeds 30–35%. Multimodal particle size distributions enhance transport performance, achieving efficiencies of approximately 0.07%, compared with less than 0.035% for monomodal systems. Irregular particle shapes increase force-chain normal forces from 0.009–0.010 N to 0.017–0.020 N, while fiber inclusion significantly reduces steady-state flow velocity from about 1.6–1.7 m/s to below 0.6 m/s, thereby diminishing passability.