A CFD–DEM Study on Non-Spherical Cutting Transport in Extended-Reach Wells Under Rotary Drilling

To investigate the accumulation and transport behavior of non-spherical particles during rotary drilling in extended-reach horizontal wells, a CFD–DEM numerical simulation study was carried out based on actual field drilling parameters. The effects of flow rate, drillpipe rotation speed, drilling fluid viscosity, and particle shape on cutting transport were systematically analyzed in terms of spatial distribution of particle concentration, microscopic movement velocity of particles, and annular pressure drop. A dimensionless pressure-drop–flow-pattern chart was then constructed to characterize the coupled flow–particle transport behavior. The results indicate that flow rate, rotation speed, viscosity, and cutting shape all markedly affect the transition from a stationary cutting bed to suspended transport. Increasing the flow rate, rotation speed, and viscosity promotes hole cleaning. However, once these parameters exceed a certain threshold, further improvements in cutting removal are accompanied by a sharp increase in annular pressure drop. The final Π–DPD dimensionless chart was developed, which can be used for rotary drilling parameter optimization in extended-reach wells, and Π ≈ (2.5–3.1) × 104 is recommended as the preferred range.