A novel critical velocity model for the incipient motion of non-spherical particles on cuttings bed in extended reach wells

Accurately predicting the minimum velocity required to initiate particles movement on a cuttings bed surface during drilling operations is crucial for efficient and cost-effective removal of deposited particles. However, current models neglect the influence of particle shape on the drag coefficient and static friction coefficient during rolling and sliding on a cuttings bed. Accordingly, this study developed an experimental setup for cuttings transport and employed both theoretical analysis and experimental methods to investigate the critical velocity for the incipient motion of particles under various operational conditions. A novel semi-mechanical criterion model was developed for the incipient motion of particles, incorporating a shape correction factor for non-spherical particles. A balance equation for the threshold Shields number, determined by particle driving forces and resistances, was established, and a numerical procedure was formulated to determine the critical velocity for the incipient motion of particles. The model predictions show strong agreement with experimental results. The study found that higher eccentricity, inclination, and fluid viscosity increased the difficulty of initiating particle movement on the cuttings bed surface, thus requiring higher annular velocities for effective cuttings removal. Conversely, increasing particle size facilitated easier removal of the cuttings bed. Compared to non-Newtonian fluids, Newtonian fluids proved more effective in cuttings removal. The findings of this study are significant for optimizing hole cleaning parameters and improving the efficiency of cuttings removal.