A CFD investigation of the effect of particle sphericity on wellbore cleaning efficiency during oil and gas drilling

In all drilling operations in the oil and gas industry, the generation and eventual distribution of founation rock cuttings along the wellbore constitutes a major concern to operational feasibility and profitability. The nature of the annular geometry/wellbore trajectory, rheological properties of the non-Newtonian carrier fluid and physical properties of the cuttings are also very important to consider, particularly in the design stage. Cuttings encountered in practical operations are hardly of a perfectly spherical geometry; however, the ease of mathematical description due to this simplifying assumption is prevalent in most CFD modelling studies. This decreases the accuracy of simulated flow behaviour as far particle-particle and particle-fluid interactions are concerned. We address this challenge by modifying the Syamlal-O'Brien (SO) interphase exchange coefficient in the Eulerian-Eulerian model. This modification yields a better representation of the actual flow dynamics during cuttings transport. Our results show increased transport velocity of non-spherical particles compared to particles of perfectly spherical shape. The relatively complex wellbore geometry (in deviated drilling) considered reveals a key finding: there is greater particle deposition at the inclined-to-vertical (upper) bend, relative to other sections in the CFD flow domain.