Numerical Study on the Transport Characteristics of Discoidal and Cylindrical Cuttings in Non-Newtonian Drilling Fluids

: The application of long horizontal drilling technology in oil and gas engineering significantly increases the effective production area and improves extraction efficiency. However, during the drilling process, the massive deposition of cuttings particles at the bottom of the horizontal annulus readily leads to a series of accidents such as pipe sticking. This study couples computational fluid dynamics and discrete element method to investigate the transport and deposition characteristics of discoidal and cylindrical cuttings with four equivalent diameters in non-Newtonian drilling fluids. The Hertz-Mindlin model is used to describe the interactions between particles. Furthermore, a drag model influenced by sphericity is established between the non-Newtonian fluid and the non-spherical cuttings. Numerical results indicate that the rheology of the shear-thinning drilling fluids, the distribution of strain rate and effective viscosity demonstrates a significant negative correlation. Under stable cuttings transport flow conditions, the spatial distribution of discoidal and cylindrical particles can be divided into suspension, transition, and deposition zones. Smaller cuttings in suspension zone exhibit the maximum average velocity, and larger particles are more likely to deposit at the bottom to form a cuttings bed. Compared with cylindrical particles, discoidal particles exhibit lower sphericity, higher retained volumetric fraction, and lower cuttings transport ratio. Based on the data obtained from numerical studies, a binary quadratic polynomial regression model related to the retained volume fraction of cuttings in the annulus under steady-state and their sphericity and diameter was also established.