An experimental study of cuttings transport in directional wells

This paper contains a comprehensive discussion of a large-scale study of cuttings transport in directional wells. Previous investigators used unrealistically high fluid velocities and/or short test sections where steady-state conditions had not been established. For this study, a 40-ft test section was used. Pipe rotation and eccentricity as well as several types of drilling muds and flow regimes were studied. Annulus angles varied from zero to 90 degrees and actual drilled cuttings were used. Results indicate that the major factors affecting cuttings transport are drilling fluid velocity, hole inclination and fluid rheological properties. Much higher annular velocities are required for effective hole cleaning in directional wells than in vertical wells. An increase in hole angle and/or drilling rate reduces the transport performance of drilling fluids. Hole angles of 40 to 50 degrees are critical due to a combination of cuttings buildup and downward sliding of the bed of cuttings. High-viscosity muds were observed to provide better transport than low-viscosity muds.