Experimental Study of Cuttings Transport in Directional Wells

Summary A large-scale study of cuttings transport in directional wells is discussed in this paper. Previous investigators used unrealistically high fluid velocities and/or short test sections where steady-state conditions had not been established. This study used a 40-ft [12.2-m] test section. Pipe rotation and eccentricity, as well as several types of drilling muds and flow regimes, were studied. Annulus angles varied from 0 to 90°, and actual drilled cuttings were used. 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° are critical because of cuttings buildup and downward sliding of the bed of cuttings. High-viscosity muds were observed to provide better transport than low-viscosity muds.