Hole Cleaning in Full-Scale Inclined Wellbores

Summary A 4-year multifactor experimental study was completed recently on hole cleaning in inclined wellbores. Ten variables-annular mud velocity, mud density, mud rheology, mud type (oil- or water-based), cuttings size, rate of penetration (ROP), drillpipe rotary speed, drillpipe eccentricity, drillpipe diameter, and hole angle-were studied over a range of values. The full-scale annular test section was 60 ft [18.3 m] long, with 3- and 4.5-in. [76- and 114-mm] drillpipe in an 8-in. [203-mm] ID (wellbore diameter). Hole angle varied from 45 to 90° from vertical. Results frequently showed a large buildup of cuttings in the annulus, and cuttings were difficult to remove once a bed had built up on the low side of the wellbore. Cuttings-bed sliding also was more intense than anticipated. Mud velocity and mud density have the greatest effect on hole cleaning. Several two- and three-factor variable interactions also emerged from a subsequent statistical analysis.