Abstract
In a horizontal well drilling operation, a part of generated drill cuttings tends to settle down at a lower annular section. Formation of sand bed causes several operational issues such as low rate of penetration and stuck drill pipe. In this study, a lab-scale experimental work is carried out to investigate hole cleaning in the extended reach and horizontal drilling operation. This work focuses on the visualization of the flow behaviour of drill cuttings in the horizontal annular section. A 6.16 m-long horizontal well test section with an outer diameter of 4.5 inch (11.43 cm) and an inner diameter of 2.5 inch (6.35 cm) is used in this study. Four non-Newtonian Herschel-Bulkley fluids are tested as the drilling mud. Solid glass beads of 2.5–3.0 mm with a density of 2650 kg/m3 are utilized as the drill cuttings with two different solid concentrations. The flow behaviour in the horizontal annular section is analyzed with a high-speed imaging technology at 2000 frames/second and electrical resistance tomography (ERT) technique. The effects of fluid rheology, fluid velocity, drill pipe rotation, and eccentricity on the cuttings transport are investigated. This study showed that an optimum drill pipe rotation of 80 RPM and a minimum transport performance number (TPN) of 70 is required for efficient hole cleaning in horizontal well section. This study also reveals that fluid rheology has a significant effect on the minimum transport velocity (MTV). A flow regime analysis revealed that a turbulent flow regime is required for effective hole cleaning without sand bed formation. The mechanistic three-layer model of cuttings transport is experimentally verified with high-speed visualization techniques. Furthermore, this study introduces the concept of estimating the instantaneous annular solid volume fraction by the ERT system as well as visualization of solid bed distribution in the annulus section.
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