Hole Cleaning in Large, High-Angle Wellbores

ABSTRACT Beds of cuttings are usually formed on the bottom of large, high-angle wellbores during drilling. When the drill string is moved axially along the wellbore, large bottom-hole assembly elements such as drill bit and stabilizers tend to plow the cuttings bed, thereby causing the formation of plugs of cuttings which give rise to high overpulls, loss of circulation, continuous need for operations such as backreaming, and stuck pipe. To reduce the likelihood of these costly hole problems occurring, it is necessary to minimize the height of the cuttings bed which forms while drilling, and to minimize the tendency of the bottom-hole assembly to form plugs of cuttings. This can be done with a new hole cleaning tool described in this paper. This tool was developed using a combination of analytical modeling based on fluid mechanics first principles, experimental data, and field data. The tool enables establishment of pump flow rates, drilling fluid rheological properties, drill string configurations, and well profiles for minimal risk of experiencing problems associated with the existence of a cuttings bed.