In the case of deviated, horizontal, extended reach and multi-lateral wells, the existence of a particle bed and also the formation of a partially or completely buried cuttings bed can be problematic for borehole cleaning. As a solution increasing the drilling fluid velocity can help in eroding the deposited bed substantially above a critical velocity, which depends on several flow parameters. For instance pipe rotational speed can enhance particle transportation at flow velocities lower than the critical annular fluid velocities as reported in the literature. The consequences of pipe rotation on the fluid transport ability are also subject to the inclination of the drilled section. The present paper discusses the results of numerical simulations of water based drilling fluid flows regarding the inclination effect, the fluid viscosity, the clearance between the pipe and the borehole and the resulting pressure losses.

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