Flow of Drilling Fluids Through Eccentric Annuli

Abstract

ABSTRACT The eccentric annular flow of power-law and Bingham plastic fluids is analysed in this paper using a new method in which an eccentric annulus is represented by infinite concentric annuli with variable outer, radii. For the case of power-law fluids, analytical solutions of the shear stress and velocity profiles have been obtained which are valid over the entire eccentric annulus. For Bingham plastic fluids, the profiles have been obtained at the minimum and maximum dimension positions of the eccentric annulus, which are considered to be the important positions for the analysis of cuttings transport in an inclined eccentric drilling annulus. The results show that the local velocity and shear stress have greater magnitude in the enlarged region of an eccentric annulus than in the reduced region. In addition, like the case of concentric annular flow, the present analysis indicates that the profiles of the velocity and the magnitude of the shear stress in an eccentric annulus are not symmetric in the radial direction. Previous studies gave either unrealistic symmetric profiles or very complicated solutions. Based on the above analysis, the effect of the eccentricity of a drilling annulus on cuttings transport is evaluated. The results of this analysis will aid in the design of drilling programmes, particularly for deviated wells, to ensure efficient transport of drilled cuttings.