Effects of wellbore irregularity on primary cementing of horizontal wells, Part 2: Small scale effects

Wellbore irregularities turn the narrow eccentric annulus of primary cementing into a fully three-dimensional (3D) flow geometry. Here we explore the effects of coupling the borehole geometry, reconstructed from high frequency caliper data, with 3D computations of the displacement flow. Displacement flows through circular boreholes with enlargements of varying depths and wavelengths tend to result in both enhanced secondary flows and in residual drilling mud. Short wavelength deep enlargements generally have larger percentage of residual mud. We then perform a frequency analysis of typical caliper data from Northwest Canada, showing that the borehole geometry may typically be reconstructed using the lowest 3–5 dominant frequencies. We present example computations of displacement flows through these geometries. Although the underlying dynamics are those of more uniform annuli, these computations do reveal in that small changes in geometric description can lead to noticeable changes in the displacement mechanics, especially in the fluid present at the walls of the annulus. The conclusion is that borehole irregularity can make a significant difference in cementing horizontal wells, which are anyway already troublesome.