Fiber Sweeps for Hole Cleaning

Abstract

Summary Cuttings transport in highly deviated wellbores is more challenging and critical than in vertical wells. In inclined wells, the fluid velocity has a reduced vertical component that may not be sufficient to transport all the cuttings to the surface. When cuttings returns do not appear to be sufficient for the drilling rate, hole-cleaning sweeps are applied to clean the borehole or reduce cuttings-bed thickness. Fiber-containing sweeps have been very effective in cleaning highly deviated and extended-reach wells. In addition, substantial torque and drag reduction has been reported when fiber-containing drilling fluids are used in the field. Although field observations are encouraging, very little is known currently about flow behavior, hydraulics, and cuttings-transport efficiency of fiber sweeps. There is a great need for understanding how fiber particles enhance the cleaning capabilities of fiber-containing sweeps. The interaction between fiber particles and drilling fluid is still not understood fully, although the improvement in cuttings and solids transport is attributed to the formation of a fiber mat network that enhances the carrying capacity of drilling fluids. This article presents results of experimental investigations conducted to study hole-cleaning performance of a fiber sweep. Flow-loop experiments have been carried out to evaluate and compare sweep efficiencies of the fiber sweep [0.47% Xanthan gum (XG) and 0.04% synthetic fiber] and the base fluid (0.47% XG). Equilibrium bed heights were measured at different sweep flow rates in horizontal and inclined configurations. Results from this study indicate that a fiber-containing sweep has better hole-cleaning capabilities than the base fluid, even though these two sweep fluids have very similar rheological properties. Moreover, adding fiber slightly reduces annular pressure loss at the same average bed height.