Turbulent displacement flows of viscoplastic fluids in obstructed eccentric annuli: Experiments

Abstract

We present an experimental study of turbulent displacement flows in eccentric annuli, where the displacing fluids are water, 0.1% and 0.2% xanthan gum solutions, and the in situ fluid is a viscoplastic, 0.15% Carbopol solution. We focus on the effect of a solid obstruction on the narrow side of the annular gap, analogous to a consolidated cuttings bed in well cementing operations. For comparison we include experiments with an unobstructed test section with eccentricity e set at ∼0.5. While the displacement flow is successful without the obstruction regardless of the displacing fluid, we find that the obstruction at e∼0.5 is mostly detrimental to removal of the yield stress fluid stuck downstream of it, and a decrease in Reynolds numbers via formulation of xanthan gum solutions contribute to a less effective displacement in all situations due to the decrease in fluctuating stresses. Upstream of the obstruction, we observe complete removal of the Carbopol, likely due to enhanced vorticity effects. However, at high eccentricity values of e∼0.7, the effect of the obstruction on the displacement of Carbopol appears to be negligible, especially in the less turbulent situations with the xanthan gum solutions where the stationary Carbopol layer covers the entirety of the solid blockage, both upstream and downstream. Thus, in a highly eccentric obstructed annulus, the eccentricity remains the dominant factor to hinder the displacement.