An experimental study of displacement flows in stationary and moving annuli for reverse circulation cementing applications

Abstract

We present an experimental study of buoyant displacement flows in vertical narrow centric/eccentric annular configurations, representing the oilfield primary cementing process, from a fluid mechanics perspective. In this study, we consider the reverse circulation cementing case, i.e. the case in which the cementing fluids are pumped down from the surface into the annulus and the in-situ fluids are taken through the casing or tubing. The fluid proxies used to represent the industrial fluids are miscible, with different rheological behaviours, i.e. salt-water (Newtonian), Xanthan (shear-thinning) and Carbopol (viscoplastic) solutions, and they have various density contrasts. Our dimensional analysis and systematic simplifications allow us to describe the flow using five dimensionless numbers: m (viscosity ratio), Fr (densimetric Froude number, quantifying effects of the density difference or buoyancy), Re (Reynolds number, quantifying the effects of the imposed flow rate), e (eccentricity) and f (reciprocation frequency). We examine the effects of the aforementioned parameters in stationary and moving annuli, wherein we change the frequency of the inner pipe reciprocation motion, over a fixed amplitude. Using mainly high-speed camera imaging techniques, we analyse displacement flow patterns and mixing between the fluids. We show that the density-stable or density-unstable configurations, the non-Newtonian effects, and the annulus eccentricity exert a significant impact on the displacement flow features, which we explain through a detailed comparison between Newtonian and non-Newtonian displacements. In addition, we demonstrate that an interplay between the yield stress and the annulus motion can remarkably change the displacement flow behaviour, particularly the wall residual layer thicknesses of the displaced fluid. Finally, we quantify the effects of different flow parameters on the leading front velocity, representing the displacement efficiency in the reverse circulation cementing.