Primary Cementing of Horizontal Wellbores With Solid Cutting Beds

Abstract

Abstract We present an experimental and numerical investigation of displacements of viscoplastic fluids in an eccentric, horizontal annulus with a cutting bed left in the well. This problem is of interest to both industrial and academic viewpoints. Firstly, the experiment provides a simplified, analogous effect to a cuttings bed in industrial situations. Secondly, while successful and failed displacements of viscoplastic fluids with various eccentricities have been well documented in the literature, displacements with a blockage in the annular geometry have not been experimentally studied before. We carry out the experiments with a pump driven flow loop with a 7.5m annular test section, with a borosilicate glass outer pipe and stainless steel inner pipe. To model the cutting bed, a solid insert is attached to the narrow side of the annulus. Carbopol solutions, widely known as model yield-stress fluids, are displaced from the blocked annulus. Our protocol consists of direct visualization of the interface between the displaced and displacing fluids with a high-speed camera and UV-lighting setup, along with pressure and flow rate measurements. We compare our experimental data and images with 3D numerical simulations, using a Volume of Fluid method to capture the interface between the fluids. The 3D model provides us with a more detailed analysis of the concentration and velocity profiles, along with comparisons to snapshots of the experimental displacements. The dynamics of the displacement of two fluids in a horizontal circular annulus is governed by buoyancy, eccentricity and the rheology of the fluids. A positive density difference promotes slumping of the displacing fluid towards the bottom of the annulus. Nevertheless, high eccentricity values (e = 1-standoff) are common due to the weight of the casing pulling downwards, opposing the buoyancy force. Finally, the rheology of the fluids is relevant to determine the presence of un-displaced layers of mud, e.g. at the walls. The same competition described above holds true in the annulus with cutting beds. The blockage incorporates an additional way of altering the velocity field around the annulus. Here we show that the blockage can affect the mud removal in the annular space of the well.