Hydrodynamics of Off-Bottom Plug Placements in Deviated Wells

Abstract Wellbores come in various shapes, from vertical to deviated and horizontal configurations. Deviated or horizontal wells typically involve a vertical drilling phase before shifting towards the target direction. As oil and gas production becomes economically unviable, well abandonment is common, involving the deployment of multiple cement plugs. The off-bottom plugs, located above the lowermost plug, are strategically placed in the vertical or least deviated sections of the well. We consider a representative 2D model for the early stages of cement placement, where slurry is injected from a concentric injector with the well, and explore the influence of well inclination on the placement process. In vertical wells, the injected fluid forms a central finger below the injector. However, in highly deviated wells, the fluid slumps towards one side of the casing walls. The transition between these two flow regimes occurs through a monotonic change with the inclination angle. In all cases, the buoyancy-driven flow is disrupted, resulting in a mixed layer below the injector, and the accumulation of the injected fluid above it. While the accumulated fluid remains primarily unmixed with wellbore fluids in vertical wells, intermittent mixing occurs in deviated wells. The frequency and magnitude of this mixing change non-monotonically with the inclination angle.