In completion of oil and gas wells, zonal isolation requires proper cement placement with adequate bonding to the casing and formation. To achieve a successful cementing operation, the cement slurry should be properly designed to enable effective displacement of the drilling fluid from the annulus between the casing and wellbore. This is a complex process, involving displacement of viscoplastic fluids in eccentric annuli. The rheology, flow rate, and interfacial mixing of these fluids have direct impact on the displacement efficiency. Reliable computational modeling of the dynamics of the displacement process is beneflcial to properly perform pre-job design and post-job analysis of the cementing operation. Furthermore, experimental data are also used to validate numerical predictions. This paper presents a flow visualization study using a helical flow device with adjustable annular eccentricity and rotation of the inner cylinder. Displacement experiments were conducted with a variety of non-Newtonian fluids to simulate the cement slurry -drilling mud displacement process.