Experimental and Numerical Analysis of Fluid Displacement Efficiency in Vertical Primary Cementing: Impact of Flow Regime, Rheological Properties, and Eccentricity

Abstract Efficient fluid displacement during primary cementing is critical for well integrity and zonal isolation. This study investigates multiphase flow dynamics in annular and tubular geometries, with a focus on density and viscosity ratios, flow regimes, and eccentricity. Large-scale experiments were conducted complemented by 3D numerical simulations. The goal is to assess displacement efficiency, quantify residual films associated to eventual stagnant regions, and analyze fluid interface behavior under field-representative conditions. Experiments were conducted in a custom 14.4 m vertical test unit, equipped with pressure, density, and flow rate sensors. Tests included upward/downward flows and concentric/eccentric setups using Newtonian and non-Newtonian fluids under laminar and turbulent conditions. Density and viscosity ratios were varied to evaluate their effects on displacement. Displacement efficiency was determined with pumped volume and residual fluid measurements. Parallel CFD simulations in OpenFOAM replicated experimental conditions, using mesh refinement, k–ω SST turbulence modeling, and convergence checks. CFD outputs pressure drop, volumetric fractions, and interface dynamics—were validated against experimental results to confirm the accuracy and robustness of the model. Experimental and CFD results demonstrated strong agreement across variety of flow conditions. In upward flows, a displacing-to-displaced fluid density ratio greater than one consistently led to near-complete displacement, while lower density ratios (Rd < 1) introduced flow instabilities and reduced displacement efficiency. Discrepancies between internal volume fractions and outlet compositions suggest the presence of displacing fluid fingering. Turbulent flow mitigated the negative effects of low Rd and eccentricity, improving efficiency compared to laminar flow. Viscosity ratio exhibited a secondary effect: higher viscosity ratios helped stabilize the two-fluid interface and improved efficiency when Rd > 1. Eccentricity significantly influenced displacement in laminar flow, especially with Rd < 1, though differences between intermediate (0.17) and severe (0.6) eccentricities were minor. Emulsion formation from specific fluid formulations increased residual displaced volumes in some cases. Residual films and partial mixing were quantified, and CFD accurately captured these behaviors. These findings highlight the importance of designing fluids with favorable density and viscosity ratios, operating in turbulent regimes when possible, and minimizing eccentricity or compensating for it through fluid properties. CFD proved effective in predicting complex flow dynamics, supporting its use in planning and optimizing cementing operations under realistic well conditions. This work presents a unique large-scale experimental dataset with hydrodynamic similarity, including annular and tubular tests using Newtonian, non-Newtonian, and synthetic fluids. Though not used in simulations, synthetic fluids enabled controlled evaluation of interface behavior and residual films. Validated 3D CFD simulations captured effects of non-Newtonian rheology, eccentricity, and density ratio, extending experimental results to real applications where aspect ratios are different. These approaches enhance modeling and support realistic optimization of primary cementing and well-cleaning.