Displacement flows in eccentric annulus : methods to improve displacement efficiency

This thesis presents a study of displacement flows in highly deviated and horizontal eccentric annuli with the objective of increasing the displacement efficiency. The motivation for studying these types of flows comes from primary cementing, where a sequence of fluids is pumped into the well to displace in-situ drilling mud and to provide a hydraulic seal in the annulus, between wellbore and casing. With horizontal wells becoming increasingly more common, properly cementing such wells is far more challenging, which has resulted in a recent trend of increasing wellbore leakages. Eccentricity distorts the flow profile in the annular gap and horizontal wells are often highly eccentric. We adopt the mathematical model to simulate a realistic well to analyze common cementing practices. By pumping excess cement volume, gradual removal of residual mud is observed as long as the mud is yielded. Increasing centralizer usage shows improved eccentricity which in turn results in improved displacement with decreased residual mud. Performing staged cementing allows flexibility in both managing frictional pressure and designing flows for vertical and deviated sections separately. An experimental approach is used to study the effects of inner cylinder rotation. Changes in flow behavior are observed with rotation, depending on the balance between buoyancy and rotational stresses. When eccentricity is sufficiently high, flow separation occurs in the wide gap, at the top of the annulus. The displacing flow is contained in the recirculatory zone. Casing rotation allows for complete removal of the bottom side residual layer by forcefully creating azimuthal flows in the narrow gap. Rotation shows increased displacement efficiency in most cases and steady displacements are still possible. The results of the study recommend increasing the amount of excess volume and centralizer usage, performing staged cementing, and adding casing rotation to improve the displacement flow. We emphasize the importance of managing eccentricity for a successful cement placement. A proper design of centralizer selection and placement is outside the scope of this thesis, but becomes a priority in addition to the methods presented above.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat