A Theoretical and Experimental Study of the Role of Taylor Vortices In the Transport of Drill Cuttings

by
Zeno George Philip, MSE

University of Texas at Austin, 1997
Supervisor: Mukul M. Sharma
Martin E. Chenevert

Taylor vortices, i.e., toroidal rings, are formed in an annulus when one pipe is rotated inside another. These rings form when the critical rotation rate (rpm) is reached. Equations are presented to calculate the critical rpm above which Taylor vortices form for both Newtonian and power law fluids with axial flow. The theoretical computations show that under typical drilling rotation rates Taylor vortices do form.

Experiments were conducted with a wide range of Newtonian and power law (shear-thinning) fluids in a transparent annular geometry. The experimental values of critical rpm are in agreement with computed ones. The experiments also clearly show the existence and structure of Taylor vortices. These vortices may play an important role in the transport of drill cuttings -- especially in horizontal wells.

For Newtonian fluids, the cuttings lifting capacity increases with fluid viscosity. For power law (shear thinning) fluids, however, contrary to expectation, the particle lifting capacity decreases with increasing apparent viscosity. This is probably due to differences in the shape of the velocity profiles for Newtonian and power law fluids. Higher velocities close to the stationary walls are obtained with Newtonian fluids as compared to shear-thinning fluids.

Visual observations of the cuttings bed clearly show the effects of fluid rheology and rotation speed on the formation and impact of Taylor vortices on cuttings transport. The overall lift experienced by the cuttings is due to the resultant of the vortex, azimuthal and linear velocities.

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