BAKER HUGHES - Drilling Fluids Reference Manual

HYDRAULICS
The ability of a drilling fluid to lift cuttings is affected by many factors, and there is no universally
accepted theory which can account for all observed phenomena. Some of these parameters are fluid
density and rheological properties, annulus size and eccentricity, annular velocity and flow regime,
pipe rotation, cuttings density, and size and shape of the cuttings.
Figure 9-10 shows some general features of cuttings transport in laminar flow. If the particles are
of irregular shape, they are subjected to a torque caused by the shearing of the fluid. If the drillpipe
is rotating, a centrifugal effect causes particles to move toward the outer wall of the annulus in
straight holes and helps keep cuttings moving, which minimizes the cuttings bed in horizontal
holes. Nonetheless, cuttings transport rates are strongly dependent on particle size and shape,
which, during a drilling operation, are both irregular and variable.
The only practical way to estimate cuttings transport or slip velocity of cuttings is to develop
empirical correlations based on experimental data. Even with this approach, there is quite a wide
disparity in the results obtained by different authors.
Particle slip velocity calculations are based upon particle Reynolds Numbers, drag coefficients, and
size of cuttings. Simplifications are made that allow the slip velocity to be determined.
Figure 9 - 10 Cuttings Transport
ADVANTAGE SM Engineering is the recommended tool for conducting hole cleaning simulations
and calculations. The discussion below describes some of the theories involved in cuttings
transport.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 9-24