BAKER HUGHES - Drilling Fluids Reference Manual

HYDRAULICS
each portion of the circulating system vary from one part to the other. If the volumetric flow rate
through the circulating system remains constant, then the speed or velocity of the drilling fluid
changes in relation to the cross-sectional area for that particular part of the system. The highest
velocities occur where the diameter is the smallest. The fluid velocity is the first and most
important step in making hydraulic calculations in the drilling operation.
For fluid velocity in the drill string,
where:
V
0.408Q
p = -----------------
D 2
V p = fluid velocity in pipe, ft/sec
Q = volumetric flow rate, gal/min
D = inside diameter of the pipe, in.
For fluid velocity in the annulus,
V
0.408Q
a = -----------------------------------
(D 2 ) 2 – ( D
2 1 )
where:
V a = annular velocity, ft/sec
Q = volumetric flow rate, gal/min
D 2 = hole diameter, in.
D 1 = outside diameter of the drill pipe/collar/etc, in.
Note that the above equations describe average flow rate in the drill string and the annulus. In the
annulus on a directional well there will be a series of velocities in the annulus. Figure 9-9
illustrates the fluid velocity distribution in an eccentric annulus with a rotating inner cylinder.
This is the type of flow pattern to be expected in a deviated well.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 9-10