Page 522 - Air and Gas Drilling Manual

V
.
sfa4
Using Equation 6-89 the Reynolds number of the foam as it exits this openhole
annulus section is 681 ft/sec Chapter 10: Stable Foam drilling 10-47
V sfa4 D h D 3
N Rsfa4
sfa4
81
0
6
(. ) ( .656 . 0 552 )
N Rsfa4
. 0 00009242
N Rsfa4 7 679
,
The Reynolds number calculation above is greater than 4,000. This indicates that
the flow condition is turbulent. Therefore, the empirical von Karman equation (i.e.,
Equation 6-92) must be used to determine the Fanning friction factor for the foam
flow in this annulus section.
The surface roughness for the inside wall of a borehole in the example sandstone
and limestone rock sequence, e oh, is
e oh 001 ft
.
The inner surface of this annulus section is the outer surface of the drill pipe tool
joint lumped geometry has the surface roughness of commercial steel pipe, e p. The
surface roughness of commercial steel pipe is

.
e 0 00015 ft
p
Thus, using Equation 8-2, the average absolute surface roughness of this annulus
section, e av4, is

001)
0 552)
0 00015)
0 656)
(. (. 2 (. (. 2
4 4
e av4
(. 2 (. 2
0 552)
0 656)
4 4
.
e av4 0 0059 ft
Therefore, Equation 6-92 becomes