Page 526 - Air and Gas Drilling Manual

.
0 00006943
sfa5
.
0 773
ft 2 Chapter 10: Stable Foam drilling 10-51
.
0 00008986
sfa5
sec
The average velocity of the foam as it exits this openhole annulus section is
P at T av5
Q g Q w
P a4 T at
V sfa5
D h 2 D 2 4
4
1 826 6 . 601 91
.
,
.
.
( 27 64) 0 234
,
137 281 519 67
.
V sfa5
.
.
0 656 2 0 563 2
4
.
V sfa5 735 ft/sec
Using Equation 6-89 the Reynolds number of the foam as it exits this openhole
annulus section is
V sfa5 D h D 4
N Rsfa5
sfa5
0
(. ) ( .656 . 0 563 )
7
35
N Rsfa5
. 0 00008986
N Rsfa5 7 672
,
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 inside surface of borehole roughness for a variety of rock formation types
with those of known engineering pressure conduits. From this table 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