Page 517 - Air and Gas Drilling Manual

10-42 Air and Gas Drilling Manual
.
0 00007784
sfa3
0 529
.
ft 2
.
0 0001475
sfa3
sec
The average velocity of the foam as it exits this openhole annulus section is
P T
at av3
Q g Q w
P a2 T at
V sfa3
D h 2 D 2 2
4
,
.
1 826 6 . 586 29
( 27 64) 0 234
.
.
78 039 4 . 519 67
.
.
V sfa3
.
0 656 2 0 375 2
.
4
.
V 423 ft/sec
sfa3
Using Equation 6-89 the Reynolds number of the foam as it exits this openhole
annulus section is
V sfa3 D h D 2
N Rsfa3
sfa3
0
(. ) ( .656 . 0 375 )
4
23
N Rsfa3
. 0 0001475
,
N 8 088
Rsfa3
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 surfaces of this example openhole annulus section has two different surface
roughness. The inside surface of this openhole borehole is a wall drilled in a
sandstone and limestone rock sequence. Unless such a rock sequence is highly
fractured, the inside surface of the openhole borehole approximates the inside surface
of a concrete water pipe used in community water systems. Table 8-1 correlates the
borehole inside surface roughness for a variety of rock formation types with the