Page 631 - Air and Gas Drilling Manual

Chapter 11: Specialized Drilling Equipment 11-69
2
2 635)
.
0 016
53 36
.
b
i1
2
232 2 . )
10 .
(
0 319)
4 (. (. 2 5
,
b i1 2 486
Equation 6-72 becomes
. 05
2 (. 0 019 ) ( , 6 650 )
(,370 ) 2 ( , 2 486 ) (537 .66 ) 2 e 537 .66 1
61
P in 2 (. 0 019 ) ( , 6 650 )
e 537 .66
2
,
P in 51 340 lb/ft abs
P in
p in
144
p in 356 5 psia
.
The injection pressure given above is the flowing air pressure at the top of the
lumped drill pipe body length inside the drill string in the cased section of the
borehole while drilling at a depth of 10,000 ft. This is the approximate injection at
the top of the drill string required to force a volumetric flow rate of 2,400 acfm
through the circulation system. This injection pressure is the pressure the
compressor output must match.
Compressor Unit Prime Mover Capability
Knowing the injection pressure, it is necessary to ascertain whether the prime
mover of this primary compressor unit has the power to operate at the 4,000 ft
surface elevation. The prime mover for this compressor is a diesel fueled,
turbocharged, Caterpillar Model D398 with a peak output of 760 horsepower at 900
rpm (at API standard conditions) (see Section 4.7 in Chapter 4). The theoretical
˙
shaft horsepower, W , required by each of the two compressors is obtained from
s
Equation 4-35a. Equation 4-35a becomes
, 2 400
04
12
(.685 ) (. )
4
() ( . ) 4 2 356 .5 ()( . )
1
41
4
W ˙ s 1
(.) 229 .17 12 .685
04
W ˙ s 250 .2