Page 189 - Air and Gas Drilling Manual

354 696
r =
c
14 696
r = 24 14. . . Chapter 5: Shallow Well Drilling Applications 5-31
c
The approximated derated output pressure, p d2, for this compressor when placed at a
6,000 ft surface drilling location is determined from
p d2 = r p at
c
where p at is the actual atmospheric pressure at the 6,000 ft surface drilling location
(i.e., 11.679 psia). Thus, the derated output pressure, p d2, is
11 769)
p = ( 24 14) ( .
.
d2
p d2 = 284 1 psia
.
The above compressor derated pressure of 284.1 psia is greater than the injection
pressure of 96.2 psia, therefore, the compressor is capable of producing the injection
pressure needed for this example drilling operation.
The last criteria to consider is whether the prime mover has the power to operate
at the 6,000 ft surface elevation. The prime mover for this compressor is a diesel
fueled, turbocharged, Caterpillar Model 3406 with a peak output of 400 horsepower
at 1,800 rpm (at API standard conditions) (see Section 4.7).
˙
The theoretical shaft horsepower, W , required by the compressor is obtained
s
from Equation 4-35a. Equation 4-35a becomes
 (. ) 
04
2
11
1 4
() ( . ) (.769 ) (840 )   284 1 ()( . ) 
. 
4
21
˙
W = − 1
s
(.) 229 .17   11 .769  
04
 
˙
W = 173 .9
s
Assuming a mechanical efficiency, ε , is
m
ε m = 090
.
˙
Then from Equation 4-39, the actual shaft horsepower, W , required by the
as
compressor is
W ˙ as = 173 .9
. 09