Page 245 - Air and Gas Drilling Manual

Chapter 5: Shallow Well Drilling Applications 5-87
=
p
284 1 psia
.
d2
The above compressor derated pressure of 284.1 psia is greater than the injection
pressure of 94.1 psia, therefore, the compressor is capable of producing the injection
pressure needed for this example drilling operation.
The last criteria to check 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). The theoretical shaft horsepower, W ,
s
required by the compressor is obtained from Equation 4-35a. Equation 4-35a
becomes
 (. ) 
04
() ( . ) (.769 ) (840 )   284 1 ()( . )
1 4
11
. 
2
4
21
W = − 1 
˙
s
04
(.) 229 .17   11 .769  
 
˙
W = 173 .9
s
Assuming a mechanical efficiency, ε , is
m
ε = 090
.
m
˙
From Equation 4-39, the actual shaft horsepower, W , required by the compressor
as
is
W ˙ as = 173 .9
. 09
W ˙ as = 193 .2
The above determined 193.2 horsepower is the actual shaft power needed by the
compressor to produce the 284.1 psia fixed pressure output at the surface location
elevation of 6,000 ft above sea level. At this surface location, the input horsepower
available from the prime mover is a derated value (derated from the rated 400
horsepower available at 1,800 rpm). In order for the compressor system to operate at
this 6,000 ft surface location elevation, the derated input power available must be
greater than the actual shaft power needed. Figure 4-15 shows that for 6,000 ft
elevation the input power of a turbocharged prime mover must be derated by
˙
approximately 14.8 percent. The derated input horsepower, W , available from the
i
prime mover is
(
. )
˙
W = 400 1 − 0 148
i