Page 237 - Air and Gas Drilling Manual
P. 237
Chapter 5: Shallow Well Drilling Applications 5-79
leading to the top of the borehole annulus and the vent line leading from the top of
the drill string. These losses are not important for shallow drilling operations
(Chapter 8 calculation examples will consider these losses which become important
for deep boreholes). Therefore, the above pressure slightly underestimates the actual
pressure that is seen at the pressure gauge just downstream of the compressor. The
above injection pressure is significantly less than the capability of this reciprocating
piston compressor (i.e., 1,000 psig), therefore, the compressor is capable of
producing the above injection pressure (the maximum pressure capability of a
reciprocating piston compressor is not derated with surface location elevation as long
as the prime mover has the power necessary to produce the required pressure).
The last criteria to check is whether the prime mover of this primary compressor
unit has the power to operate at the 2,000 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). The
reciprocating piston compressor is not limited by its maximum pressure capability
but more by the prime mover capability to produce the power required by the
˙
compressor shaft. The theoretical shaft horsepower, W , required by the compressor
s
is obtained from Equation 4-35a. Equation 4-35a becomes
04
(. )
13
4
() ( . ) (.662 ) (1 200 ) 34 .9 ()( . )
,
1 4
41
4
W = − 1
˙
s
(.) 229 .17 13 .662
04
˙
W = 69 .4
s
The mechanical efficiency, ε , is
m
ε m = 090
.
The first stage compression ratio of the compressor is
1
r = 34 9 . 4
s
.
13 662
r = 126.
s
The volumetric efficiency (only for the reciprocating piston compressor), ε , is
v
determined from Equation 4-38. The compressor clearance volume ratio, c, is
assumed to be 0.06. Equation 4-38 becomes
1
ε = 096 1 − (006 . − 1
.
.
v ) (126 )14 .
