Page 372 - Air and Gas Drilling Manual

Chapter 8: Air, Gas, and Unstable Foam Drilling 8-55
Drilling at 10,000 ft of depth, the injection pressure is approximately 294 psia.
For this combined primary and booster compressor system, the maximum pressure
the booster can attain is limited by the prime mover power capability. Therefore, it
is necessary to assess whether the prime mover of this unique combined compressor
system has the power to operate at the 4,000 ft surface elevation and produce the 294
psia injection pressure output required to drill at 10,000 ft of depth. The prime
mover for this combined primary and booster compressor system is a diesel fueled,
turbocharged, Caterpillar Model 3412 with a peak output of 740 horsepower at 1,800
rpm (at API standard conditions) (see Section 4.7 in Chapter 4). The theoretical
˙
shaft horsepower, W , required by each of the two compressor units is obtained from
s
Equation 4-35a.
Primary Compressor
The primary compressor is a single-stage rotary screw compressor which has a fixed
pressure output rated at ASME standard atmospheric conditions of 190 psig. ASME
standard atmospheric pressure is 14.7 psia. Thus, the input pressure, p 1s, is
p s 1 = 14 7 psia
.
The output pressure, p 2s, of the primary compressor at the ASME standard
conditions is
p s 2 = 190 + p s 1

.
p = 204 7 psia
s 2
The fixed compression ratio for this single-stage primary, r sp, is
p s 2
r sp =
p s 1

.
r sp = 204 7
.
14 7
.
r = 13 9
sp
The derated pressure output, p 2d, of this primary compressor when operated at 4,000
ft of surface location elevation will be
p 2 d = r sp p at

where p a, is the actual atmospheric pressure at the surface location elevation. The
above becomes

p 2 d = (. 12 685)
13 9) (.