Page 339 - Air and Gas Drilling Manual

8-22 Air and Gas Drilling Manual
Illustrative Example 8.3b Determine the bottomhole and injection pressures
while drilling at 10,000 ft of depth for the drilling operations described in
Illustrative Examples 8.2 and 8.3a. Compare the injection pressure to the maximum
pressure capability of the selected semi-trailer mounted Dresser Clark Model CFB-4,
four-stage, reciprocating piston compressor. Also, determine the horsepower
required by the compressor and the maximum derated horsepower of the Caterpillar
Model D398 prime mover. Compare the compressor required horsepower and the
maximum derated horsepower from the prime mover.
General Data
Table 4-1 gives an average atmospheric pressure of 12.685 psia for a surface
location of 4,000 ft above sea level (mid latitudes North America) (also see
Appendix D). The actual atmospheric pressure for the air at the drilling location
(that will be utilized by the compressor), P at, is
.
p at = 12 685 psia
P at = p 144
at
2
,
P at = 1 827 lb/ft abs
The actual atmospheric temperature of the air at the drilling location (that will be
used by the compressor), T at, is
o
t at = 60 F
.
T = t + 459 67
at at
o
T at = 519 67 R
.
Thus, P g and T g become

P = P at = 1 827 lb/ft abs
2
,
g
o
T = T at = 519 67 R
.
g
Using Equation 4-11, the specific weight of the gas entering the compressor is
(1 827, ) (1 0. )
γ =
g
(53 36. ) (519 67. )
γ g = 0 0659 lb/ft 3
.