Page 374 - Air and Gas Drilling Manual

The first stage compressor ratio is

.
r sb =  293 9 2 1 Chapter 8: Air, Gas, and Unstable Foam Drilling 8-57
 176 6 . 
r sb = 129
.
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 ) (129 )14 . − 1  


.
.
.
v
  
ε v = 0 949
.
From Equation 4-39, the actual shaft horsepower, W ˙ asb , required by each compressor
is
W ˙ asb = 49 .6
(. 0 90 ) (. 0 949 )
W ˙ asb = 58 .1

The above determined 58.1 horsepower is the actual shaft power needed by the
reciprocating piston booster compressor to produce the 293.9 psia pressure output
(with an input of 176.6 psia from the primary) at the surface location elevation of
4,000 ft above sea level (while drilling at a depth of 10,000 ft).
Total Horsepower of Compressor System
˙
The total actual shaft horsepower, W , needed by the combined primary and
ast
booster compressor system in each unit is
W ˙ ast = W ˙ asp + W ˙ asb

W ˙ ast = 409 .8 + 58 .1

W ˙ ast = 467 .9

At this surface location, the input horsepower available from the Caterpillar
Model 3412 prime mover is a derated value (derated from the rated 740 horsepower
available at 1,800 rpm). In order for the compressor units to operate at this 4,000 ft