Page 190 - Air and Gas Drilling Manual

5-32 Air and Gas Drilling Manual
˙
= 193
.2
W
as
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
˙
W = 340 .8
i
For this example, the prime mover’s derated input power is greater than the
actual shaft horsepower needed, thus, the compressor system can be operated at this
6,000 ft surface location elevation. This particular example is somewhat
complicated since the prime mover for this integrated compressor unit shares its
power with other auxiliary equipment on the portable drilling rig. Thus, a portion
of the 340.8 horsepower available from the prime mover will be used by the
hydraulic rotary head unit. To get a complete assessment of the power available to
this compressor these additional power needs should be evaluated.
b) Gardner Denver Model WEN Reciprocating Piston Primary Unit.
If the drilling rig used for this drilling operation does not have an on-board
compressor system (see Figure 1-4), then a stand alone compressor unit must be
used to provide the compressed air. A candidate stand alone primary compressor
system is the skid mounted primary Gardner Denver Model WEN, two-stage,
reciprocating piston compressor powered by a Caterpillar Model D353, diesel fueled,
turbocharged, prime mover capable of a 270 peak horsepower at the operating speed
of 1,000 rpm (see Figure 4-22). This compressor is capable of producing a
volumetric flow rate of 700 scfm and a maximum pressure of 350 psig at API
standard conditions. When this compressor unit is to be placed at the 6,000 ft
surface elevation drilling location, the compressor will still produce the same
volumetric flow rate as at sea level conditions. Thus, the actual volumetric flow rate
of this compressor at the 6,000 ft surface elevation is 700 acfm (see Chapter 4).
This volumetric flow rate is greater than the required adjusted minimum volumetric
flow rate of 481 acfm (factor of safety of 1.46). Therefore, this compressor unit is
capable of producing the volumetric flow rate to drill the borehole.
A comparison must be made between the injection pressure required to drill this
borehole and the pressure capability of the selected compressor system. The
injection pressure is obtained by calculating through a sequence of steps that
determine the bottomhole pressure in the annulus, the pressure at the bottom of the