Page 197 - Air and Gas Drilling Manual

79
.6
W
09
W ˙ ˙ as = (. ) (. 0903 ) Chapter 5: Shallow Well Drilling Applications 5-39
.0
= 98
as
The above determined 98.0 horsepower is the actual shaft power needed by the
compressor to produce the 80.7 psia 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 270 horsepower
available at 1,000 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 prime mover is
i
W = 270 1( − 0 148)
.
i
˙
W = 230 .0
i
For this example, the prime mover’s derated input power is greater than the
actual shaft horsepower needed, thus, the compressor system unit can be operated at
this 6,000 ft surface location elevation.
Illustrative Example 5.3b Select the appropriate primary compressor system
for the direct circulation drilling operation data given in Illustrative Example 5.3a.
This selection will give the actual volumetric flow rate of air to be delivered to the
drilling operation. The selection of the appropriate compressor will be made from
the example compressor systems listed in Section 4.7 of Chapter 4. In Illustrative
Example 5.3a it was found that the drilling location adjusted minimum volumetric
flow rate of air for the 6 1/4 inch diameter, 2,400 ft deep borehole was
approximately 930 acfm (for a surface drilling location of 4,000 ft above sea level).
Also determine the injection pressure, the input power required by the compressor,
and the derated output power available from the prime mover while drilling at 2,400 ft.
This depth of borehole will have to be drilled with a drilling rig like that shown
in Figure 1-4. A stand alone compressor unit or units must be used to provide the
compressed air. The skid mounted primary Gardner Denver Model WEN, two-stage,
reciprocating piston compressor is 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 4,000 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 4,000 ft surface elevation is 700 acfm (see Chapter 4).
This volumetric flow rate is not greater than the required adjusted minimum
volumetric flow rate of 930 acfm, thus, two of these compressors must be used.