Page 238 - Air and Gas Drilling Manual

5-80 Air and Gas Drilling Manual
ε
= 0 949
.
v
˙
From Equation 4-39, the actual shaft horsepower, W , required by each compressor
as
is
W ˙ = 69 .4
as
09
(. ) (. 0949 )
W ˙ as = 81 .2
The above determined 81.2 horsepower is the actual shaft power needed by the
compressor to produce the 34.9 psia pressure output at the surface location elevation
of 2,000 ft above sea level. At this surface location, the input horsepower available
from the prime mover is a derated value (derated from the rated 760 horsepower
available at 900 rpm). In order for the compressor unit to operate at this 2,000 ft
surface location elevation, the derated input power available must be greater than the
actual shaft power needed. Figure 4-15 shows that for 2,000 ft elevation the input
power of a turbocharged prime mover must be derated by approximately 5 percent.
˙
The derated input horsepower, W , available from the prime mover is
i
.
W = 760 1( − 0 05)
i
˙
W = 722 .0
i
For this example, the prime mover of the compressor unit derated input power is
greater than the actual shaft horsepower needed, thus, the compressor unit can be
operated at this 2,000 ft surface location elevation.
Illustrative Example 5.6b Select the appropriate compressor system for the
reverse circulation drilling operation data given in Illustrative Example 5.6a. 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 5.6a it was
found that the drilling location adjusted minimum volumetric flow rate for the 5 7/8
inch diameter, 1,200 ft deep borehole was 280 acfm (for the surface drilling location
of 6,000 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 1,200 ft.
This shallow drilling operation does not require the use of a double drilling rig.
Therefore, the most appropriate drill rig for this drilling operation appears to be the
portable Tamrock Driltech Model D25K drilling rig (see Figure 4-19). This drill rig
has an on-board primary compressor. The compressor is a Sullair Model 840, two-
stage, oil flooded, rotary helical lobe (screw). This compressor is powered by a
Caterpillar Model 3406, diesel fuel, turbocharged prime mover capable of a 400 peak
horsepower at the operating speed of 1,800 rpm (see Figure 4-20). The compressor is
capable of producing a volumetric flow rate of 840 scfm and a fixed pressure of 340