Page 367 - Air and Gas Drilling Manual

8-50 Air and Gas Drilling Manual
From Equation 4-39, the actual shaft horsepower, W , required by each compressor
is
W ˙ as = 207 .4 ˙ as
(. 0 90 ) (. 0 922 )
W ˙ = 249 .9
as
The above determined 249.9 horsepower is the actual shaft power needed by
each of the two compressors to produce the 212.4 psia pressure output at the surface
location elevation of 4,000 ft above sea level (while drilling at a depth of 10,000 ft).
At this surface location, the input horsepower available from the Caterpillar Model
D398 prime mover is a derated value (derated from the rated 760 horsepower
available at 900 rpm). In order for the compressor units to operate at this 4,000 ft
surface location elevation, the derated input power available must be greater than the
actual shaft power needed. Figure 4-15 shows that for 4,000 ft elevation the input
power of a turbocharged prime mover must be derated by approximately 10 percent.
˙
The derated input horsepower, W , available from the prime mover is
i
.
W = 760 1( − 0 10)
i
˙
W = 684 .0
i
For this illustrative example, the prime mover of each of the two compressor
units derated input power is greater than the actual shaft horsepower needed, thus,
the selected compressor units can be operated at this 4,000 ft surface location
elevation (while drilling at a depth of 10,000 ft).
8.4 Prime Mover Fuel Consumption
In this section the fuel consumption of the prime mover for the compressor
system will be discussed. Illustrative examples of the fuel consumption were
discussed in detail in Chapter 4. In this section the illustrative examples in this
chapter will be completed with the calculation of the approximate fuel needed on the
drilling location for the compressor system.
Illustrative Example 8.3c describes the implementation of the basic planning
step No. 10 given in Section 8.1.
Illustrative Example 8.3c In Illustrative Example 8.3a the semi-trailer mounted
unit with the Dresser Clark CFB-4, four-stage, reciprocating piston compressor
system was selected for the drilling operation. In Illustrative Examples 8.3a and
8.3b two of these compressor units were utilized to drill the interval from 7,000 ft to
10,000 ft. Each compressor unit has a volumetric flow rate of 1,200 acfm. To
estimate the total diesel fuel needed by each compressor unit it is necessary to
estimate the fuel consumption of the compressor units’ Caterpillar Model D398,
diesel fueled, turbocharged, prime mover. The anticipated drilling rate of penetration