Page 246 - Air and Gas Drilling Manual

5-88 Air and Gas Drilling Manual
˙
.8
W = 340
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 taken into account.
5.3.3 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 will be
completed with the calculation of the approximate fuel needed on the drilling
location for the operation of the compressor system.
Illustrative Examples 5.5c, and 5.6c describe the implementation of the basic
planning step No. 10 given in Section 5.1 (planning step No. 11 is discussed in
Chapter 8).
Illustrative Example 5.5c Determine the total diesel fuel needed by the semi-
trailer mounted stand alone Dresser Clark Model CFB-4, four-stage reciprocating
piston primary compressor unit (see Figure 4-25) used in Illustrative Example 5.5b.
This compressor unit has a volumetric flow rate of 1,200 acfm. To estimate the
total diesel fuel needed by this 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 is estimated
to be 30 ft/hr. Since the vertical depth to be drilled is 2,400 ft, then the estimated
actual drilling time to reach this depth is approximately 80 hours.
In Illustrative Example 5.5b the injection pressure into the top the annulus when
drilling at 2,400 ft of depth was found to be 34.9 psia. Using similar calculations
the injection pressures for lesser depths can be found. Figure 5-19 shows these
injection pressures as a function of drilling time (or drilling depth).
The reciprocating piston compressor is not a fixed pressure ratio machine like
the rotary screw compressor. As long as there is sufficient power available from the
prime mover the reciprocation piston compressor will match the back pressure
resistance. Thus, Figure 5-19 shows only one curve indicating the injection pressure
is the same as the pressure output of the compressor.
In Illustrative Example 5.5b it was found that the actual shaft horsepower
required by this reciprocating piston compressor to compress air to 34.9 psia was
81.2 (at 2,400 ft of depth). Also in Illustrative Example 5.5b the derated
horsepower available from the Caterpillar Model D398 was found to be 722.0.
Drilling at a depth of 2,400 ft, the prime mover power ratio is