Page 212 - Air and Gas Drilling Manual

5-54 Air and Gas Drilling Manual
footprint. In general, for a given volumetric flow rate, reciprocating piston
compressors are more bulky and have a larger surface area footprint than their rotary
compressor counterpart.
Illustrative Example 5.3c Determine the approximate total volume of diesel
fuel needed at the drilling location to operate the compressor system when using
direct circulation to drill the borehole described in Illustrative Examples 5.3a and
5.3b.
In Illustrative Example 5.3b it was planned that the semi-trailer mounted
drilling rig in Figure 1-4 was to be used to drill the 6 1/4 inch diameter, 2,400 ft
deep borehole. It was also determined in Illustrative Example 5.3b that two skid
mounted primary Gardner Denver Model WEN reciprocating piston compressor
primary units (see Figure 4-22) would be needed to air drill the borehole. These two
compressor units have a total volumetric flow rate of 1,400 acfm. To estimate the
total diesel fuel needed by these stand alone compressor units it is necessary to
estimate the fuel consumption of the compressor units’ Caterpillar Model D353,
diesel fueled, turbocharged, prime movers. The anticipated drilling rate is estimated
to be 90 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 26.7 hours.
In Illustrative Example 5.3b the injection pressure into the top of the drill string
when drilling at 2,400 ft of depth was found to be 148.3 psia. Using similar
calculations the injection pressures for lesser depths can be found. Figure 5-14
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 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 5-14 shows only one curve indicating the injection pressure is the same
as the pressure output of the two compressors.
In Illustrative Example 5.3b it was found that the actual shaft horsepower
required by each of the two reciprocating piston compressors to compress air to
148.3 psia was 144.3 (at 2,400 ft of depth). Also in Illustrative Example 5.3b the
derated horsepower available from the Caterpillar Model D353 was found to be
243.0. At a depth of 2,400 ft, the prime mover power ratio is
PR = 144 3 . ( 100) = 59 4 .
243 0 .
From Figure 4-17 the diesel fuel consumption rate at this power level is
approximately 0.573 lb/hp-hr. The total weight rate of diesel fuel consumption per
hour is
˙ w = . 0 573 (144 . ) =3 82 .7 lb/hr
f
The diesel fuel consumption rate (in United States gallons) for the drilling depth of
2,400 ft is