Page 209 - Air and Gas Drilling Manual

Chapter 5: Shallow Well Drilling Applications 5-51
The approximate total diesel fuel needed to drill the borehole is given by the
integration of the area under the curve in Figure 5-11. This is approximately 728
gallons. It is standard practice to assume a 20 percent additional volume of fuel for
blowing the hole between connections and other operations on the drill rig.
Therefore, the approximate total diesel fuel needed at the drilling location is 873
gallons. For this example, this diesel fuel amount is for the drilling rig prime
mover that operates both the integrated rotary screw compressor and the hydraulic
pump that operates the rotary top drive system.
b) Gardner Denver Model WEN Reciprocating Piston Primary Unit
In Illustrative Example 5.2b an alternate combination for drilling this shallow
well is the trailer mounted rotary drilling rig (see Figure 1-4) with the stand alone
Gardner Denver Model WEN reciprocating piston primary compressor unit (see
Figure 4-22). This compressor unit has a volumetric flow rate of 700 acfm. To
estimate the total diesel fuel needed by this compressor unit it is necessary to
estimate the fuel consumption of the compressor unit’s Caterpillar Model D353,
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 1,200 ft, then the
estimated actual drilling time to reach this depth is approximately 40 hours.
In Illustrative Example 5.2b the injection pressure into the top of the drill string
when drilling at 1,200 ft of depth was found to be 80.7 psia. Using similar
calculations the injection pressures for lesser depths can be found. Figure 5-12
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 5-12 shows only one curve indicating the injection pressure
is the same as the pressure output of the compressor.
In Illustrative Example 5.2b it was found that the actual shaft horsepower
required by this reciprocating piston compressor to compress air to 80.7 psia was
98.0 (at 1,200 ft of depth). Also in Illustrative Example 5.2b the derated
horsepower available from the Caterpillar Model D353 was found to be 230.0. At a
depth of 1,200 ft, the prime mover power ratio is
PR = 98 0 . ( 100) = 42 6 .
230 0 .
From Figure 4-17 the approximate diesel fuel consumption rate at this power level is
approximately 0.690 lb/hp-hr. The total weight rate of diesel fuel consumption per
hour is
˙ w = . 0 690 (98 . ) =0 67 .5 lb/hr
f
The diesel fuel consumption rate (in United States gallons) for the drilling depth of
1,200 ft is