Page 556 - Air and Gas Drilling Manual

Chapter 10: Stable Foam drilling 10-81
borehole. Therefore, the estimated actual drilling time to drill this interval is
approximately 50 hours.
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 reciprocating piston compressor will match the back pressure resistance.
Thus, Figure 10-4 shows only one curve indicating the injection pressure is the same
as the pressure output of the compressor unit.
In Illustrative Example 10.2 it was found that the actual shaft horsepower
required by the reciprocating piston compressor unit to compress air to 275 psia was
approximately 367.3 (at 7,000 ft of depth). Also in Illustrative Example 10.2 the
derated horsepower available from the Caterpillar Model 3508 prime mover at the
surface elevation of 4,000 ft was found to be 579.6. Drilling at a depth of 7,000 ft,
the prime mover power ratio percent is
367 3 .
PR ( 100) 63 4 .
579 6 .
Entering the abscissa of Figure 4-17 with the power ration percent, the approximate
fuel consumption rate can be read on the ordinate using the diesel fuel curve. The
approximate fuel consumption rate at this power level is 0.552 lb/hp-hr. The total
weight of diesel fuel consumption per hour is
. )
˙ w . 0 552 (367 3 202 .8 lb/hr
f
The diesel fuel consumption rate (in United States gallons) for the drilling depth of
7,000 ft is

202 8 .
q 29 8 . gal/hr
f
0 8156 8 33)
(. )( .
Using the data in Figure 10-4 and similar calculations as those given above, the
diesel fuel consumption rate as a function of drilling time (or drilling depth) can be
obtained. Figure 10-8 shows the diesel fuel consumption rate as a function of
drilling time (or drilling depth) for the reciprocating piston compressor unit. The
approximate total diesel fuel needed for the compressor unit is obtained by the
integration of the area under the curve in Figure 10-8. One compressor unit is used
throughout the 50 hours of drilling. The fuel needed for this compressor is
approximately 1,500 gallons. It is standard practice to assume a 20 percent
addtional volume of fuel for circulating the well and other compressor operations on
the rig. Therefore, the total diesel fuel consumption for this first compressor is
about 1,800 gallons. The second compressor is place on line at 31 hours into the
operation. The fuel needed for this compressor is 600 gallons. Adding the standard
20 percent gives a total diesel fuel consumption for this second compressor of about
720 gallons. Therefore, the total diesel fuel needed for the two compressor units is
approximately 2,520 gallons.