Page 633 - Air and Gas Drilling Manual

Chapter 11: Specialized Drilling Equipment 11-71
˙
760
W
(1
. 0 10
)
i
˙
W
.0
684
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).
Compressor Unit Fuel Consumption
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.
It was found above that the actual shaft horsepower required by each of the two
reciprocating piston compressor units to compress air to 356.5 psia was
approximately 304.5 (while drilling at 10,000 ft of depth). Also above it was found
that the derated horsepower available from the Caterpillar Model D398 prime mover
at the surface elevation of 4,000 ft was 684.0. Drilling at a depth of 10,000 ft, the
prime mover power ratio is
304 5 .
PR ( 100) 44 5 .
684 0 .
Using Figure 4-17 the diesel fuel consumption rate for a power level of 44.5 percent
is 0.670 lb/hp-hr of diesel fuel. The total weight rate of diesel fuel consumption per
hour is
˙ w . 0 670 (304 5 204 .0 lb/hr
. )
f
The diesel fuel consumption rate (in United States gallons) for the drilling depth of
10,000 ft is
204 0 .
q f 30 0 . gal/hr
0 8156 8 33)
(. )( .
Since there are two compressor units providing compressed air to this example
air hammer drilling operation, the total diesel fuel consumption rate while drilling at
the 10,000 ft of depth is approximately 60 gal/hr.
11.2.4 Downhole Pneumatic Sliding Vane Motors
In the late 1950s Reed Tool Company developed and field tested the first
downhole air motor [6]. This downhole air motor was a two stage sliding vane
design (a positive displacement motor design) with a two stage planetary gear
reduction gear box with a reduction ratio of 32 to 1. The field testing of the motor
revealed that the sliding vane cavities where prone to filling up with pipe scale and
other foreign particles in the compressed air flow. Also, the non-metal sliding vanes