Page 555 - Air and Gas Drilling Manual

10-80 Air and Gas Drilling Manual
For this illustrative example, the derated input power of the prime mover that
operates the compressor is greater than the actual shaft horsepower needed by the
compressor, thus, the selected compressor unit can be operated at this 4,000 ft
surface location elevation (while drilling at a depth of 7,000 ft).
The volumetric flow rate of gas to create a stable foam drilling fluid is very
dependent upon the flow resistance in the circulation system. This resistance is the
sum of the major and minor flow friction losses in the flow system. This friction
resistance creates choking of the circulation system and, therefore, generally increases
the average pressure and in turn increases the average specific weight of the foam
drilling fluid in the annulus and elsewhere in the circulation system. This can be
seen by comparing the results from Illustrative Example 10.1 (non-friction) to those
obtained from Illuatrative Example 10.2 (friction).
In general, foam drilling operations use a back pressure valve at or near the exit
of the annulus. Thus, the main choking in the circulation system is the major and
minor friction losses inside the drill string and in the annulus. However, by
comparing the differences in the non-friction and friction results in Illustrative
Examples 10.1 and 10.2 to the differences in the non-friction and friction results in
Illustrative Examples 9.2 and 9.3 it can be seen that the differences are greater in the
aerated drilling fluid examples. These larger differences are due to the fact that the
aerated drilling fluid examples have used the natural flow resistance of the surface
return flow line (which can be significant). The foam drilling fluid models have
used a constant back pressure and, thus, the flow resistance of the surface return flow
line has no effect on the calculations.
10.5 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 example in this
chapter will be completed with the calculation of the approximate fuel needed on the
drilling location for the compressor system.
Illustrative Example 10.3 describes the implementation of the basic planning
step No. 10 given in Section 10.1.
Illustrative Example 10.3 In Illustrative Example 10.2 the semi-trailer
mounted unit with the Ingersoll Rand Model HHE, three-stage, reciprocating piston
compressor system was selected for the drilling operation. In Illustrative Examples
10.2 the compressor unit was utilized to drill the interval from 7,000 ft to 10,000 ft.
The compressor unit has a volumetric flow rate of 1,500 acfm. The compressed air
flowing to the drilling operation varies over the drilled interval from 1,240 acfm to
1,658 acfm. But the compressor must output 1,500 acfm. The volumetric flow rate
to the borehole must be varied as the interval is drilled and the excess is vented to
the atmosphere. Therefore, to estimate the total diesel fuel needed by the compressor
unit it is necessary to estimate the fuel consumption of the compressor units’
Caterpillar Model 3508, diesel fueled, turbocharged, prime mover. The anticipated
drilling rate of penetration is estimated to be 60 ft/hr. The vertical interval section
to be drilled is from a depth of 7,000 ft to depth of 10,000 ft, or a 3,000 ft length of