Page 466 - Air and Gas Drilling Manual

9-70 Air and Gas Drilling Manual
Figure 9-7 shows that the maximum air volumetric flow rate injected into the
drill string is 1,168 acfm (at a drilling depth of 10,000 ft) and from Figure 9-6 the
maximum air injection pressure into the drill string is 420 psia (at a drilling depth
of 7,000 ft). This data allows for the selection of the primary compressor unit to be
used in the drilling operation. The primary compressor unit for an aerated drilling
operation must be used in a different manner than its use in an air drilling operation.
As can be seen in Figures 9-6 and 9-7, the aerated drilling operation requires varying
the air volumetric flow rate as the drilling progresses. Since primary compressors
output a constant volumetric flow rate, it is necessary to measure with a flow meter
the volumetric flow rate flowing to the top of the drill string and vent the remainder
of the compressor output to the atmosphere.

Figure 9-6: Drill string injection pressure as a function of drilling time (drilling depth)
for Illustrative Example 9.3.

There are several possible candidate compressor units given in Section 4.7 of
Chapter 4 that could be used to provide the compressed air for this example drilling