Page 368 - Air and Gas Drilling Manual

Chapter 8: Air, Gas, and Unstable Foam Drilling 8-51
is estimated to be 60 ft/hr. The vertical interval section to be drilled is from a depth
of 7,000 ft to a depth of 10,000 ft, or a 3,000 ft length of borehole. Therefore, the
estimated actual drilling time to drill this interval is approximately 50 hours.
In Illustrative Example 8.3b the injection pressure into the top of the drill string
when drilling at 10,000 ft of depth was found to be approximately 212.4 psia.
Using similar calculations, the injection pressures for depths from 7,000 ft to 10,000
ft can be obtained. Figure 8-8 shows these injection pressures as a function of
drilling time (or drilling depth).

Figure 8-8: Drill string injection pressure (same as compressor output pressure) for
Illustrative Example 8.3c.
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.