Page 552 - Air and Gas Drilling Manual

Chapter 10: Stable Foam drilling 10-77
(i.e., 1,860 ft of drilling interval or a depth of 8,860 ft, see Figure 10-6). The
primary compressor unit also has sufficient injection pressure capability to provide
the injection pressure required by the foam drilling operation (see Figure 10-4).
When the air volumetric flow rate requirement exceeds 1,500 acfm, a second primary
compressor must be placed on line to provide the additional air to the foam
operation.

Figure 10-6: Drill string air injection volumetric flow rate as a function of drilling time
(drilling depth) for Illustrative Example 10.2.
The last criteria is to check whether the prime mover of this primary compressor
unit has the power to operate the compressor at the 4,000 ft surface elevation. The
highest injection pressure occurs while drilling out of the casing shoe at a depth of
7,000 ft. This injection pressure is approximately 275 psia. Even though the
required air volumetric flow rate at this depth is approximately 1,240 acfm, the
compressor must output the full 1,500 acfm (the remainder is vented). The
compressor is a three stage reciprocating piston compressor. Therefore,