Page 209 - Air and gas Drilling Field Guide 3rd Edition

200 CHAPTER 8 Air, Gas, and Unstable Foam Drilling

SI Units: Number of Primary Compressors Units Required
As in Illustrative Example 8.1, the primary compressor of choice will be the four
stage reciprocating piston Dresser Clark CFB-4 (see Chapter 5, Section 5.7.2).
This compressor has a rated input of 566.3 actual liters/sec. In this improved
Illustrative Example 8.2 solution, the minimum air volumetric flow rate needed
to clean the well is 940.96 actual liters/sec. Therefore, to drill this example sec-
tion of the well at the 1219-m surface location, two Dresser Clark CFB-4 primary
compressors will be adequate, as they would give a factor of safety of greater
than 1.2. Therefore, two primary compressors must be used.
The factor of safety for this illustrative example is
2 ðÞ 566:3Þ
ð
FS ¼
ð 940:96Þ
FS ¼ 1:2036:
The two Dresser Clark CFB-4 primary compressors will inject 1132.6 actual liters/
sec into the circulation system.
The difference in the factor of safety results between Illustrative Example 8.1 and
Illustrative Example 8.2 is due to the inclusion in 8.2 of the major and minor losses
of the surface equipment (i.e., blooey line, Tee, blooey line valves) and the inclusion
of a more accurate treatment of open hole annulus absolute surface roughness.
Referring back to Chapter 5, Section 5.7, several compressor packages could
have been used.
The two stage reciprocating piston Gardner Denver Model WEN primary com-
pressor in Chapter 5, Section 5.7.1 is rated at 700 acfm (330 actual liters/sec).
Applying the factor of safety of 1.2 would require the use of four of these primary
compressors to the example drilling project. This would mean that the
volumetric flow rate of air injected into the circulation system of the well
would be 2800 acfm (1321 actual liters/sec). This would give a factor of safety
of 1.4.
The two stage helical lobe (screw) Ingersoll Rand Model XHP 1170 primary com-
pressor in Chapter 5, Section 5.7.3 is rated at 1170 acfm (552.1 actual liters/sec).
As discussed in Chapter 5, the screw compressor has a seal wear problem that
requires that the rated volumetric flow rate be reduced by approximately 7%
when these compressors are applied at a field location. This means that the dera-
ted primary compressor output is approximately 1088 acfm (513.4 actual liters/
sec). Applying the factor of safety of 1.2 would require use of three of these
primary compressors to the example drilling project. This would mean that the
volumetric flow rate of air injected into the circulation system of the well would
be 3264 acfm (1540.3 actual liters/sec). This would give a factor of safety of 1.46.
Here again the operational preference would be to use the four stage recipro-
cating piston Dresser Clark CFB-4 primary compressor package with a factor of
safety of 1.64.