Page 46 - Air and gas Drilling Field Guide 3rd Edition

3.1 Drilling Location 37

Figure 3-1 shows the primary compressors (low pressure) that supply com-
pressed air to a flow line between the compressors and the rig standpipe. In this
example there are two primary compressors supplying the rig. These compressors
intake air from the atmosphere and compress the air in several stages of mechanical
compression. These primary compressors are positive displacement fluid flow
machines, either reciprocating piston, or rotary compressors (see Chapter 5 for
more details). These primary compressors are usually capable of an intake rate of
1200 acfm (actual cubic feet per minute) (566.3 actual liters/sec) of atmospheric
air and an output flow of compressed air at pressures up to approximately 300 psig
2
(207 N/cm gauge). These primary compressors expel their compressed air into
the flow line to the standpipe of the drilling rig. This flow line is usually an API
2 7/8-in (73 mm)(OD) line pipe (or an ASME equivalent) or larger [3]. Down-
stream along this flow line from the primary compressors is the booster compres-
sor. This booster compressor is a reciprocating piston compressor. The booster
compressor is used to increase the flow pressure from the primary compressors
2
to pressures up to approximately 1000 psig (690 N/cm gauge). In most drilling
2
operations the injection pressure is less than 300 psig (207 N/cm gauge)and,
therefore, the booster compressor is commonly used only for special drilling opera-
tions such as directional drilling with a downhole motor.
Downstream from the booster compressor are liquid pump systems that allow
water to be injected into the compressed air flow to the rig. Also, solids can
be injected into the compressed air flow. This is accomplished by injecting the
solids into a small water tank and then the water with the entrained solids is
injected into the air flow.
Along the flow line leading from the compressors to the drilling rig standpipe
is an assembly of pressure gauges, temperature gauges, valves, and a volumetric
flow rate meter [3]. This instrumentation is critical in successfully controlling
air drilling operations. Also along this flow line is a safety valve. This flow line
safety valve acts in a similar manner as the safety valves on each of the compres-
sors in releasing pressure in the event the pressure exceeds safe limits. Also on
the flow line is a valve allowing the compressed air flow to be diverted either
to the atmosphere or to primary and secondary jets in the blooey line.
The blooey line runs from the top of the annulus to the burn pit and allows the
compressed air with the entrained rock cuttings to exit the circulating system to
the atmosphere. The blooey line is about 100 to 200 ft (30.5 to 61.0 m)in length.
Usually the blooey line is an API 8 5/8-in (219 mm)(OD) casing or larger [4].
However, some blooey line systems are fabricated with two smaller diameter
parallel lines. As shown in Figure 3-1, the exit (to the atmosphere) of the blooey
line expels the air with the rock cuttings into a burn pit. For oil and natural gas dril-
ling operations, a pilot flame is placed at the exit of the blooey line. This ignites any
hydrocarbons produced exiting the blooey line with the circulating air.
Figure 3-1 shows how the drilling location is oriented so that the blooey line
exit is downwind of the prevailing wind over the site. This keeps dust or smoke
from blowing across the location.