Page 47 - Air and gas Drilling Field Guide 3rd Edition

38 CHAPTER 3 Surface Equipment

3.2 FLOW LINE TO THE RIG
The flow line to the standpipe of the drilling rig acts as a manifold collecting
the compressed air outputs from the primaries. These flow lines are API 2 7/8-in
(73 mm)(OD) or 3 1/2 (89 mm)(OD) steel line pipe (or ASME equivalent)[5].
The valves in the flow line at the booster compressor allow the air flow from
the primaries to be diverted to the booster when high compression of the air
is needed. When higher compression is not needed, the booster compressor
is isolated with the check valves in the flow line to the rig.

3.2.1 Bleed-Off Line
The bleed-off line allows pressure to be released throughout the flow line to the
rig and inside the standpipe, rotary hose, kelly, and the drill pipe to the depth of
the first float valve (see Figure 3-1). The bleed-off line is usually run to the blooey
line and exits into that line. The bleed-off line is generally used when drill pipe
connections are made, replacing the drill bit (making round trips), and for other
operations where the well is opened to the atmosphere.

3.2.2 Scrubber
The scrubber removes excess water in the compressed air flow in the flow line. If the
humidity of the atmospheric air is high, then as the air is compressed in the compres-
sors much of the water will return to the liquid state. Dry air drilling operations
require the removal of this water before the compressed air is injected into the well.
The scrubber is incorporated into a surge tank. The water in the compressed air flow
is collected in the bottom of the surge tank as the air flows through this tank and is
vented from time to time to eliminate the water from the line.

3.2.3 Water Injection Pump
Unstable foam (mist) drilling operations require the injection of water into the
compressed air flow before the air is injected into the well. The water injection
pump injects water, chemical corrosion inhibitors, and liquid foamers into the
compressed air flow line. Figure 3-2 shows a skid-mounted water injection pump
for air and gas drilling operations. These skid-mounted water injection pumps are
used for deep drilling operations. These pumps are capable of injecting up to
20 bbl/hr (75.7 liters/hr) into the air or gas flow to the well.
The smaller drilling rigs have onboard water injection pumps. These smaller
rig water injection pumps have capabilities from 10 to 25 gal/min (37.9 to 94.6
liters/min). The small water injection pump carries out the same objective on
these smaller rigs as the skid-mounted water pump for the larger double and tri-
ple drilling rigs. The injection of water and appropriate chemicals and foamer is
a vital option for air and gas drilling operations. Very few air and gas drilling