Page 387 - Air and Gas Drilling Manual

8-70 Air and Gas Drilling Manual
injection pressures of as little as 5 to 10 psi. This type of warning requires intense
attention of drilling operations supervisors. Pressure recorders with rapid pressure
rate increase alarms can be installed for use by drilling supervisors. Such pressure
alarms will only be useful for operations using drill bits with open orifices (subsonic
flow in the throat of the orifices).

Figure 8-16: Ignition mixture by volume of natural gas and atmospheric air [19].
As the drill bit of a vertical dry air drilling operation approaches a hydrocarbon
bearing rock formation, the following steps should be taken to prevent hydrocarbon
downhole ignition [19, 20]:
1. Drilling should be immediately stopped.
2. Air injection should be shut off and the gas flare monitored. If the flare
is sustained, the operator should note the wetness of the cuttings at the
sample catcher (indicating whether the gas is wet; black smoke and/or
yellow color of burning gas (indicating distillate in gas); sparks at the
end of the blooey line (indicating drill cuttings are damp from distillate).
If the gas flare will not sustain or burn when the air is turned off, air
should be turned back on.