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152 Part II Gas Drilling Systems

Figure 7.2 Drill cuttings above the shoulder of drill collars.

borehole washout limitations, mud rings can be cut by adding detergent
to the gas. This helps solve the problem by (1) lifting the cuttings away
from the area of the collar shoulder with foam and (2) softening the
mud rings with surfactants that are less restrictive to the movements of
the drill string.
The quantity of the foaming agent should start at 1 or 2% or about
1 or 2 quarts per bbl and then be increased according to need. Enough
misting agent must be added to see just a trace of foam at the blooey
line. A good starting point is 8 bbl/hour of water. Fine or dissolved
cuttings, oil, salts, and water hardness will all affect misting agents
to some degree. A pilot test in a quart of injection water should be
performed to give an indication of where to start the mist mixture.
Tight hole problems appear to be related to mud ring problems or
floating beds. It is important to not turn off the gas and to keep working
the pipe. If the pipe is pulled up too hard, it may stick tight. Keeping
the gas circulating is essential to preventing the growth of mud rings and
reducing pipe sticking.