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7 The wall cake created by circulating drilling fluid prevented
formations from collapsing.
8 The pump moves the clean mud back down the hole.
9 As you now know, one disadvantage of a rotary rig is that workers
have to worry about soft formations caving in on the bit and
sticking it.
10 Drilling mud or drilling fluid can be a liquid, a gas, or a
combination of the two.
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