RAT HOLE

1. A slanting hole about 25 feet deep into which the grief stem is lowered to lubricate or adjust the swivel or to add a joint of drill pipe to the drilling string. 2. A borehole reduced in size by coring. Synonym = Kelly hole. 3. To prepare for rotary drilling by drilling with a small bit and leaving a seat for the casing. 4. To reduce the size of the borehole and feel ahead.

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