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tight hole


1. n. [Drilling]
A section of a wellbore, usually openhole, where larger diameter components of the drillstring, such as drillpipe tool joints, drill collars, stabilizers, and the bit, may experience resistance when the driller attempts to pull them through these sections.
See: openhole, tool joint
2. n. [Drilling]
A well that the operator requires be kept as secret as possible, especially the geologic information. Exploration wells, especially rank wildcats, are often designated as tight. Unfortunately, this designation is of questionable benefit in keeping the data secret.

Taken from;

Schlumberger

http://www.glossary.oilfield.slb.com/en/Terms/t/tight_hole.aspx