1. n. [Formation Evaluation]

The result of certain drilling conditions that cause the borehole to take the shape of a corkscrew. Most logging tools are much longer than the wavelength of the corkscrew, and therefore see it as a change in standoff or a change in hole size. For this reason, the corkscrew is often observed as a wave on the caliper log. A corkscrew hole affects measurements sensitive to standoff, such as induction and neutron porosity, and may affect pad tools, if they cannot follow the changes.

Synonyms: spiral borehole

See: bad hole,  cave effect