1. n. [Well Testing]

The value of wellbore radius that produces equivalent results to those obtained using a skin factor of zero. It is possible to represent departures from ideal (zero skin) behavior by using the skin effect, or alternatively by changing the value of the effective wellbore radius. For a positive skin effect, effective wellbore radius is smaller than actual wellbore radius. For a negative skin effect, such as often obtained after well stimulation, effective wellbore radius is larger than actual well radius.

See: skin effect,  skin factor