1. n. [Production Logging]

An in-situ measurement of the thickness of a casing or tubing string using an electromagnetic technique. The result is presented as a type of casing-inspection log, giving an estimate of metal loss and detecting corrosion. In the usual method, a coil centered inside the casing generates an alternating magnetic field. Another coil farther up the tool measures the phase shift introduced by the casing. This phase shift depends on the casing-wall thickness and internal diameter, as well as the casing conductivity and magnetic permeability. The effects change at different frequencies, so that by varying the frequency, the thickness and internal diameter can be uniquely determined. Electromagnetic thickness can also be measured using other techniques, for example from a casing-potential profile or a flux-leakage measurement.

See: casing-inspection log,  casing-potential profile,  electromagnetic caliper,  flux leakage,  magnetic permeability,  phase shift