A technique for measuring the effect of pits and holes in the inner wall of a casing on a high-frequency electrical signal induced in the casing. The eddy-current measurement is used in conjunction with a flux-leakage measurement to determine casing corrosion, the latter being sensitive to the defects on both the inner and outer walls.The principle of measurement is similar to the openholeinduction log, but at higher frequencies. A transmitter coil produces a magnetic field that induces eddy currents in the casing wall. These currents generate their own magnetic field that induces a signal in two closely spaced receiver coils. In smooth casing, these signals are the same, but if the inner wall is pitted, the signals are different. Transmitter-receiver combinations are placed on multiple pads applied against the casing at several azimuths to fully cover the casing wall.

Related Terms:

casing-inspection log
flux leakage