1. n. [Formation Evaluation]
The ability of the formation to resist electrical conduction, as derived from the change in position of the peaks of an electromagnetic wave generated in a propagation resistivity measurement. At the frequencies used, the phase shift depends mainly on the resistivity of the material with a small dependence on dielectric permittivity, particularly at high resistivity. Common practice is to transform the phase shift to resistivity assuming that the dielectric permittivity is related to resistivity by a simple algorithm. The transform also depends on transmitter/receiver spacings and tool design. For a 2-MHz measurement, a typical measurement range is 0.2 to 200 ohm-m. Above 200 ohm-m, the dielectric effects become too variable and it is preferable to use the dielectric resistivity.