Why use it?

Magnetic susceptibility is used to ascertain how easily a formation can be magnetised.

Alteration and oxidation zones for iron and pyrrhotite are the most common targets.

The Magnetic Susceptibility and the combined conductivity sonde {EM51} are both bottom end sonde's, however they can be ran in conjunction with up to 4 other modular units. {ie Ngam, verticality, temperature, water level, etc.}

Principle Of Operation

This sonde measures formation electrical conductivity {chargeability} and formation magnetic susceptibility {ability t be magnetised } using electromagnetic induction. The sonde includes a set of two coils for conductivity measurement and another set of two coils for magnetic susceptibility measurement.

The sonde is most effective in higher conductivity formations and low conductivity borehole fluid, including air. It is also useful in boreholes with plastic casing. Formation conductivity is typically measured in mS/m (or mmho).

Instrumentation used is produced by Geovista and operates with a digital data output.


A set of two calibration loops are supplied for the Induction. These can be used for sonde calibration and for sonde testing. The equivalent conductivity of the loops are 200 and 500mS/m.

A set of two calibration values are supplied for the Magnetic Susceptibility. The equivalent susceptibilities are 1.7 x 10-3 and 5 x 10-3 SI unit.

Sonde General Specifications

Sonde length 1.90 m Sonde diameter

45 mm Sonde weight 5.0 Kg

Induction Inter-coil spacing: 50 cm

Operating frequency: 100 kHz Measuring range: 1 to 3000 mS/m ( 0.33 to 1000 Ωm) Accuracy: 3% for range 100 to 1000 mS/m 10% for range 1000 to 3000 mS/m Mag. Susc.

Inter-coil spacing: 25 cm Operating frequency: 2 kHz Measuring range: 10-4 to 2 SI unit Accuracy: 3%