Magnetic Susceptibility (MS) is the degree of magnetization of any material under external magnetic field.
When examining the common matrix minerals associated with hydrocarbon reservoirs the following key factors can be determined:
Diamagnetic: low, negative magnetic susceptibility minerals such as quartz and calcite fall into this category.
Paramagnetic: positive magnetic susceptibility, with significantly higher magnitudes than the diamagnetic minerals.
Permeability: controlling clays such as illite and chlorite fall into this category.
Since clean sands are characterised by net negative values of magnetic susceptibility, and muddy sands and shales are typified by net positive values of magnetic susceptibility, the negative or positive sign of the magnetic susceptibility can give a first pass indication of the broad permeability zonations.
In general terms, high permeability is expected in the clean sands (except in low permeability naturally cemented regions), and lower permeability in the muddy sands and shales (where there are increased amounts of permeability-controlling clay).
Key reading: D.K. Potter; “Magnetic Susceptibility as a Rapid, Nondestructive Technique for Improved Petrophysical Parameter Prediction” Petrophysics, Vol. 48, No. 3 (June 2007); pp. 191–201;
Although the negative or positive sign of the magnetic susceptibility can give a first pass indication of the broad permeability zonations our MagPI® technique takes this relationship to another level.
When working on cuttings we can take a number of steps which identify contaminants and remove their effect on the readings, and arrive at a corrected reading. This allows us to calculate an estimation which has been found, in blind tests, to correlate remarkably well against measured permeability using other methods.
The process is inexpensive, rapid, non-destructive, non-nuclear and environmentally friendly.