ELECTROMAGNETIC ISOPARAMETRIC LOGGING METHOD Russian patent published in 2009 - IPC G01V3/28 

FIELD: electrical engineering.

SUBSTANCE: invention relates to geophysical investigation of electrical properties of rocks and can be used for determining electrical properties of rocks around a well, drilled for oil and gas. Probing is done using a set of N double-coil probes of different length, consisting of one exciter and one measuring coil. Exciter coils of the probes are powered by current with different harmonic frequencies at equal values of the product of the square of the length of the probe and frequency. Using each pair of adjacent probes, phase pairs of non-synchronous fluctuations of EMF of harmonic frequencies are measured. From these values, the normalised phase difference for each pair of adjacent probes is calculated by multiplying the subtracted phase by the frequency ratio greater than one, and/or by multiplying the smaller phase by frequency ratio less than one. Electrical conductivity with large and/or small resolution is determined from the normalised phase differences.

EFFECT: increased sensitivity, resolution and radial transmission distance.

3 cl, 2 dwg