METHOD FOR ELECTRICAL LOGGING CASED WELLS Russian patent published in 2010 - IPC G01V3/20 

FIELD: physics; geophysics.

SUBSTANCE: invention relates to geophysical exploration of wells and is meant for determining electrical resistivity of rocks in cased wells. A penta-electrode probe is used, which is made in form of three measuring electrodes and two current electrodes placed in series and equidistant along the axis of the well. Dipolar rectangular direct current pulses are applied to the current electrodes. During each application, electric field potential of the middle measuring electrode is measured, as well as the first potential difference between outermost measuring electrodes and the first electric potential difference between one of the outermost electrodes and the central electrode. The electric potential and its first differences are digitised not earlier by 0.4 s after polarity reversal of current with sampling rate equal to or greater than 5 Hz. All digitised signal quanta are processed, filtered and then used to determine electrical resistivity of rock formation surrounding the cased well.

EFFECT: wider dynamic range for determining true electrical resistivity with error of 5%.

2 cl, 2 dwg