METHOD FOR ELECTRIC LOGGING OF CASED WELLS Russian patent published in 2001 - IPC

FIELD: geophysical explorations of wells, applicable in determination of electrical resistance of rock strata surrounding the well cased by a metal column. SUBSTANCE: the method consists in measurement of the electric field potential and its second difference with the aid of a unipolar four-electrode probe contacting with the case column. The probe is made in the form of three equidistant measuring electrodes and three current electrodes, two current electrodes are positioned symmetrically relative to the middle measuring electrode, the third electrode is positioned in the middle at the level of the middle measuring electrode and connected to the column in the point that is incompatible with the point of contact with the column of the middle measuring electrode. Electric current is applied to each of the three current electrodes from the same source pole. The potential of the electric field of the middle measuring electrode, the first difference of potentials between the two extreme measuring electrodes, the second difference of potentials are measured at each of the three current applications. EFFECT: facilitated procedure. 3 dwg