PROCESS OF ELECTRIC LOGGING OF CASED WELL Russian patent published in 2004 - IPC

FIELD: geophysical investigation of wells, measurement of electric resistance of formation of rocks surrounding well cased by metal column. SUBSTANCE: according to invention there is used sonde comprising three equidistant measurement electrodes and two measurement electrodes located outside limits of zone and current electrodes positioned in symmetry relative to center measurement electrode. Electric current in the form of alternating rectangular pulses is fed into column through first (upper) current electrode. Current from output of self-balancing potentiometer which automatically keeps potential difference equal to zero between extreme measurement electrodes into second (lower) current electrode. Potential of electric field of column in point of contact of center measurement electrode with it and second potential difference of section of column between extreme measurement electrodes are measured in time intervals of galvanic excitation in each period of current on termination of induction transit process. Specific electric resistance is established by corresponding formula. EFFECT: exclusion of inductions distorting measurement results. 2 cl, 4 dwg