Logging system for earth formations

Claim 1

IN APPARATUS FOR LOGGING EARTH FORMATIONS TRAVERSED BY A BOREHOLE, THE COMBINATION COMPRISING: MEANS FOR ELECTRICALLY ENERGIZING EARTH FORMATIONS INCLUDING A SOURCE OF ALTERNATING CURRENT; A SUBSURFACE UNIT CONTAINING EQUIPMENT FOR LOGGING A BOREHOLE; MEANS TO SUPPORT AND VERTICALLY MOVE SAID UNIT WITHIN A BOREHOLE DURING A LOGGING OPERATION THEREIN INCLUDING A CABLE ATTACHED TO SAID UNIT, SAID CABLE HAVING AT LEAST THREE ELECTRICAL CONDUCTORS; MEANS FOR CONNECTING SAID ALTERNATING CURRENT SOURCE TO ONE OF SAID CONDUCTORS; MEANS TO MEASURE AND RECORD THE NATURAL POTENTIAL OF EARTH FORMATIONS; MEANS TO MEASURE AND RECORD THE RESISTIVITY OF EARTH FORMATIONS INCLUDING AT LEAST ONE POTENTIAL ELECTRODE, AN AMPLIFIER, AND A RECTIFIER CARRIED BY SAID UNIT; MEANS TO MEASURE AND RECORD THE CONDUCTIVITY OF EARTH FORMATIONS INCLUDING A TRANSMITTER COIL CARRIED ON SAID UNIT, A HIGH FREQUENCY OSCILLATOR FOR SUPPLYING CURRENT TO SAID TRANSMITTER COIL MOUNTED ON SAID UNIT BELOW SAID TRANSMITTER COIL WHEN SAID UNIT IS DISPOSED IN LOGGING POSITION, MEANS TO ENERGIZE SAID OSCILLATOR FROM SAID CURRENT SOURCE, LEAD WIRES CARRYING CURRENT BETWEEN SAID OSCILLATOR AND SAID TRANSMITTER COIL EXTENDING DOWNWARDLY FROM SAID TRANSMITTER COIL TO SAID OSCILLATOR, AND A RECEIVER COIL CARRIED ON SAID UNIT LONGITUDINALLY SPACED APART FROM AND ABOVE SAID TRANSMITTER COIL WHEN SAID UNIT IS DISPOSED IN LOGGING POSITION IN A BOREHOLE, THE DISPOSITION OF SAID OSCILLATOR BELOW SAID TRANSMITTER COIL AND SAID TRANSMITTER COIL BETWEEN SAID OSCILLATOR AND SAID RECEIVER COIL, ENABLING THE LEAD WIRES FROM SAID OSCILLATOR TO REACH SAID TRANSMITTER COIL WITHOUT CLOSELY APPROACHING SAID RECEIVER COIL, WHEREBY STRAY PICKUP BY SAID RECEIVER COIL OF UNWANTED SIGNALS FROM SAID LEAD WIRES IS SUBSTANTIALLY ELIMINATED;