Induction logging system utilizing surface reciprocal producing means

Claim 1

A SYSTEM FOR INVESTIGATING THE LITHOLOGY OF FORMATIONS SURROUNDING A BORE HOLE COMPRISING, IN COMBINATION, SURFACE EQUIPMENT; A LOGGING TOOL; A CABLE INCLUDING A PLURALITY OF CONDUCTORS CONNECTING SAID SURFACE EQUIPMENT TO SAID LOGGING TOOL; MEANS INCLUDING SAID CABLE OPERABLE TO CAUSE SAID LOGGING TOOL TO TRAVERSE THE EXTENT OF THE BORE HOLE; A COIL SYSTEM FORMING A PART OF SAID LOGGING TOOL AND INCLUDING AT LEAST ONE TRANSMITTING COIL AND AT LEAST TWO RECEIVING COILS DISPOSED ADJACENT SAID TRANSMITTING COIL IN FIXED RELATION THERETO; A SOURCE OF ALTERNATING POWER; MEANS INCLUDING SAID SOURCE, CERTAIN ONES OF SAID PLURALITY OF CONDUCTORS AND SAID TRANSMITTER COIL TO ESTABLISH AN ELECTROMAGNETIC FIELD OF PRESELECTED FREQUENCY IN THE FORMATION ADJACENT SAID COIL SYSTEM; DETECTING MEANS INCLUDING AT LEAST A PAIR OF SAID RECEIVER COILS TO DETECT THE SECONDARY FIELD ESTABLISHED BY THE FORMATIONS AND SAID ELECTROMAGNETIC FIELD BY PRODUCING SIGNALS SYSTEMATICALLY RELATED THERETO, MEANS TO EFFECTIVELY ELIMINATE VOLTAGES MUTUALLY INDUCED IN SAID RECEIVER COILS; MEANS INCLUDING FEWER RECEIVER COILS THAN SAID DETECTING MEANS TO PROVIDE A REFERENCE SIGNAL; MEANS RESPONSIVE TO SAID SIGNALS TO SEPARATE OUT OF SAID DETECTED SIGNALS THE COMPONENT IN-PHASE WITH THE TRANSMITTING COIL CURRENT; MEANS INCLUDING SELECTED ONES OF SAID PLURALITY OF CONDUCTORS FOR TRANSMITTING SAID IN-PHASE SIGNAL TO SAID SURFACE EQUIPMENT; AND SERVO RECORDING MEANS FORMING PART OF SAID SURFACE EQUIPMENT AND INCLUDING A SERVO DRIVEN SHAFT CONTROLLED BY DIFFERENCES BETWEEN SAID INPHASE SIGNAL AND A GENERATED REFERENCE SIGNAL TO CAUSE SAID SHAFT TO ROTATE TO TRANSLATE SAID IN-PHASE SIGNAL INTO AN EQUIVALENT ROTATION OF SAID SHAFT, EACH MAGNITUDE OF SAID GENERATED REFERENCE SIGNAL REPRESENTING THE ROTATIVE POSITION OF SAID SHAFT, AND MEANS COOPERATING WITH POTENTIOMETERS DRIVEN BY SAID SHAFT TO RECORD THE CONDUCTIVITY AND ITS RECIPROCAL RESISTIVITY OF THE SUBSURFACE FORMATIONS ADJACENT ANY GIVEN POSITION OF SAID COIL SYSTEM.

Claim 2

A SYSTEM FOR INVESTIGATING THE LITHOLOGY OF FORMATIONS SURROUNDING A BORE HOLE COMPRISING, IN COMBINATION, SURFACE EQUIPMENT; A LOGGING TOOL; A CABLE INCLUDING A PLURALITY OF CONDUCTORS CONNECTING SAID SURFACE EQUIPMENT TO SAID LOGGING TOOL; MEANS INCLUDING SAID CABLE OPERABLE TO CAUSE SAID LOGGING TOOL TO TRAVERSE THE EXTENT OF THE BORE HOLE; A COIL SYSTEM FORMING A PART OF SAID LOGGING TOOL AND INCLUDING AT LEAST ONE TRANSMITTING COIL AND AT LEAST TWO RECEIVING COILS DISPOSED ADJACENT SAID TRANSMITTING COIL IN FIXED RELATION THERETO; A SOURCE OF ALTERNATING POWER; MEANS INCLUDING SAID SOURCE, CERTAIN ONES OF SAID PLURALITY OF CONDUCTORS AND SAID TRANSMITTER COIL TO ESTABLISH AN ELECTROMAGNETIC FIELD OF PRESELECTED FREQUENCY IN THE FORMATION ADJACENT SAID COIL SYSTEM; DETECTING MEANS INCLUDING AT LEAST A PAIR OF SAID RECEIVER COILS TO DETECT THE SECONDARY FIELD ESTABLISHED BY THE FORMATIONS AND SAID ELECTROMAGNETIC FIELD BY PRODUCING SIGNALS SYSTEMATICALLY RELATED THERETO, MEANS TO EFFECTIVELY ELIMINATE VOLTAGES MUTUALLY INDUCED IN SAID RECEIVER COILS; MEANS INCLUDING FEWER RECEIVER COILS THAN SAID DETECTING MEANS TO PROVIDE A REFERENCE SIGNAL; MEANS RESPONSIVE TO SAID SIGNALS TO SEPARATE OUT OF SAID DETECTED SIGNALS THE COMPONENT IN-PHASE WITH THE TRANSMITTING COIL CURRENT; MEANS INCLUDING SELECTED ONES OF SAID PLURALITY OF CONDUCTORS FOR TRANSMITTING SAID IN-PHASE SIGNAL TO SAID SURFACE EQUIPMENT; AND SERVO RECORDING MEANS FORMING PART OF SAID SURFACE EQUIPMENT AND INCLUDING A SERVO DRIVEN SHAFT CONTROLLED BY DIFFERENCES BETWEEN SAID INPHASE SIGNAL AND A GENERATED REFERENCE SIGNAL TO CAUSE SAID SHAFT TO ROTATE TO TRANSLATE SAID IN-PHASE SIGNAL INTO AN EQUIVALENT ROTATION OF SAID SHAFT, EACH MAGNITUDE OF SAID GENERATED REFERENCE SIGNAL REPRESENTING THE ROTATIVE POSITION OF SAID SHAFT, AND MEANS COOPERATING WITH POTENTIOMETERS DRIVEN BY SAID SHAFT TO RECORD THE CONDUCTIVITY AND ITS RECIPROCAL RESISTIVITY OF THE SUBSURFACE FORMATIONS ADJACENT ANY GIVEN POSITION OF SAID COIL SYSTEM.