Nuclear magnetism well logging method and apparatus

Claim 1

APPARATUS FOR INCREASING THE SPEED WITH WHICH NUCLEAR MAGNETIC SIGNALS CAN BE GENERATED AND DETECTED IN AN EARTH FORMATION PENETRATED BY A WELL BORE AND TRAVERSED BY A LOGGING SONDE BY ALIGNING PROTONS OF SAID FORMATION IN A FIRST DIRECTION BY MEANS OF A POLARIZING FIELD, INTERRUPTING SAID POLARIZING FIELD AND, AS SAID PROTONS PRECESS ABOUT THE EARTH''S MAGNETIC FIELD, DETECTING SAID RELAXING PROTONS COMPRISING MEANS FOR TRAVERSING SAID SONDE THROUGH SAID BOREHOLE AT A VELOCITY (V), SAID SONDE INCLUDING AT LEAST A PAIR OF COILS HAVING MAGNETIC AXES, ONE OF SAID COILS HAVING AT LEAST AN EFFECTIVE PORTION OF ITS WINDINGS EXTENDING ALONG SAID WELL BORE SUBSTANTIALLY FARTHER THAN A SECOND OF SAID COILS, SAID EXTENSION ALONG SAID WELL BORE AXIS BEING IN THE DIRECTION IN WHICH SAID SONDE IS MOVED DURING THE LOGGING OPERATION AND HAVING A MAGNITUDE RELATED TO THE VELOCITY (V) OF THE SONDE AND THE POLARIZING TIME (T0) OF SAID EARTH FORMATION, A POLARIZING CURRENT SOURCE, MEANS FOR CONNECTING AT LEAST SAID ONE COIL TO SAID CURRENT SOURCE TO SERVE AS A POLARIZING COIL OF KNOWN EFFECTIVE LENGTH TO PROVIDE A MAGNETIC FIELD IS SAID EARTH FORMATION FOR A TIME PERIOD AT LEAST EQUAL TO THE POLARIZING TIME (T0) OF SAID FORMATION, MEANS FOR INTERRUPTING SAID POLARIZING CURRENT, AMPLIFIER MEANS, MEANS FOR CONNECTING SAID SECOND COIL TO SAID AMPLIFIER MEANS AT LEAST DURING THE INTERVAL OF TIME FOLLOWING THE INTERRUPTION OF SAID POLARIZING CURRENT, SO THAT SAID NUCLEARR MAGNETIC PRECESSION SIGNALS MAY BE DETECTED BY SAID SECOND COIL, SAID DETECTED SIGNALS COMING FROM FLUIDS CONTAINING PROTONS PRECESSING ABOUT AND RELAXING TOWARDS THE EARTH''S MAGNETIC FIELD IN PORTIONS OF SAID EARTH FORMATION THAT HAVE PREVIOUSLY BEEN TRAVERSED AND PREVIOUSLY POLARIZED AT LEAST IN PART BY THE MAGNETIC FIELD GENERATED BY POLARIZING CURRENT FLOWING THROUGH SAID EXTENSION OF SAID ONE COIL, SAID PAIR OF COILS BEING CONNECTABLE IN SERIES SO THAT SAID POLARIZING CURRENT WILL FLOW THROUGH BOTH OF SAID COILS DURING POLARIZATION OF THE FORMATION AND DISCONNECTABLE FOLLOWING INTERRUPTIONS OF SAID POLARIZING CURRENT SO THAT SAID SECOND COIL IS PERMITTED TO BE SINGLY CONNECTABLE TO SAID AMPLIFIER MEANS.