Extra bucking coils as an alternative way to balance induction arrays

Abstract

An electromagnetic logging tool is disclosed that includes a support; and at least one four-coil array disposed on the support, wherein the at least one four-coil array comprises: a transmitter, a bucking coil, a receiver, and a trim coil. A method for balancing an induction array is disclosed that includes applying an alternating current to a transmitter of the induction array that comprises the transmitter, a bucking coil and a receiver; measuring a mutual coupling between the transmitter and the receiver; and adding an extra bucking coil, if the mutual coupling exceeds a selected criterion.

1 - 8 . (canceled) 
   
   
       9 . A method for balancing an induction array, comprising:
 applying an alternating current to a transmitter of the induction array that comprises the transmitter, a bucking coil and a receiver;   measuring a mutual coupling between the transmitter and the receiver; and   adding an extra bucking coil, if the mutual coupling exceeds a selected criterion.   
   
   
       10 . The method of  claim 9 , further comprising:
 measuring again the mutual coupling between the transmitter and the receiver; and   adjusting the extra bucking coil, if the mutual coupling exceeds the selected criterion.   
   
   
       11 . The method of  claim 9 , wherein a location for adding the extra bucking coil is based on a magnitude of the mutual coupling. 
   
   
       12 . The method of  claim 9 , wherein a number of turns of the extra bucking coil is based on a magnitude of the mutual coupling. 
   
   
       13 . The method of  claim 9 , wherein the selected criterion is the imaginary signal (σ x ) portion is less than one hundred times a tolerance in real signal (Δσ R ).