Multiple-depth eddy current pipe inspection with a single coil antenna

Abstract

A method includes introducing a pipe inspection tool into a first pipe positioned within a wellbore and further positioned within at least a second pipe. The pipe inspection tool includes an electromagnetic sensor having a coil antenna that includes a coil winding extending axially along at least a portion of the electromagnetic sensor. An excitation signal is transmitted between a first terminal and a second terminal of the coil antenna. A first response signal is measured between a third terminal and a fourth terminal of the coil antenna, wherein at least one of the third and fourth terminals is different from the first and second terminals. The first response signal is then processed to determine a characteristic of the first pipe.

What is claimed is: 
     
         1 . A method, comprising:
 introducing a pipe inspection tool into a first pipe positioned within a wellbore and further positioned within at least a second pipe, the pipe inspection tool including an electromagnetic sensor having a coil antenna that includes a coil winding extending axially along at least a portion of the electromagnetic sensor;   transmitting an excitation signal between a first terminal and a second terminal of the coil antenna;   measuring a first response signal between a third terminal and a fourth terminal of the coil antenna, wherein at least one of the third and fourth terminals is different from the first and second terminals; and   processing the first response signal to determine a characteristic of the first pipe.   
     
     
         2 . The method of  claim 1 , wherein transmitting the excitation signal comprises transmitting a time-domain or frequency-domain (steady-state) signal generated by a power source electrically-coupled to the first and second terminals. 
     
     
         3 . The method of  claim 1 , wherein measuring the first response signal between the third terminal and the fourth terminal comprises receiving the first response signal with a receiver electrically-coupled to at least one of the third and fourth terminals and included in the electromagnetic sensor. 
     
     
         4 . The method of  claim 1 , further comprising:
 measuring a second response signal between a fifth terminal and a sixth terminal of the coil antenna, where an axial length of the coil antenna between the fifth and sixth terminals is longer than an axial length of the coil antenna between the third and fourth terminals; and   processing the first and second response signals to determine a characteristic of one or both of the first and the second pipes.   
     
     
         5 . The method of  claim 1 , wherein an axial length of the coil antenna between the third and fourth terminals is longer than an axial length of the coil antenna between the first and second terminals, the method further comprising processing the first response signal to determine a characteristic of the second pipe. 
     
     
         6 . The method of  claim 1 , wherein the coil winding is wound about a segmented core comprising a plurality of core segments. 
     
     
         7 . The method of  claim 6 , wherein each core segment exhibits an axial length and is axially separated from an adjacent core by a gap, and wherein the gap is at least one-fifth or more of the axial length of each adjacent core segment. 
     
     
         8 . A method, comprising:
 introducing a pipe inspection tool into a first pipe positioned within a wellbore and further positioned within at least a second pipe, the pipe inspection tool including an electromagnetic sensor having a coil antenna that includes a coil winding extending axially along at least a portion of the electromagnetic sensor;   transmitting a first excitation signal between a first terminal and a second terminal of the coil antenna;   measuring a first response signal between the first and second terminals;   transmitting a second excitation signal between a third terminal and a fourth terminal of the coil antenna, where the third and fourth terminals are different from the first and second terminals;   measuring a second response signal between the third and fourth terminals; and   processing the first and second signals to determine a characteristic of one or both of the first and second pipes.   
     
     
         9 . The method of  claim 8 , wherein transmitting the first excitation signal comprises transmitting a first time-domain or frequency-domain (steady-state) signal generated by a first power source electrically-coupled to the first and second terminals, and
 wherein transmitting the second excitation signal comprises transmitting a second time-domain or frequency-domain (steady-state) signal generated by a second power source electrically-coupled to the third and fourth terminals.   
     
     
         10 . The method of  claim 8 , wherein measuring the first response signal between the first terminal and the second terminal comprises receiving the first response signal with a first receiver electrically-coupled to the first and second terminals and included in the electromagnetic sensor, and
 wherein measuring the second response signal between the third terminal and the fourth terminal comprises receiving the second response signal with a second receiver electrically-coupled to the third and fourth terminals and included in the electromagnetic sensor.   
     
     
         11 . The method of  claim 8 , wherein the coil winding is wound about a segmented core comprising a plurality of core segments. 
     
     
         12 . The method of  claim 11 , wherein each core segment exhibits an axial length and is axially separated from an adjacent core by a gap, and wherein the gap is at least one-fifth or more of the axial length of each adjacent core segment. 
     
     
         13 . A method, comprising:
 introducing a pipe inspection tool into a first pipe positioned within a wellbore and further positioned within at least a second pipe, the pipe inspection tool including an electromagnetic sensor having a coil antenna that includes a coil winding extending axially along at least a portion of the electromagnetic sensor;   transmitting a first excitation signal between a first terminal and a second terminal of the coil antenna;   measuring a first response signal between the first and second terminals;   measuring a second response signal between the second terminal and a third terminal of the coil antenna;   summing the first and second response signals to obtain a summed response signal indicative of a measurement between the first and third terminals; and   processing the summed response signal to determine a characteristic of at least one of the first and second pipes.   
     
     
         14 . The method of  claim 13 , further comprising:
 subtracting the first and second response signals to obtain a difference response; and   processing the difference response to determine the characteristic of at least one of the first and second pipes.   
     
     
         15 . The method of  claim 13 , wherein transmitting the excitation signal comprises transmitting a time-domain or frequency-domain (steady-state) signal generated by a power source electrically-coupled to the first and second terminals. 
     
     
         16 . The method of  claim 13 , wherein measuring the first response signal between the first terminal and the second terminal comprises receiving the first response signal with a first receiver electrically-coupled to the first and second terminals and included in the electromagnetic sensor, and
 wherein measuring the second response signal between the second terminal and the third terminal comprises receiving the second response signal with a second receiver electrically-coupled to the second and third terminals and included in the electromagnetic sensor.   
     
     
         17 . The method of  claim 13 , wherein the coil winding is wound about a segmented core comprising a plurality of core segments. 
     
     
         18 . The method of  claim 17 , wherein each core segment exhibits an axial length and is axially separated from an adjacent core by a gap, and wherein the gap is at least one-fifth or more of the axial length of each adjacent core segment. 
     
     
         19 . A method, comprising:
 introducing a pipe inspection tool into a first pipe positioned within a wellbore and further positioned within at least a second pipe, the pipe inspection tool including an electromagnetic sensor having a coil antenna that includes a coil winding extending axially along at least a portion of the electromagnetic sensor;   selecting a number of consecutive terminals on the coil antenna;   transmitting an excitation signal between each neighboring terminal of the consecutive terminals of the coil antenna;   receiving and recording a corresponding response signal for each excitation signal between each neighboring terminal;   adding a subset of the response signals for each excitation signal between any two terminals of the number of consecutive terminals to obtain a synthesized signal; and   processing the synthesized signal to determine a characteristic of at least one of the first and second pipes.   
     
     
         20 . The method of  claim 19 , further comprising:
 combining the subset of the response signals for each excitation signal between any two terminals by one of addition, subtraction, or a weighted sum, where weights of the weighted sum are positive or negative numbers; and   processing the synthesized signal to determine the characteristic of at least one of the first and second pipes.   
     
     
         21 . The method of  claim 19 , wherein the coil winding is wound about a segmented core comprising a plurality of core segments. 
     
     
         22 . The method of  claim 21 , wherein each core segment exhibits an axial length and is axially separated from an adjacent core by a gap, and wherein the gap is at least one-fifth or more of the axial length of each adjacent core segment.