Defect discrimination apparatus, methods, and systems

1. A system, comprising:

at least a transmitter and a receiver, movable to occupy a range of depths within an inner diameter of at least two concentric pipes disposed in a geological formation; and

a controller configured to drive the transmitter to excite eddy currents in the pipes, to acquire corresponding eddy current data from the receiver, and to determine locations of defects in each of the pipes based on spatial frequency content of the eddy current data;

wherein the controller is further configured to compare the eddy current data with spectrograms stored in a memory and associated with defects of a known size and radial distance to determine the locations of defects.

2. The system according to claim 1 , wherein the transmitter comprises a time-harmonic eddy current transmitter.

3. The system according to claim 1 , wherein the transmitter and the receiver are attached to a common housing, and separated by an axial distance along the housing.

4. The system according to claim 3 , wherein the housing comprises one of a slickline tool housing, a wireline tool housing, or a drill string tool housing.

5. The system according to claim 1 , further comprising:

the memory accessible by the controller, the memory to store a database comprising predetermined relationships between a set of radial distance values associated with the locations of the defects, and a set of frequency spread bandwidth values.

6. The system according to claim 1 , further comprising:

a display coupled to the controller, the display to publish time-frequency spectrograms derived from the eddy current data in substantially real time.

7. The system according to claim 1 , wherein the controller is configured to normalize the eddy current data according to a logging speed of the receiver, to provide normalized eddy current data.

8. The system of claim 7 , wherein the controller is configured to compare the normalized eddy current data, or normalized spectrograms derived from the normalized eddy current data, with spectrograms stored in the memory and associated with defects of the known size and radial distance.

9. A method comprising:

moving a transmitter-receiver pair within at least two concentric pipes;

driving the transmitter to excite eddy currents within the at least two concentric pipes;

acquiring, by the receiver, eddy current data from the at least two concentric pipes;

determining spatial frequency content of the eddy current data; and

determining locations of defects in each of the pipes based on the spatial frequency content, wherein the locations of defects are determined based on comparing the eddy current data with spectrograms stored in a memory and associated with defects of a known size and radial distance.

10. The method according to claim 9 , further comprising:

publishing a time-frequency spectrogram derived from the eddy current data in a human-readable format, using shading or color to indicate relative signal strength.

11. The method according to claim 9 , further comprising:

retrieving information from the memory to form a comparison between the information and a time-frequency spectrogram derived from the eddy current data; and

determining at least one of a radial distance or a size associated with one or more of the defects, based on the comparison.

12. The method according to claim 9 , wherein the concentric pipes comprise at least one production pipe, at least one completion pipe, and a casing.

13. The method according to claim 9 , further comprising:

establishing a baseline signal response for the eddy current data by at least one of scanning of a section of pipe without defects or accessing a database that includes baseline data for the concentric pipes; and

subtracting the baseline signal response from the eddy current data to pre-process the eddy current data.

14. The method of claim 9 , wherein determining the locations of the defects further comprises:

determining a radial distance and azimuthal location of the defects.

15. The method of claim 14 , further comprising:

determining the radial distance based on relative permeability of at least one of the concentric pipes.

16. The method according to claim 9 , further comprising:

estimating a size of at least one of the defects based on a travel distance of a transmitter and a receiver.

17. The method according to claim 9 , further comprising:

estimating a size of at least one of the defects based on a region of impact for the transmitter-receiver pair that is used to acquire the eddy current data.

18. A method, comprising:

moving a transmitter-receiver pair within a first group of concentric pipes to acquire known defect eddy current data;

determining a frequency spread bandwidth associated with the known defect eddy current data and known defects in the first group of concentric pipes; and

storing sizes of the known defects and associated values of the frequency spread bandwidth, or values derived from the frequency spread bandwidth, as known defect information in a memory, to enable determination of unknown defect size in a second group of concentric pipes disposed in a geological formation upon access to and comparison with signals received by an inspection transmitter-receiver pair disposed in the second group.

19. The method of claim 18 , further comprising:

determining a radial distance of at least one unknown defect associated with the unknown defect size based on the known defect information.

20. The method of claim 19 , wherein determining the radial distance comprises comparing spectrograms to minimize a cost function.