Eddy current method and apparatus for inspecting ferromagnetic tubular members
First Claim
1. Apparatus for locating and evaluating defects in ferromagnetic casing comprising:
- an elongated body adapted for suspension in said casing from a well logging cable;
first means, adapted to be disposed within said casing, and located on said body, for generating an alternating magnetic field along a portion of the longitudinal axis of said casing which induces circumferential currents therein;
second means, adapted to be disposed within said casing and located on said body, said second means disposed axially from said first means, for generating at least one signal in response to perturbations of said circumferential current in said casing, said second means including;
a carrying member,a first coil having N number of windings supported by said carrying member,a second coil disposed adjacent said first coil and having 2 N number of windings serially opposed to the windings of said first coil, anda third coil disposed adjacent said second coil and having N number of windings serially opposed to the windings of said second coil; and
a signal processor coupled to said second means for receiving at least one of said signals for measuring the amplitude and phase components thereof, thereby determining the characteristics of said defect.
0 Assignments
0 Petitions
Accused Products
Abstract
Casing inspection apparatus and method are disclosed for determining defects and other anomalies in ferromagnetic oil well casing. The inspection apparatus utilizes a pair of coaxial transmitter coils for generating an alternating magnetic field in the casing thereby inducing circumferential currents in the casing wall. These circumferential currents and the magnetic field associated with the currents are perturbed by corrosion, holes, and other anomalies both inside and outside the casing wall. Differential receiver coils are urged in proximity with the casing wall to generate a differential receiver signal in response to such perturbations in the magnetic field. The differential receivers are provided with three coils serially connected and having N, 2N and N winding turns respectively. The windings of the coils are disposed in adjacent relationship to one another and wound in a direction opposite to the adjacent winding. The casing inspection apparatus achieves enhanced sensitivity to small defects and reduced sensitivity to magnetic anomalies by processing both the amplitude and phase components of the receiver signal.
109 Citations
32 Claims
-
1. Apparatus for locating and evaluating defects in ferromagnetic casing comprising:
-
an elongated body adapted for suspension in said casing from a well logging cable; first means, adapted to be disposed within said casing, and located on said body, for generating an alternating magnetic field along a portion of the longitudinal axis of said casing which induces circumferential currents therein; second means, adapted to be disposed within said casing and located on said body, said second means disposed axially from said first means, for generating at least one signal in response to perturbations of said circumferential current in said casing, said second means including; a carrying member, a first coil having N number of windings supported by said carrying member, a second coil disposed adjacent said first coil and having 2 N number of windings serially opposed to the windings of said first coil, and a third coil disposed adjacent said second coil and having N number of windings serially opposed to the windings of said second coil; and a signal processor coupled to said second means for receiving at least one of said signals for measuring the amplitude and phase components thereof, thereby determining the characteristics of said defect. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
-
-
18. Apparatus for locating and evaluating defects in ferromagnetic casing comprising:
-
an elongated body adapted for suspension in said casing from a well-logging cable; at least one coaxial transmitter coil adapted to be positioned within said casing on said body, for generating an alternating magnetic field along a portion of the longitudinal axis thereby inducing circumferential currents in said casing; and at least one array of differential receiver coils located on said body and adapted to be disposed within said casing in spaced axial relationship to said coaxial transmitter coil, for generating a signal in response to perturbations of said circumferential currents in said casing, wherein each of said differential receiver coils includes; a carrying member; a first coil having N number of windings supported by said carrying member; a second coil disposed adjacent said first coil having 2N number of windings serially opposed to said windings of said first coil; and a third coil disposed adjacent said second coil having N number of windings serially opposed to said windings of said second coil.
-
-
19. Apparatus for locating and evaluating defects in ferromagnetic oil well bore casing comprising:
-
an elongated body adapted for suspension in said casing from a well-logging cable; at least one coaxial transmitter coil located on said body and adapted to be positioned within said casing, driven by an alternating current source, for generating an alternating magnetic field, said magnetic field inducing circumferential currents in said casing; and first and second arrays of differential receiver coils located on said body and adapted to be disposed within said casing in spaced axial relationship to said coaxial transmitter coil, for generating at least one signal in response to perturbations in said circumferential currents, each of said differential receiver coils are enclosed in a receiver pad and include; a carrying member; a first coil having N number of windings disposed within said carrying member; a second coil disposed adjacent said first coil having 2N number of windings serially opposed to said windings of said first coil; and a third coil disposed adjacent said second coil having N number of windings serially opposed to said windings of said second coil.
-
-
20. Apparatus for locating and evaluating defects in ferromagnetic casing comprising:
-
an elongated body adapted for suspension in said casing from a well-logging cable; first means, adapted to be disposed within said casing, and located on said body, for generating an alternating magnetic field along a portion of the longitudinal axis of said casing which induces circumferential currents therein; second means, adapted to be disposed within said casing and located on said body, said second means in spaced axial relationship with said first means, for generating at least one signal in response to perturbations of said circumferential currents in said casing, said second means including a carrying member, and three coils disposed thereon, said coils located in adjacent relationship to one another and having N, 2N, and N number of windings respectively, said coils electrically connected in a serial manner forming a differential coil pair.
-
-
21. A method of distinguishing actual defects in ferromagnetic casing from magnetic anomalies comprising the steps of:
-
generating a first alternating magnetic field in the casing thereby inducing circumferential currents in said casing; receiving a measured phase signal from a differential receiver coil arrangement in close proximity to said casing wall, said differential receiver coil arrangement being spaced axially from the source of said first alternating magnetic field; receiving a phase reference signal from a reference coaxial coil disposed axially from said source of first alternating magnetic field; generating a phase difference signal between said measured phase signal and said reference phase signal; and identifying actual defects from the shape of said phase difference signal, where a phase change from substantially 0°
toward -90° and
then through 0°
toward +90° and
then through 0°
degrees toward -90° and
back to substantially 0°
indicates a real defect, and where the phase difference signal changes from substantially 0°
degrees toward -90° and
then back toward substantially 0°
indicates a magnetic anomaly. - View Dependent Claims (22, 23, 24, 26, 27, 28, 29)
-
-
25. A receiver coil arrangement for detecting defects in ferromagnetic oil well casing comprising:
-
a non-conductive carrying member; first, second and third multiple turn conductive coils disposed on said carrying member having N, 2N, and N number of windings respectively, said coils in adjacent relationship to one another, with each of said coils wound in the same direction and electrically connected in series such that an induced current circulating in said coil having 2N turns flows in a direction opposite to induced currents flowing in said coils having N turns.
-
-
30. A receiver coil arrangement for detecting defects in ferromagnetic oil well casings comprising:
-
a non-conductive carrying member; a first coil having N number of windings supported by said carrying member; a second coil disposed adjacent said first coil and having 2N number of windings serially opposed to the windings of said first coil; and a third coil disposed adjacent said second coil and having N number of windings serially opposed to the windings of said second coil.
-
-
31. A method of distinguishing actual defects in ferromagnetic casing from magnetic anomalies comprising the steps of:
-
generating a first alternating magnetic field in the casing thereby inducing circumferential currents in said casing; receiving a measured phase signal from a differential receiver coil arrangement in close proximity to said casing wall, said differential receiver coil arrangement being spaced axially from the source of said first alternating magnetic field; receiving a phase reference signal from a reference coaxial coil disposed axially from said source of first alternating magnetic field; generating a phase difference signal between said measured phase signal and said reference phase signal; and identifying actual defects from the shape of said phase difference signal, where one unidirectional phase pulse indicates a magnetic anomaly, and where at least two pulses of opposite polarity indicates a real defect.
-
-
32. A method of distinguishing actual defects in ferromagnetic casing from magnetic anomalies comprising the steps of:
-
generating a first alternating magnetic field in the casing thereby inducing circumferential currents in said casing; receiving a measured phase signal from a differential receiver coil arrangement in close proximity to said casing wall, said differential receiver coil arrangement being spaced axially from the source of said first alternating magnetic field; receiving a phase reference signal from a reference coaxial coil disposed axially from said source of first alternating magnetic field; generating a phase difference signal between said measured phase signal and said reference phase signal; receiving a measured amplitude signal from said differential receiver coil arrangement; multiplying said amplitude signal by said phase difference signal to generate an identification signal; and identifying actual defects from the shape of said phase difference signal, where a phase change from substantially 0°
toward -90° and
then through 0°
toward +90° and
then through 0°
toward -90° and
back to substantially 0°
indicates a real defect, and where the phase difference signal changes from substantially 0°
toward -90° and
then back toward substantially 0°
indicates a magnetic anomaly.
-
Specification