Method and apparatus for well-bore proximity measurement while drilling
First Claim
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1. A method of determining a distance to a first borehole from a second borehole, the method comprising:
- producing a time varying magnetic field in the first borehole by rotating a magnet in the second borehole at a first rotational speed and inducing a magnetization in a magnetic object in the first borehole;
rotating a coil in the second borehole synchronously with the magnet for producing a signal responsive to a magnetic flux resulting from the magnetization;
removing a component of the signal, wherein the component is at twice the rotational speed and due to earth'"'"'s magnetic field; and
estimating the distance using a remainder of the signal at twice the rotational speed.
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Abstract
A rotating, transversely magnetized, magnet on a drill collar induces magnetization in a casing of a preexisting well. A coil rotating synchronously with the magnet produces a current at twice the frequency of rotation and having an amplitude that depends upon the distance from the magnet to the preexisting well. Alternatively, a variable magnetic field is produced in the casing using a switchable magnet.
54 Citations
24 Claims
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1. A method of determining a distance to a first borehole from a second borehole, the method comprising:
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producing a time varying magnetic field in the first borehole by rotating a magnet in the second borehole at a first rotational speed and inducing a magnetization in a magnetic object in the first borehole; rotating a coil in the second borehole synchronously with the magnet for producing a signal responsive to a magnetic flux resulting from the magnetization; removing a component of the signal, wherein the component is at twice the rotational speed and due to earth'"'"'s magnetic field; and estimating the distance using a remainder of the signal at twice the rotational speed. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of determining a distance to a first borehole from a second borehole, the method comprising:
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producing transient magnetic field in the first borehole by switching a polarity of a magnet having a substantially longitudinal magnetization in the second borehole and inducing a transient magnetization of a magnetic object in the first borehole, using a coil in the second borehole for producing a signal responsive to a magnetic flux resulting from the induced magnetization; and estimating the distance using a portion of the signal substantially excluding a component due to eddy currents in a formation and eddy currents in a conductive body in the second borehole. - View Dependent Claims (9, 10, 11)
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12. An apparatus configured to determine a distance to a first borehole from a second borehole, the apparatus comprising:
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(a) a magnet configured to be conveyed in the second borehole, rotate at a first rotational speed, produce a time varying magnetic field in the first borehole and induce a magnetization in a magnetic object in the first borehole; (b) a coil in the second borehole configured to rotate synchronously with the magnet and produce a signal responsive to a magnetic flux resulting from the magnetization; and (c) a processor configured to; removing a component of the signal, wherein the component is at twice the rotational speed and due to earth'"'"'s magnetic field, and estimate the distance using a remainder of the signal at twice the rotational speed. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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20. An apparatus configured to determine a distance from a first borehole to a second borehole, the apparatus comprising:
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(i) a switchable magnet having a substantially longitudinal magnetization in the second borehole configured to produce a transient field in the first borehole and induce a transient magnetization in a magnetic object in the first borehole; (ii) a coil in the second borehole configured to produce a signal responsive to a magnetic flux resulting from the magnetization; and (iii) a processor configured to estimate the distance using a portion of the signal substantially excluding a component due to eddy currents in a formation and eddy currents in a conductive body in the second borehole. - View Dependent Claims (21, 22, 23)
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24. A non-transitory computer-readable medium product having stored thereon instructions that when read by at least one processor cause the at least one processor to perform a method, the method comprising:
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producing a time varying magnetic field in a first borehole by rotating a magnet in a second borehole at a first rotational speed and inducing a magnetization in a magnetic object in the first borehole; rotating a coil in the second borehole synchronously with the magnet for producing a signal responsive to a magnetic flux resulting from the magnetization; removing a component of the signal, wherein the component is at twice the rotational speed and due to earth'"'"'s magnetic field; and estimating the distance using a remainder of the signal at twice the rotational speed.
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Specification