System located in drill string for well logging while drilling
First Claim
1. The method of measuring while drilling the magnetic fields produced by a current flowing in or around an electrically contrasting target to permit continuous determination of the location of the target with respect to a deep well being drilled, comprising:
- securing a magnetic field sensor within a nonmagnetic drill string section forming a part of, and located near the bottom of, a drill string;
aligning the sensor with respect to a drill bit in said drill string;
positioning an electrode within said drill string, said electrode being spaced above said sensor section;
supplying alternating current to said electrode;
causing said alternating current to flow from said electrode into said drill string;
said drill string being sufficiently electrically resistive to cause said alternating current to be injected into the earth surrounding the well being drilled, thereby to produce an alternating current flow in said earth, said earth current flow being substantially uniformly distributed around said drill string but being distorted by targets of contrasting electrical conductivity located in said earth, said targets causing a perterbation of the alternating electrical current flow;
measuring with said sensor the alternating magnetic field produced in the earth by said alternating current flow whereby the distance and direction of said target from said sensor can be determined.
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Accused Products
Abstract
Logging apparatus for measuring magnetic fields while drilling is disclosed. An electrode is located within a drill string and receives alternating current which is conducted to the drill string and from the drill string is injected into the earth surrounding the well. This current is concentrated in anomalies of interest, such as the casing of a target well which is to be intercepted by, or to be avoided by, the well being drilled. A sensitive magnetometer is located within a nonmagnetic portion of the drill string, near the bottom thereof, to detect the alternating magnetic field generated by the current flow in the target and to produce output signals corresponding to the detected field. The output from the magnetometer is used to determine the relative locations of the well being drilled and the target.
123 Citations
23 Claims
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1. The method of measuring while drilling the magnetic fields produced by a current flowing in or around an electrically contrasting target to permit continuous determination of the location of the target with respect to a deep well being drilled, comprising:
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securing a magnetic field sensor within a nonmagnetic drill string section forming a part of, and located near the bottom of, a drill string; aligning the sensor with respect to a drill bit in said drill string; positioning an electrode within said drill string, said electrode being spaced above said sensor section; supplying alternating current to said electrode; causing said alternating current to flow from said electrode into said drill string;
said drill string being sufficiently electrically resistive to cause said alternating current to be injected into the earth surrounding the well being drilled, thereby to produce an alternating current flow in said earth, said earth current flow being substantially uniformly distributed around said drill string but being distorted by targets of contrasting electrical conductivity located in said earth, said targets causing a perterbation of the alternating electrical current flow;measuring with said sensor the alternating magnetic field produced in the earth by said alternating current flow whereby the distance and direction of said target from said sensor can be determined. - View Dependent Claims (2, 3, 4, 5, 6)
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7. Logging apparatus for measuring while drilling magnetic fields produced by alternating current flow in an electrically conductive target to permit continuous determination of the location of the target with respect to a deep well being drilled, comprising:
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a magnetic field sensor; means for mounting said sensor coaxially within a nonmagnetic section for a drill string; an electrode; means for positioning said electrode within the same drill string in which said sensor is mounted; means for supplying alternating current to said electrode for injecting said current into the earth surrounding a well, so that the injected current can be collected in a target of contrasting electrical conductivity to produce a target alternating magnetic field detectable by said sensor.
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8. Logging apparatus for measuring while drilling the magnetic fields produced by alternating current flow in target of contrasting electrical conductivity to provide data relating the location of the target with respect to a well being drilled, comprising:
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a drill string carrying a drill bit for drilling a well; an electrode section forming a part of said drill string; an electrode; means positioning said electrode within said electrode section; a source of alternating current; means supplying said alternating current to said electrode so that said current flows into said drill string and is injected into the earth surrounding said well, said alternating earth current being distributed around said well but being collected by any nearby target of contrasting electrical conductivity to produce a perterbed electricurrent flow; a nonmagnetic sensor section forming a part of said drill string and being spaced below said electrode section; magnetic field sensor means; mounting means locating said sensor means within said sensor section, said sensor being responsive to measure the alternating target magnetic field produced by said perterbed current flow, whereby the distance and direction of said target with respect to said sensor can be determined. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification