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Method for determining the location of a deep-well casing by magnetic field sensing

  • US 4,700,142 A
  • Filed: 04/04/1986
  • Issued: 10/13/1987
  • Est. Priority Date: 04/04/1986
  • Status: Expired due to Term
First Claim
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1. A method of locating from a first underground location the distance and direction of a second, target underground location, comprising:

  • partially drilling a borehole at a location spaced from said target location;

    determining, at selected depth intervals, the inclination of said borehole;

    producing an alternating current flow at said target location to produce an AC magnetic field;

    lowering into said borehole a sensor tool having a longitudinal axis, said sensor tool carrying first and second AC magnetic field detectors and first and second gravity detectors;

    measuring, by means of said AC magnetic field detectors, the vector components of said AC magnetic field projected onto a reference plane perpendicular to said longitudinal axis;

    measuring, by means of said first and second gravity detectors, two components of the earth'"'"'s gravitational field projected onto said reference plane;

    determining, from said AC field vector components, the direction and magnitude of said AC magnetic field with respect to said sensor tool;

    determining, from said components of the earth'"'"'s gravitational field and from the inclination of said borehole, the orientation of said sensor tool; and

    determining from the orientation of said sensor tool, the direction and magnitude in space of said AC magnetic field and thereby the direction and distance of said target location from said sensor tool.

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