Method of determining the location of a deep-well casing by magnetic field sensing
First Claim
1. A method of locating a target borehole containing an electrically conductive material or object such as a casing, drill stem, or the like and for directing the drilling of a relief borehole to intersect the target borehole, comprising:
- partially drilling a relief borehole at a location spaced from said target borehole;
lowering into said relief borehole at least one electrode adapted to inject current into the earth surrounding said relief borehole;
connecting a source of low frequency current to said electrode, thereby producing a low frequency alternating electric current flow in the conductive material located in said target borehole, the current flow in said target borehole conductive material producing a target magnetic field;
measuring at selected depth intervals the magnitude, phase and direction of the target magnetic field produced within said relief borehole by the electric current flow in the conductive material in said target borehole;
measuring at said selected depth intervals the magnitude and direction of the earth'"'"'s magnetic field;
determining from said target borehole magnetic field measurements and said earth'"'"'s magnetic field measurements at each selected depth interval the compass direction and distance of said target borehole; and
further drilling said relief borehole so that it intersects said target borehole at a selected depth below the earth'"'"'s surface.
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Accused Products
Abstract
A method of locating a deep well casing at substantial distances below the earth'"'"'s surface, and for directing the drilling of a second relief well to intersect the first well at substantial distances below the earth'"'"'s surface is disclosed. A low frequency alternating electric current flow is produced in the casing of the well to be detected by means of current injected into the earth surrounding the first well. The current flow in the casing produces a magnetic field which is detectable by a sensitive magnetic field sensor suspended in the relief hole and spaced a substantial distance from the current source. The magnetic field sensor detects the magnitude and apparent direction of the alternating field, and this measurement is combined with a concurrent measurement of the earth'"'"'s magnetic field to determine the direction and distance of the casing from the relief well. This information is then used to direct the continued drilling of the relief well, with periodic measurements being made to provide directional control of the drilling so that the first well is intersected at the desired depth below the earth'"'"'s surface.
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Citations
8 Claims
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1. A method of locating a target borehole containing an electrically conductive material or object such as a casing, drill stem, or the like and for directing the drilling of a relief borehole to intersect the target borehole, comprising:
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partially drilling a relief borehole at a location spaced from said target borehole; lowering into said relief borehole at least one electrode adapted to inject current into the earth surrounding said relief borehole;
connecting a source of low frequency current to said electrode, thereby producing a low frequency alternating electric current flow in the conductive material located in said target borehole, the current flow in said target borehole conductive material producing a target magnetic field;measuring at selected depth intervals the magnitude, phase and direction of the target magnetic field produced within said relief borehole by the electric current flow in the conductive material in said target borehole; measuring at said selected depth intervals the magnitude and direction of the earth'"'"'s magnetic field; determining from said target borehole magnetic field measurements and said earth'"'"'s magnetic field measurements at each selected depth interval the compass direction and distance of said target borehole; and further drilling said relief borehole so that it intersects said target borehole at a selected depth below the earth'"'"'s surface. - View Dependent Claims (2, 3, 4, 5, 6)
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7. Apparatus for locating a target cased borehole or uncased borehole containing a drill stem or other electrically conductive object and for directing the drilling of a relief borehole to intersect the target borehole, comprising:
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a first electrode in contact with the ground at the surface of the earth near the well head of said relief borehole; a wireline for said relief borehole; a second electrode adapted to contact the ground at a selected depth within said relief borehole, said second electrode being supported by said wireline; a magnetic field sensor supported by said wireline, said magnetic field sensor being located within said relief borehole below said second electrode a distance sufficient to substantially reduce the effect of magnetic fields due to ground currents from said second electrode; means for supplying between said first and second electrodes an alternating potential of low frequency to produce a ground current between said electrodes, said ground current being short circuited by said target borehole conductor to produce a target magnetic field detectable by said magnetic field sensor; and protective means at said magnetic field sensor for short circuiting any ground currents within said relief well to prevent such relief well currents from affecting said magnetic field sensor. - View Dependent Claims (8)
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Specification