Method for determining the location of a deep-well casing by magnetic field sensing
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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Abstract
Logging apparatus for measuring alternating magnetic fields generated by electric current flow on a subterranean target near a borehole is disclosed. Electric current of a predetermined temporal form is made to flow on the target; the resulting magnetic field is measured by magnetometers in a downhole sonde. The orientation of the sonde is fixed by various combinations of gyroscope, accelerometer, magnetometer measurements, and borehole survey data.
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Citations
10 Claims
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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:
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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. - View Dependent Claims (2, 3, 4)
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5. Apparatus for locating from a first underground location the distance and direction to a second, electrically conductive, target underground location, comprising:
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an electrode in contact with the earth for injecting current therein to produce an alternating current in said target location, said target location current producing an AC magnetic field in the surrounding earth; sensor means at said first underground location, said sensor means having a longitudinal axis and including; (a) first and second AC magnetic field detectors having x and y axes of sensitivity in a reference plane perpendicular to the longitudinal axis of said sensor means and producing first and second output signals representing x and y vector components of said AC magnetic field projected on said plane; (b) first and second gravitational field detectors having x and y axes of sensitivity and producing third and fourth output signals representing x and y vector components of the earth'"'"'s gravitational field projected on said plane; and (c) circuit means connected to said detectors for receiving said output signals sequentially and for transmitting said signals; receiver means connected to said sensor means for receiving signals transmitted thereby; and computer means connected to said receiver means for processing said first, second, third and fourth output signals to calculate the horizontal direction and distance of said target from said sensor. - View Dependent Claims (6)
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7. A method of locating from a first underground location the distance and direction to a second, target underground location, comprising:
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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, at least one gravity detector, and at least one static magnetic field detector; measuring, by means of said first and second AC magnetic field detectors, first and second vector components of said magnetic field projected onto a reference plane perpendicular to said longitudinal axis; measuring, by means of said gravity detector, one component of the earth'"'"'s gravitational field projected onto said reference plane; measuring, by means of said static magnetic field detector, one component of the earth'"'"'s static magnetic 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 field; determining, from said component of the earth'"'"'s gravitational field, from said component of the earth'"'"'s static magnetic 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. - View Dependent Claims (8, 9, 10)
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Specification