Apparatus for locating an elongated conductive body by electromagnetic measurement while drilling
First Claim
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1. An electromagnetic detection system for locating, from a borehole being drilled, an underground elongated conductive body, comprising:
- a borehole;
a drill stem within said borehole;
an elongated conductive body located in the earth near said borehole;
a source toroidal inductor including a toroidal winding, said source inductor being mounted on and surrounding said drill stem and inductively coupled thereto;
AC source means connected to said toroidal winding to energize said source inductor with alternating current, said winding acting as the primary of a transformer to induce a secondary current in a transformer secondary including said drill stem, the earth surrounding said borehole, and said conductive body;
magnetic field sensor means including a pair of solenoidal detectors each including a core and a winding surrounding said core, said detector being mounted on opposite sides of said drill stem so as to be responsive to secondary magnetic fields generated by said secondary current flowing in said conductive body but essentially nonresponsive to magnetic fields generated by secondary current flowing in said drill stem;
circuit means connected to said sensor means, including means producing a data signal corresponding to any sensor output;
means mounted on said drill stem producing signals indicating the orientation of said drill stem; and
means for transmitting said data signals and said orientation signals to the surface of the earth.
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Abstract
A method and apparatus for determining the distance and direction of a well from a borehole. A toroidal inductor surrounds a drill stem within a borehole. The inductor acts as a primary for a transformer, with the drill stem, the earth surrounding the borehole, and electrically conductive material at the target well forming a single loop transformer secondary. An oscillator is connected to the primary to produce an induced AC current in the secondary. Secondary current flowing in the target well produces an AC secondary magnetic field which is detected at the borehole.
363 Citations
28 Claims
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1. An electromagnetic detection system for locating, from a borehole being drilled, an underground elongated conductive body, comprising:
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a borehole; a drill stem within said borehole; an elongated conductive body located in the earth near said borehole; a source toroidal inductor including a toroidal winding, said source inductor being mounted on and surrounding said drill stem and inductively coupled thereto; AC source means connected to said toroidal winding to energize said source inductor with alternating current, said winding acting as the primary of a transformer to induce a secondary current in a transformer secondary including said drill stem, the earth surrounding said borehole, and said conductive body; magnetic field sensor means including a pair of solenoidal detectors each including a core and a winding surrounding said core, said detector being mounted on opposite sides of said drill stem so as to be responsive to secondary magnetic fields generated by said secondary current flowing in said conductive body but essentially nonresponsive to magnetic fields generated by secondary current flowing in said drill stem; circuit means connected to said sensor means, including means producing a data signal corresponding to any sensor output; means mounted on said drill stem producing signals indicating the orientation of said drill stem; and means for transmitting said data signals and said orientation signals to the surface of the earth. - View Dependent Claims (2, 3, 4, 5)
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6. An electromagnetic detection system for locating, from a borehole being drilled, an underground elongated conductive body, comprising:
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a borehole; a drill stem within said borehole; an elongated conductive body located in the earth near said borehole; a source toroidal inductor including a toroidal winding, said source inductor being mounted on and surrounding said drill stem and inductively coupled thereto; AC source means connected to said toroidal winding to energize said source inductor with alternating current, said winding acting as the primary of a transformer to induce a secondary current in a transformer secondary including said drill stem, the earth surrounding said borehole, and said conductive body; magnetic field sensor means comprising first and second sensors, each said sensor having an axis of maximum sensitivity, the axes of maximum sensitivity being at right angles to each other and to a longitudinal axis of said drill stem, said sensor means being mounted on said drill stem so as to be responsive to secondary magnetic fields generated by said secondary current flowing in said conductive body but essentially nonresponsive to magnetic fields generated by secondary current flowing in said drill stem; circuit means connected to said sensor means, including means producing a data signal corresponding to any sensor output; means mounted on said drill stem producing signals indicating the orientation of said drill stem; and means for transmitting said data signals and said orientation signals to the surface of the earth. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. An electromagnetic detecting system for locating, from a borehole being drilled, an underground elongated conductive body, comprising:
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a borehole; a drill stem within said borehole; an elongated conductive body located in the earth near said borehole; a first source toroidal inductor including a toroidal winding, said source inductor being mounted on and surrounding said drill stem and inductively coupled thereto; first AC source means connected to said toroidal winding to energize said source inductor with alternating current, said winding acting as the primary of a transformer to induce a secondary current in a transformer secondary including said drill stem, the earth surrounding said borehole, and said conductive body; a second source inductor mounted on said drill stem, said second inductor comprising first and second solenoids having parallel axes and mounted on opposite sides of said drill stem; second AC source means having a frequency different from the frequency of said first AC source means and drivingly connected to said solenoids to produce a solenoidal primary magnetic field in the earth surrounding said borehole, said solenoidal primary producing a current at the frequency of said second AC source in said conductive body, which produces a secondary magnetic field at said AC second source frequency in the earth surrounding said borehole; magnetic field sensor means mounted on said drill stem so as to be responsive to secondary magnetic fields generated by said secondary currents flowing in said conductive body but essentially nonresponsive to magnetic fields generated by secondary currents flowing in said drill stem; circuit means connected to said sensor means, including means producing a data signal corresponding to any sensor output; means mounted on said drill stem producing signals indicating the orientation of said drill stem; and means for transmitting said data signals and said orientation signals to the surface of the earth. - View Dependent Claims (17, 18, 19, 20)
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21. An electromagnetic detection system for locating, from a borehole being drilled in the earth, an underground elongated conductive body, comprising:
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a borehole; an elongated drill stem having a longitudinal axis and located within said borehole, said drill stem carrying at the bottom of the borehole a rotatable drill head; an elongated conductive body located in the earth near said borehole; a primary field solenoidal inductor mounted on said drill stem adjacent said drill head; an AC source operating at a first frequency drivingly connected to said solenoidal inductor to produce a primary magnetic field alternating at said first frequency in the earth surrounding said borehole, at least a part of said primary field intersecting said elongated conductive body to produce therein a secondary current flow at said first frequency, said secondary current flow producing a secondary magnetic field at said first frequency; first and second magnetic field sensors mounted on said drill stem at a location spaced from and above said solenoidal inductor, said first and second sensors each having an axis of maximum sensitivity, and having their axes at right angles to each other and to said longitudinal axis of said drill stem, said sensors being responsive to vector components of said secondary magnetic field which are parallel to said axes of maximum sensitivity to produce corresponding sensor output signals; bandpass means connected to said first and second sensors to restrict the output thereof to signals having said first frequency; a toroidal source inductor mounted on said drill stem; to said toroidal inductor to produce a current flow in said drill stem at said second frequency; a toroidal current sensor mounted on said drill stem adjacent said toroidal source inductor and responsive to current flow in said drill stem to produce a corresponding toroidal sensor output; bandpass means connected to said toroidal sensor for restricting said toroidal sensor output to said second frequency; multiplexer means for selecting each of said sensor outputs sequentially; and circuit means for transmitting said outputs.
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22. An electromagnetic measurement while drilling system for locating, from a borehole being drilled, an underground target elongated conductive body, comprising:
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a borehole being drilled and having an axis, said borehole containing a drill stem and a rotatable drill bit mounted axially therein; an elongated target conductive body in the earth near said borehole; a source solenoid including a core and a solenoidal winding surrounding said core mounted on said drill stem near said drill bit, said source solenoid having an axis perpendicular to the axis of said borehole; means energizing said source solenoid with alternating current to produce a magnetic field in the earth surrounding said borehole and to thereby produce a current in said conductive body; sensor means mounted on said drill stem to detect secondary magnetic fields generated by said current in said conductive body; circuit means connected to said sensor means, including means producing a data signal corresponding to any sensor output; and means transmitting said data signals to the surface of the earth. - View Dependent Claims (23, 24, 25, 26, 27, 28)
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Specification