Elongated coil assembly for electromagnetic borehole surveying
First Claim
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1. Apparatus for guiding the drilling of a borehole in the earth in spaced relationship to a guide borehole in the earth, comprising:
- a coil assembly incorporating an elongated core carrying a longitudinal coil winding located in the guide borehole;
a source of current connected to said coil to produce a magnetic field in the earth surrounding the guide borehole and in the region of the borehole being drilled;
sensors in said borehole being drilled for detecting vectors of gravity and of the generated magnetic field; and
a controller responsive to the generated magnetic field and the measured magnetic field vectors to control the direction of further drilling.
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Abstract
An apparatus and method for surveying the path of a borehole includes three single-axis electromagnetic field sensors and three single axis gravity direction sensors in the borehole being surveyed. A pair of closely spaced, parallel guide wires carrying oppositely directed electric current in a reference borehole generate a known electromagnetic field, which is detected by the sensors. Mathematical analysis of electromagnetic and gravity measurements determines the lateral location and the direction of drilling in the neighboring borehole.
53 Citations
12 Claims
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1. Apparatus for guiding the drilling of a borehole in the earth in spaced relationship to a guide borehole in the earth, comprising:
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a coil assembly incorporating an elongated core carrying a longitudinal coil winding located in the guide borehole;
a source of current connected to said coil to produce a magnetic field in the earth surrounding the guide borehole and in the region of the borehole being drilled;
sensors in said borehole being drilled for detecting vectors of gravity and of the generated magnetic field; and
a controller responsive to the generated magnetic field and the measured magnetic field vectors to control the direction of further drilling. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for controlling the drilling of a borehole with respect to a guide borehole, comprising:
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drilling a guide borehole;
obtaining a survey of said guide borehole to determine its path;
inserting in said guide borehole a coil assembly including a tubular, nonmagnetic core and at least one winding wound externally on said core in a plane parallel to the longitudinal axis of the core;
energizing said core with an excitation current to produce a corresponding magnetic field;
partially drilling with a drilling tool a second borehole near said guide borehole;
detecting the produced magnetic field at the drill head of the drilling tool;
iteratively comparing the detected magnetic field with theoretical magnetic fields calculated from said current and the location of said coil assembly to determine the location of the drill head with respect to said coil assembly; and
guiding the further drilling of said second borehole in accordance with the calculated location of the drill head.
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Specification