Importance

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Abstract

A method and apparatus for determining the distance and direction to a borehole containing ferromagnetic material includes placing a sensor package in a second nearby borehole and measuring three vector components of the static magnetic field perturbations of the earth's magnetic field caused by the ferromagnetic material. The sensor package is moved within the second borehole to obtain a plurality of magnetic field measurements, and the measured components are then projected onto a system of fixed coordinates whose orientation in space is known. The relative direction from the second borehole to the first is determined from the vector components, and the magnitude of the resultant in the direction of the first borehole is then determined from the fixed coordinate system. In a modification, the sensor package includes two spaced magnetometers for measuring vector components of the magnetic field perturbations. The measured components are subtracted to obtain a difference value which represents the perturbations in the total magnetic field.

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First Claim