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...http://www.google.fr/patents/US4933640?utm_source=gb-gplus-shareBrevet US4933640 - Apparatus for locating an elongated conductive body by electromagnetic measurement while drilling
Apparatus for locating an elongated conductive body by electromagnetic ...
