Patent attributes
A signaling apparatus comprises a magnet and a shield moveable relative to the magnet. The shield is moveable relative to the magnet between a first position in which the magnet is relatively exposed and a second position in which the magnet is relatively shielded. The apparatus can include a synchronization signal source, a downhole sensor signal source, and/or means for modulating the magnetic field in response to the signal from any source. A method of using the signaling apparatus to locate a bottomhole assembly includes moving the shield so as to modulate the magnetic field created by the magnet, sensing the modulation of the magnetic field, and determining the location of the bottomhole assembly using the information collected. The BHA can be located using phase shift or amplitude measurements. Receivers detecting the modulated magnetic field can be at or below the earth's surface.
