Patent ID: 7370709
Filing Date: 2008-05-13
Classification: G01V

Abstract:
1. A magnetic-field shielding apparatus for use in a subterranean well having a wellbore extending through a subterranean formation, the wellbore containing a downhole device having an interior passageway extending therethrough, the downhole device producing a magnetic field in the interior passageway, the magnetic-field shielding apparatus comprising: a mandrel defining an apparatus interior passageway of a size to allow a downhole tool to pass longitudinally through the apparatus interior passageway; the apparatus of a size to fit into the interior passageway of the downhole device; and a magnetic-field shield assembly on the mandrel, the assembly having at least two radially overlapping layers of material, at least one of the layers being a magnetic material and at least one of the layers being a non-magnetic material, the shield assembly operable to dampen the magnetic field produced by the downhole device, thereby capable of shielding a downhole tool located in the apparatus interior passageway from the magnetic field.