Patent ID: 7413011

Claim:
A system for locating magnetic permeability anomalies in wellhole piping and tubing installed within a borehole, said system comprising: a source of light located outside a well; a first optical fiber operable to extend into a wellhole connected to said source of light; an optical depolarizer in line with the said first optical fiber and located between the well hole and the source of light; an optical coupler or optical circulator in line with the said first optical fiber located between the optical polarizer and the well hole; a second optical fiber connected to the said optical coupler or optical circulator; a signal detector and analyzer connected to said second optical fiber; and a sensor assembly connected downhole to said first optical fiber, including: magnets oriented to create a magnetic field within the vicinity of said sensor, an optical collimator attached to said first optical fiber, a Faraday crystal positioned downstream of said optical collimator, an optical reflecting device positioned downstream of said Faraday crystal capable for redirecting the light back through said first optical fiber and, ultimately, to the said signal detector and analyzer located at the well surface, wherein said sensor assembly is operable to experience light insertion losses as a function of perturbations in magnetic fields near said sensor resulting from the masses of downhole tubing adjacent to the sensor assembly.