DETERMINATION OF MAGNETIC INTERFERENCE IN A BOREHOLE

摘要

S P E C I F I C A T I O N "Determination of Magnetic Interference in a Borehole" In order to determine the magnetic interference within a non-magnetic drill collar disposed in a drill string within a borehole due to the presence of magnetised sections of the drill string above and below the drill collar, two magnetic detectors are spaced apart along the axis of the drill collar so that each detector lies at an appropriate position on the axis of the drill collar. Magnetic measurements are then taken with the detectors while the drill collar is maintained at a common measurement location within the borehole such that each measurement is indicative of the component Bz1 or Bz2 of the magnetic field along the axis of the drill collar at a respective position corresponding to the position of the associated detector in that measurement location. The magnetic interference due to the magnetised sections of the drill string above and below the drill collar is then calculated from inter alia the measurements taken by the detectors at the measurement location.