Correction programmes for magnetic survey
The correction programme corrects the inclination and azimuth values for cross-axial and axial magnetic interference of the drillstring (including magnetic hot-spots in NMDCs), bias uncertainties of the accelerometers and magnetometers of the survey tool and toolface dependent misalignment.
The method does not correct for external disturbing magnetic fields such as from nearby casings or magnetic formations. The correction method assumes a constant magnetic field strength and dip angle during a complete survey. Surveys taken during magnetically unstable periods, e.g. magnetic storms, are unreliable, as discussed previously.
Magnetic . . .