Correction Methods for Axial Magnetic Interference of the Magnetic Inclinometer while Drilling

When the magnetic inclinometeris subjected to axial magnetic interference while drilling,the measured azimuth is inaccurate.To deal with this problem,the measurement principle of magnetic inclinometer while drilling was introduced.Then,the principle and iterative calculation process of two indirect magnetic interference correction methods(i.e.,the Russell method and the short drill collar measurement correction method)were analyzed,and two direct magnetic interference correction methods(i.e.,vector sum method and drilling tool section method)were proposed.And finally,numerical simulations were performed for these four methods.Results indicated that direct correction methods are simple,but their calculation is limited in several ways.Indirect correction methods are complicated,but their calculation accuracy is higher.Meanwhile,the azimuth deviation increases with the increase of the interference magnetic fields while the other borehole parameters are unchanged.When the axial interference magnetic field is fixed,the azimuth deviation increases when the inclination angle increases.When the inclination angle is the same,the azimuth angle increases first and then decreases in the range of 0°-360°,revealing the symmetry.When the well trajectory is close to horizontal EW orientation,the correction effect of axial magnetic interference is the worst.All the four correction methods can be better applied in field. They can decrease the influence of axial magnetic interference on the measurement accuracy of the azimuth angle and reduce the service length of non-magnetic drill collar.