Method of Magnetic Interference Correction in Survey with Magnetic MWD

In order to improve accuracy of well trajectory measured by MWD,magnetic interference correction was studied.Inclination angle,tool-face and azimuth angle were worked out when surveying with magnetic MWD.Cross-axial magnetic interference originating from magnetic hot spots in the NMDC was corrected by rotating drillstring 360° and analyzing cross-axial magnetometer data.Axial magnetic interference originates from the magnetization of ferromagnetic portions of the drill string was corrected by loop iteration method.A series of conclusions were reached by a group of simulation data including survey data,magnetic interference data and geomagnetic parameters:the error of measured azimuth was larger when inclination approaches 90° or azimuth approaches 90°,270°;the error of measured azimuth was smaller when inclination approaches 0° or azimuth approaches 0°,180°;the measured azimuth was smaller than true azimuth when true azimuth was between 0° and 180°;the measured azimuth was larger than true azimuth when true azimuth was between 180° and 360°;the effect of correcting axial magnetic interference was poorer when trajectory approaches horizontal west or east and the correcting algorithm was stable.