Method of Magnetic Interference Correction in Survey with Magnetic MWD
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摘要: 为提高磁力随钻测量的井眼轨迹精度，研究了随钻测量磁干扰校正方法。利用随钻测量参数，计算井斜角、工具面角和方位角；采取360°旋转钻柱记录、分析径向磁力计读数的方法，纠正磁热点引起的径向磁干扰；采用循环迭代的方法，纠正钻柱磁化引起的轴向磁干扰。通过仿真测量参数、磁干扰数据和地磁参数，应用磁干扰校正方法计算得到校正方位角，并与实测方位角、真实方位角进行了对比，结果发现，在其他井眼参数保持不变的条件下，井斜角接近90°或方位角接近90°、270°时，实测方位角误差变大；井斜角接近0°或方位角接近0°、180°时，实测方位角误差变小；真实方位角为0°~180°时，实测方位角比真实方位角小，真实方位角为180°~360°时，实测方位角比真实方位角大；井眼轨迹接近水平东或水平西方向时，轴向磁干扰的校正效果最差。磁干扰校正方法能够提高方位角测量精度，减少无磁钻铤长度。Abstract: 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.
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