Calculation and Correction of Azimuth Errors Based on Finite Element Analysis
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摘要:
为了满足定向井磁方位的高精度需求,需要准确计算方位角测量误差和分析误差来源。采用有限元分析软件,模拟了钻具在地磁场中产生的干扰磁场的变化情况。通过钻杆内部三轴磁感应强度得出方位角误差的测量值,与钻杆真实方位对比得到了方位角误差。通过控制钻杆方位角、井斜角、底部钻具组合、无磁钻铤长度、外部磁场的大小和方向等因素,来观测、分析了方位角误差的变化规律。模拟试验得出,方位角误差在钻杆的南北方向上最小,在钻杆的东西方向上最大,并随着井斜角增大而增大,这种变化呈现出正弦的变化规律;经度、纬度也会对方位角的变化产生影响,方位角误差大体上随着维度增加而增大,主要取决于当地的总磁场和磁倾角大小。研究结果表明,方位角误差与测斜数据、底部钻具组合、经度、纬度和无磁钻铤长度有密切关系,可以通过有限元模拟准确估算出不同情况下方位角误差的大小,对方位角误差进行修正。模拟结果可为工程应用中无磁钻铤、底部钻具组合的选取和方位角误差修正提供参考数据和理论依据。
Abstract:The high-precision magnetic azimuth of directional wells requires the accurate calculation of azimuth measurement errors and analysis of error sources. In this study, the finite element analysis (FEA) software was used to simulate the change in the interference magnetic field generated by the drill tool in the geomagnetic field. The measured azimuth error was obtained through the triaxial magnetic induction intensity inside the drill pipe and was compared with the real azimuth of the drill pipe to get the azimuth error. Then, the variation laws of azimuth errors was observed and analyzed by controlling factors including the azimuth of the drill pipe, deviation angles, bottom hole assembly (BHA), non-magnetic drill collar length, and the size and direction of the external magnetic field. The simulation test showed that the azimuth error was the smallest in the north-south direction and the largest in the east-west direction of the drill pipe, and it increased with the rise in the deviation angles, which presented a sinusoidal variation law. Longitude and latitude would also affect the change in azimuth, and the azimuth error grew with the increase in dimensions in general and mainly depended on the local total magnetic field and magnetic inclination. The research results indicate that the azimuth error closely correlates with the inclinometer data, BHA, longitude, latitude, and the non-magnetic drill collar length, and it can be accurately estimated by finite element simulation under different conditions and then be corrected accordingly. The simulations can provide a reference and theoretical basis for the selection of the non-magnetic drill collar and BHA, and the correction of azimuth errors in engineering applications.
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表 1 方位角误差模型采用的钻具数据
Table 1 Data of drill tools used in the azimuth error model
钻具或仪器 长度/mm 外径/mm PDC钻头 280 215.9 旋转导向工具 7 520 171.4 BCPM测井工具 4 940 171.4 集成井下测量仪 6 660 171.4 无磁钻铤 9 270 171.4 浮阀 680 165.1 加重钻杆 9 410 127.0 钻杆 9 410 127.0 表 2 4种典型井底钻具组合对比
Table 2 Comparison of four typical BHAs
底部钻具组合 上部磁极强度/
μWb下部磁极强度/
μWb无磁钻铤距钻头的距离/m 钻头和稳定器 900 90 2 钻头和钻铤 900 300 10 钻头和螺杆钻具 900 1 000 10 钻头和旋转导向 900 3 000 10 -
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