井眼轨迹随钻测量中的测斜仪器不对中随机误差分析

Stochastic error analysis of misalignment between axis of inclinometer and trajectory in process of measuring while drilling

为了更加准确地描述随钻测量时产生的井眼轨迹误差,利用误差分析方法对随钻测量时测量仪器与井眼轴线不重合所产生的误差进行了分析,并采用拉格朗日插值进行了计算。结果表明,这种不对中所引起的测量误差属于随机误差的范畴,该误差对井斜和方位测量结果的作用是相同的,且服从均匀分布。算例分析表明,这种随机误差相对于系统误差所造成的井眼位置的不确定范围要小得多。测点处的随机误差椭球的中心与测点之间的距离很近,但是,随着钻头尺寸与钻铤尺寸差别的增大,此距离增大,并且椭球的3个半轴也呈现相同的变化趋势。

In order to describe the trajectory error derived from measurement while drilling more accurately, the error caused by misalignment between axis of inclinometer and borehole axis was analyzed by error analysis theory and calculated by Lagrange interpolation method. The results indicate that the misalignment error should be included into the scope of stochastic error. According to the characteristics of this kind of error item, it will take equal effect on inclination and azimuth of the survey results. And the distribution feature of this stochastic error belongs to the uniform distribution. Through analysis and comparison, this stochastic error produces much less uncertainty compared with systematic error. The center of stochastic error ellipsoid at a survey station is close to this survey station. With the increase of the gap, the distance between the center of stochastic error ellipsoid and the corresponding survey station increases too. The dimension of ellipsoid also takes the same variation tendency.