井下瞬变电磁探测信号基线漂移校正方法

Baseline wander correction method for downhole transient electromagnetic exploration signals

利用涡流的时域扩散特性,瞬变电磁技术已广泛应用于井下探测领域。然而,测试过程中井下温度的变化会使探头的磁导率发生变化,导致测试曲线的基线产生漂移,严重影响套管损伤检测的性能。针对这一问题,提出基于经验模态分解的井下瞬变电磁探测信号基线漂移校正方法。通过对瞬变电磁信号进行分解,结合信号的频谱特性,对含有基线漂移的本征模态函数进行滤波处理,并将滤波后的结果作为测试曲线的重构信号,进而实现瞬变信号的基线漂移校正。现场实验结果表明,该方法能够有效地校正测试曲线的基线漂移,提高反演解释的精度。

By virtue of the time-domain diffusion characteristic of the eddy current,the transient electromagnetic(TEM)technology has been widely used in the field of downhole exploration.However,in the process of testing,the magnetic conductivity of the probe changes as the downhole temperature changes,which leads to the baseline wander of the test curve,and seriously affects the performance of casing damage inspection.In view of this,a method of empirical mode decomposition(EMD)based baseline wander correction of downhole TEM exploration signals is proposed.On the basis of decomposing the TEM signals and combining their spectrum characteristics,the intrinsic mode function(IMF)with baseline wander is subjected to filtering processing.The results of filtering processing are taken as the reconstructed signals of the test curve to correct the baseline wander of the transient signals.A field experiment was conducted.The results show the proposed method can effectively correct the baseline wander of the test curve and improve the accuracy of the data inversion.