基于等值反磁通瞬变电磁法的岩溶探测分析

An analysis of karst exploration based on opposing coils transient electromagnetic method

瞬变电磁法早期二次场是浅层地质信息的反应,一次场关断产生的自感电场会与早期二次场进行叠加形成一个浅层盲区,造成探测结果不能真实反映浅层地层信息。对早期纯二次场的探测能够从根本上消除浅层盲区。文中首先介绍了等值反磁通瞬变电磁法的线圈装置,通过零磁通面积感应电压规律的分析,对该方法如何实现早期二次场采集进行了说明。以某水电站公路边坡岩溶探测为研究背景,通过对测试数据的反演结果进行分析,得到了不同深度地层电阻率信息,圈定了岩溶的空间位置分布。事实证明等值反磁通瞬变电磁法能有效避免一次场关断对二次场的影响,基本消除了浅层盲区,实现了浅层地层的准确探测。

The early quadratic field of the transient electromagnetic method is the response of shallow geological information. The selfinduction electric field generated by a shut off of primary field is superimposed with the early secondary field,which causes the results that the detection result can＇t reflect the shallow stratum information and form a shallow blind area,and that the detection of early pure secondary field can fundamentally eliminate shallow blind spots. This paper first introduces the coil device of the opposing coils transient electromagnetic method,illustrates the method of the early secondary field acquisition,and meanwhile briefly describes the zero flux surface and the analysis of the regularity of induced voltage. Taking the karst exploration of highway slope of a hydropower station as the research background,the authors obtained the apparent resistivity information of strata of different depths,and delineated the spatial distribution of karst based on the analysis of the inversion results of the test data. It is proved that the opposing coils transient electromagnetic method can effectively avoid the impact of primary field shutdown on the secondary field,basically eliminates the shallow blind zone,and realizes the accurate exploration of the shallow stratum.