长导线源瞬变电磁响应中激电效应的影响特征

Influence of IP effect on grounded-wire TEM response

长导线源瞬变电磁实际测量时,经常观测到二次场衰减曲线的“符号反转”现象,这主要由于激发极化效应(IP效应)引起,这种现象对瞬变电磁响应数据和解释的可靠性产生影响。为了探讨IP效应对瞬变电磁的影响规律,首先在均匀半空间中研究激电效应影响规律,得出影响瞬变电磁响应的主要参数,然后引入相对误差表征极化效应的影响程度,来研究典型层状模型中极化层厚度和极化层埋深对瞬变电磁响应影响规律,最后以某石墨矿区地质物性参数为基础,对受激电效应影响的长导线源瞬变电磁数据解释,研究激电效应对实测数据的影响。通过研究得出结论:在均匀半空间模型中,零频电阻率和极化率对瞬变电磁响应的影响较大;对层状模型和实测数据的研究发现,当极化层的厚度、埋深和电阻率在一定范围内影响最大,而且即使实测石墨矿的极化率远小于这里采用的极化率值,但造成的影响不可忽略,因此表明激电效应对瞬变电磁的影响是复杂的。

The"sign reversal"phenomenon of the secondary field decay curve is often observed when the Grounded-wire transient electromagnetic measurement,which is mainly due to the induced polarization effect(IP effect).The IP effect has an effect on the reliability of transient electromagnetic response data and interpretation.In order to study the effect of induced polarization on the transient electromagnetic,in this paper,firstly,the influence parameters of the device parameters and formation parameters are studied in a uniform half-space,and the main parameters affecting the transient electromagnetic response are obtained.And then the relative error is introduced to indicate the degree of influence of the polarization effect.The effect of variation in the thickness of the polarization layer and the depth of the buried layer on the transient electromagnetic response in a typical layered model is studied.Finally,based on the geophysical parameters of a graphite mine area,the Grounded-wire transient electromagnetic data affected by the IP effects are interpreted to study the effect of the induced electric effect on the measured data.Through the study,it is concluded that resistivity and polarizability have a greater influence on the transient electromagnetic response in the polarizable free half-space model;the study of the layered model and measured data indicates that the polarizability of the measured graphite ore is much smaller than the polarizability value used in this paper,however,the impact on measured data cannot be ignored.It shows that the effect of the IP effect on transient electromagnetics is complex.