电性源瞬变电磁B场全程视电阻率计算

Calculation of all-time apparent resistivity for B field due to electrical source TEM

在传统电性源瞬变电磁资料解释中,常常采用Bz/T求取视电阻率值,由此带来Bz/T计算全程视电阻率多解性.而Bz随电阻率变化是单值函数,由Bz计算全程视电阻率具有减少多解性的优势.为了研究接地源瞬变电磁B场全程视电阻率,文中首先研究了接地源瞬变电磁法Bz和Bz/T响应值随电阻率的变化特性,然后设计不同的地电模型,采用二分搜索算法对B场全程视电阻率进行计算,结果表明全程视电阻率对电性目标体分辨率高,分层能力强,能较好地反映地电断面的信息;另外,全程视电阻率仅与地层的电性结构有关,与收发距无关,便于野外进行接地源瞬变电磁近源测量.在实际应用中,通过把观测的二次感应电压转换成磁场微分数据,再对磁场微分数据进行积分,求取B场数据,并进而求取视电阻率,取得了较好的应用效果.

TraditionallyBz/T is used to obtain the apparent resistivity values in the data interpretation of grounded-wire source transient electromagnetic,which lead to the problem of multiple solutions.This problem can be solved by using Bz,because the Bz with resistivity change is a single-valued function.In order to study the all-time apparent resistivity of the grounded-wire source transient electromagnetic based on B filed,the relationship between Bz orBz/T response and resistivity is analysis firstly,then all-time apparent resistivity is calculated using method of dichotomy for different geoelectric models.It is concluded that all-time apparent resistivity has high resolution reflects and only responds to the geoelectric structure well.all-time apparent resistivity has nothing to do with the offset.So,it is easy for us to observed the near soure data.Field data,the induced voltage is transformed to the B field data using the integral,then,calculated the all-time apparent resistivity is up to the real geoelectric structure.