中心回线方式瞬变电磁测深虚拟全区视电阻率和一维反演方法

Pseudo-full-region apparent resistivity and its one-dimensional inversion for center-loop-line configuration TEM data

1. 中国地质大学,湖北武汉430074;2. 中国石油天然气集团公司物探重点实验室江汉石油学院研究室,湖北荆州434102

1. China University of Geosciences, Wuhan 430074,China;2. Key Lab. of Geophysical Prospecting, CNPC, Jianghan Petroleum University, Jingzhou 434102,China

根据半无限均匀介质空间中场的表达式,分析了一维层状介质情况下的中心回线方式瞬变电磁测深法的全区视电阻率定义的基本性质,并讨论了求解方法。特别地,引入了基于感应电动势的“虚拟全区视电阻率”概念,从而解决了全区视电阻率解的唯一性和存在性等问题。“虚拟全区视电阻率”能连续和直观地反映地下一维电性层电性垂向变化特征,对瞬变电磁测深资料的定性解释具有重要的意义,同时也为一维反演 (构制初始模型和确立目标函数)奠定了基础。模型试验表明,根据“虚拟全区视电阻率”曲线,采用一维“正演修正法”进行反演是一种可行的方法。

On the basis of field expression in half infinite homogeneous medium space, this paper discusses the basic properties of full region apparent resistivity for data acquired with center loop line transient electromagnetic method and their solving method. The concept of pseudo full region apparent resistivity is introduced which is useful in solving the existence and uniqueness of full region apparent resistivity solution. The pseudo full region apparent resistivity is able to reveal the vertical variations of electrical property continuously and intuitively in underground one dimensional conductive layers. It plays an important role in qualitative interpretation of transient electromagnetic data and lays foundations for one dimensional inversion (to construct initial model and objective function). A new one dimensional TEM inversion method called forward modification is also introduced in the paper. Model experiments show that results from the method on pseudo full region apparent resistivity data is accurate and stable.