典型地电异常的三维地—井瞬变电磁响应研究

发布时间：2018-02-23 11:40

本文关键词： 典型地电异常体地—井瞬变电磁法时域有限差分数值模拟响应规律　出处：《东华理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：地—井瞬变电磁法(Down-hole TEM)是指将接收探头放在钻井中观测瞬变电磁场响应的一种地球物理深部找矿方法。由于接收探头处于地面以下,直接屏蔽了部分的地面电磁噪声,与地面瞬变电磁法相比,具有二次场不易受到地表低阻层干扰,接收探头距离深部目标体近,纵向分辨率高等优势,从而获得比地面瞬变电磁法更强的探测能力。地—井瞬变电磁法能够用于确定异常体的埋深位置、组合情况以及追踪异常体的延伸方向,具有良好的“旁视”能力。因此被广泛应用于区域地质深部调查和寻找井旁隐伏盲矿。但是地—井瞬变电磁法的正演理论研究相对滞后,因此本文在前人研究总结的基础上,通过地—井观测模式下的数值模拟方法对典型地电异常体的瞬变电磁响应进行了分析研究。本文运用Wang和Hohmann的经典时域有限差分算法,从Maxwell方程组旋度方程出发,采用稳定收敛的Dufort-Frankel法对瞬变电磁总场和二次场扩散方程进行离散,使用非均匀网格剖分技术对模型进行剖分。在吸收边界条件研究方面,以完全匹配层吸收边界条件为基础,为了满足扩散方程中低频电磁波传播的特点,修改了CFS-PML边界条件。与传统的第一类Dirichlet边界条件应用效果进行对比,结果显示出CFS-PML边界条件能更好的满足低频电磁场的扩散要求。通过吸取前人研究总结的经验,结合实际情况下局部矿体往往由多个导体组合在一起的现象,构建典型地电异常体的地质—地球物理模型,对垂直接触带、背斜、向斜、地垒、地堑、倾斜板状体、立方体模型的异常响应特征进行了全面深入的剖析,并将地—井观测系统下瞬变电磁场随时间和深度变化的扩散规律进行重点研究。结果表明:异常响应主要受到目标体尺寸大小、埋深深度、赋存条件、地电特性、地质构造、与场源耦合关系等因素综合影响。最后将影响地—井瞬变电磁响应的因素进行总结归纳,为今后的地—井TEM响应分析和数据解释提供参考。
[Abstract]:The earth-well transient electromagnetic method (Down-hole TEM) is a geophysical deep prospecting method in which the receiver probe is placed in a well to observe the transient electromagnetic field response. Since the receiving probe is below the surface, it directly shields part of the surface electromagnetic noise. Compared with the ground transient electromagnetic method, the secondary field is difficult to be interfered with by the surface low resistance layer, the receiving probe is close to the deep object, and the longitudinal resolution is high. The ground well transient electromagnetic method can be used to determine the buried depth of the anomalous body, the combination of the anomalous body and the tracing of the extended direction of the abnormal body, so as to obtain a better detection capability than the surface transient electromagnetic method. Because of its good side-view ability, it has been widely used in regional geological deep investigation and searching for hidden blind deposits near wells. However, the forward modeling theory of ground-well transient electromagnetic method is lagging behind, so this paper is based on the previous studies. The transient electromagnetic response of a typical geoelectric anomaly is analyzed by means of numerical simulation in the geoelectric observation mode. In this paper, the classical finite-difference time-domain (FDTD) algorithm of Wang and Hohmann is used to analyze the transient electromagnetic response of a typical geoelectric anomaly. Based on the curl equation of Maxwell equations, The diffusion equations of transient electromagnetic total field and secondary field are discretized by Dufort-Frankel method with stable convergence, and the model is subdivided by non-uniform mesh generation technique. In the study of absorbing boundary conditions, the perfectly matched layer absorbing boundary condition is used as the basis. In order to satisfy the characteristics of low frequency electromagnetic wave propagation in diffusion equation, the CFS-PML boundary condition is modified. The results show that the CFS-PML boundary condition can better meet the diffusion requirements of low frequency electromagnetic fields. By absorbing the experience of previous studies and combining with the actual situation, the local orebodies are often combined by multiple conductors. The geo-geophysical model of typical geoelectric anomaly is constructed, and the abnormal response characteristics of vertical contact zone, anticline, syncline, barrier, graben, inclined plate body and cube model are thoroughly analyzed. The diffusion law of transient electromagnetic field with time and depth under the geo- well observation system is studied emphatically. The results show that the abnormal response is mainly affected by the size of the object, the depth of buried depth, the conditions of occurrence, the geoelectric characteristics, and the geological structure. Finally, the factors affecting the ground well transient electromagnetic response are summarized and summarized to provide a reference for the future ground well TEM response analysis and data interpretation.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.325

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