均匀半空间脉冲电流的TEM响应正演计算研究  

Study on the TEM response forward calculation of uniform half-space pulse current

作　　者：李奇霖 康慧敏 王光杰[1,2,3] 于丽君 朱建峰 王若 张永超[6] 曹文静 LI QiLin;KANG HuiMin;WANG GuangJie;YU LiJun;ZHU JianFeng;WANG Ruo;ZHANG YongChao;CAO WenJing(Institute of Geology and Geophysics,Chinese Academy of Sciences,Institute of Earth Science,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China;Key Laboratory of Shale Gas and Geoengineering,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Xiamen University,Xiamen 361005,China;The Aerospace Information Research Institute,Chinese Academy of Sciences,Beijing 100094,China;Mine Safety Technology Branch,China Coal Research Institute,Beijing 100013,China)

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院地球科学研究院,北京100029 [2]中国科学院大学,北京100049 [3]中国科学院页岩气与地质工程重点实验室,北京100029 [4]厦门大学,厦门361005 [5]中国科学院空天信息创新研究院,北京100094 [6]煤炭科学技术研究院有限公司安全分院,北京100013

出　　处：《地球物理学进展》2023年第3期1152-1160,共9页Progress in Geophysics

基　　金：国家重点研发计划(2020YFC1521900)资助。

摘　　要：瞬变电磁法因其对低阻体反应灵敏、工作效率高等优点成为应用广泛的地球物理方法.而信号强度是制约瞬变电磁发展的重要因素.国内外学者对提高发射功率增强信号强度研究较多,但从脉冲宽度角度研究信号强度的参考文献较少.本文提出一种在总功率不变的条件下通过减小脉冲宽度增大发射电流来增强场源强度的方案.首先通过计算均匀半空间正、负阶跃电流激励的dB_(z)/dt响应,根据电磁场叠加原理推导出不同脉冲宽度瞬变电磁响应的一般表达式.其次针对均匀半空间地层,研究了不同收发距、不同电阻率、不同电流脉冲宽度对TEM二次场响应特征影响的变化规律.最后从能量角度分析了不同占空比的瞬变电磁响应特征.结果表明:均匀半空间地层模型中,电流一定时,脉冲宽度越大,释放的能量越大,dB_(z)/dt值越大;发射机总功率不变时,利用电容器储能技术适当减小脉冲宽度和占空比有利于提高场源信号强度,但占空比过小则不利于大深度TEM探测.Transient Electromagnetic Method(TEM)has become a widely used geophysical,prospecting method because of its sensitive response and high efficiency to low resistivity targets.The noise suppression technology is an important factor restricting the development of TEM.In response to this problem,many scholars have been carried out at home and abroad,mainly to enhance the signal strength by increasing the transmit power.There are fewer references to the signal strength from the hardware.On the basis of previous researches,this paper proposes a scheme to enhance the intensity of the field source by reducing the pulse width and increasing the emission current by using the capacitor energy storage technology under the condition of the same total power.Firstly,by calculating dB_(z)/dt response of positive and negative step current excitation in uniform half space,according to the_superposition principle of electromagnetic fields,the general expressions of TEM response under different pulse widths are derived.Secondly,according to the formation of uniform halfspace,the effects of different transmitting and receiving distances,different resistivities and different current pulse widths on the response characteristics are studied.Finally,the TEM response characteristics of different duty cycles are analyzed from the transmitter energy point of view.The results show that,in the uniform half-space formation model,when the current is constant,the greater the pulse width and the greater the dB_(z)/dt value;When the transmitter energy is constant,the larger the pulse width is,the smaller the dB_(z)/dt value is.Small duty cycle is beneficial to reflect shallow geological information.Reducing the duty-taking ratio can improve the signal strength,which is beneficial to the bathymetry,and too small is not conducive to the actual bathymetric.It can provide theoretical reference for the development of transient electromagnetic transmitter.

关 键 词：瞬变电磁 脉冲宽度 占空比 信号强度 考古勘探 正演 

分 类 号：P631[天文地球—地质矿产勘探]