薄板状导体地-井瞬变电磁场数值模拟及晚期响应特征  

Numerical simulation and late response characteristics of surface-borehole transient electromagnetic field of thin plate

作　　者：刘祖鉴 刘诗华 马一行[2,3] 张博洋 LIU Zu-Jian;LIU Shi-Hua;MA Yi-Xing;ZHANG Bo-Yang(China Aero Geophysical Survey and Remote Sensing Center for Natural and Resources,Beijing 100083,China;Development and Research Center of China Geological Survey,Beijing 100037,China;Technical Guidance Center for Mineral Resources of Ministry of Natural Resources,Beijing 100083,China;Institute of Mechanics,Chinese Academy of Sciences,Beijing 100190,China)

机构地区：[1]中国自然资源航空物探遥感中心,北京100083 [2]中国地质调查局发展研究中心,北京100037 [3]自然资源部矿产勘查技术指导中心,北京100083 [4]中国科学院力学研究所,北京100190

出　　处：《物探与化探》2020年第3期685-690,共6页Geophysical and Geochemical Exploration

基　　金：中国地质调查局项目(DD20191011)。

摘　　要：瞬变电磁在导电板状体中的感应涡流进入晚期后涡流分布状况已经趋于稳定,并按指数规律衰减。在等效数学模型中,利用等效涡流法计算晚期瞬变电磁响应更为简便,该方法能计算1~4块任意组合体和有导电围岩或覆盖层的响应情况,具有一定的适用性。本文推导了晚期瞬变电磁等效涡流场感应电压的计算方法,通过对4种典型地电模型进行数值模拟和晚期异常特征分析,得出以下结论:①在断电延时较短时,导电体异常响应幅值较大,当钻孔从异常体中心位置穿过时,异常形态为单峰正异常响应;随着时间推移,电磁响应逐步衰减。②当钻孔位于矿体边界位置时,水平矿体产生三峰对称状异常,异常峰值为负异常;倾角为45°时,矿体异常形态出现非对称正负异常,矿体顶侧出现负异常,底侧出现正异常。③相同产状条件下,简单组合板状体异常幅值较单板状体的异常幅值增大,其异常形态符合单板状体的异常响应特征。此项研究成果对利用正演拟合完善地-井瞬变电磁法的后期解释工作以及工区布置参数的确定,如回线大小、剖面长度、发射电流大小等,具有一定的意义。After the induced eddy current in the conductive thin plate is transient,the eddy current distribution has become stable and decays exponentially.In the equivalent mathematical model,it is easier to calculate the late transient electromagnetic response by the equivalent eddy current method.This method can calculate the response of any combination of 1~4 blocks and conductive surrounding rock or cover layer,and has certain applicability.In this paper,the calculation method of late transient electromagnetic equivalent eddy current field induced voltage is deduced.By numerical simulation and typical characteristic analysis of four typical geoelectric models,some results have been obtained:①When the power-off delay is short,the amplitude of the abnormal response of the conductor is large.When the borehole passes through the center of the abnormal body,the abnormal shape is a single-peak positive abnormal response;with the elapse of time,the electromagnetic response gradually decays.②When the borehole is located at the boundary of the orebody,the horizontal orebody produces a three-peak symmetrical anomaly,and the anomalous peak value is a negative anomaly;when the inclination is 45°,the anomaly morphology of the orebody exhibits asymmetric positive and negative anomalies,and a negative anomaly appears on the top side of the orebody,with positive anomaly on the underside.③Under the same condition,the abnormal amplitude of the simple plate-shaped body is larger than that of the single plate-shaped body,and its abnormal shape conforms to the abnormal response characteristics of the single plate-shaped body.The research results have certain significance for the ground-well transient electromagnetic method to use forward fitting to improve the later interpretation work and to determine the layout parameters of the work area,such as loop size,section length,point distance,and emission current.

关 键 词：地-井瞬变电磁 等效涡流场 导电薄板 磁偶源 响应特征 

分 类 号：P631[天文地球—地质矿产勘探]