地形对回线源瞬变电磁法探测影响的三维正演研究  

Three dimensional numerical simulation of transient electromagnetic method in undulating terrain

作　　者：马炳镇 郭建磊 MA Bingzhen;GUO Jianlei(Xi'an Research Institute, China Coal Technology and Engineering Group,Xi'an 710077,China)

机构地区：[1]中煤科工集团西安研究院有限公司,西安710077

出　　处：《物探化探计算技术》2021年第6期734-742,共9页Computing Techniques For Geophysical and Geochemical Exploration

基　　金：中煤科工集团西安研究院有限公司科技创新项目(2019XAYMS30);陕西省自然科学基础研究计划一般项目(2020JQ-994)。

摘　　要：为研究地形对回线源瞬变电磁法探测影响特征,采用时域有限差分法进行三维数值模拟,在构建时域有限差分方程时引入了虚拟位移电流项实现源的加载,使研究回线源随地形起伏的响应特征具备了条件。模拟了水平回线源下,接收点位于山峰、沟谷地形时,H及K型层状模型的地形响应特征。结果表明,沟谷地形H及K型模型响应信号均在早期感应电动势值减弱,导致“假高阻异常”,中、晚期感应电动势值增强,导致“假低阻异常”;山峰地形模型响应特征恰好相反,以上地形影响至晚期均逐渐减小。为适应实际施工场景,进一步模拟了回线源随地形起伏时瞬变场的响应特征,模型响应表明沟谷地形导致感应电动势值增强,呈“假低阻异常”;山峰地形相应特征亦相反,至晚期地形影响均呈逐渐减弱趋势。以上正演结果与实测数据反映特征一致。In order to study the influence of terrain on the detection characteristics of loop source transient electromagnetic method,the finite difference time domain(FDTD)method is used for three-dimensional numerical simulation.The virtual displacement current term is introduced to load the source when constructing the FDTD equation,which makes it possible to study the response characteristics of loop source with terrain fluctuation.In this paper,the terrain response characteristics of H-and K-type layered models are simulated when the receiver is located in the mountain and valley terrain under the horizontal loop source.The results show that the induced electromotive force of H-type and K-type models of valley terrain decreases in the early stage,leading to"false high resistance anomaly",and the induced electromotive force increases in the middle and late stage,leading to"false low resistance anomaly";the response characteristics of mountain terrain model are just the opposite,and the influence of the above terrain gradually decreases in the late stage.In order to adapt to the actual construction scene,the response characteristics of the transient field of the loop source are further simulated when the terrain fluctuates.The model response shows that the valley terrain leads to the increase of the induced electromotive force value,showing a"false low resistance anomaly";the corresponding characteristics of the mountain terrain are also on the contrary,and the influence of the terrain gradually weakens in the late stage.The above forward results are consistent with the measured data.

关 键 词：瞬变电磁法 三维正演 时域有限差分 地形影响 

分 类 号：P631.3[天文地球—地质矿产勘探]