双回线瞬变电磁法全空间三维正演方法与响应特征  

3D forward modeling and response characteristics of two-loop TEM in whole space

作　　者：李飞[1] 王圣龙 郑贵强[1] LI Fei;WANG ShengLong;ZHENG GuiQiang(Key Laboratory of Mine Disaster Prevention and Control,North China Institute of Science and Technology,Langfang 065201,China;China Coal Technology and Engineering Group Chongqing Research Institute,Chongqing 400039,China)

机构地区：[1]华北科技学院,河北省矿井灾害防治重点实验室,廊坊065201 [2]中煤科工集团重庆研究院有限公司,重庆400039

出　　处：《地球物理学进展》2022年第3期1047-1059,共13页Progress in Geophysics

基　　金：河北省自然科学基金(D2019508160,D2019508167);国家重点研发计划课题(2017YFC0804105)联合资助。

摘　　要：瞬变电磁法是矿井巷道和隧道超前探测最常用和有效的方法之一,常规方法采用多匝方形回线源,存在易受干扰和双向探测等问题.双回线方法采用8字形回线源,在解决以上问题等方面有优势.首先,基于场的叠加原理构建了双回线初始场源,在常规瞬变电磁三维有限差分正演算法基础上建立了双回线瞬变电磁三维正演方法.通过与数字滤波解的对比,验证了算法的可靠性.然后,建立了全空间均匀介质模型、全空间含低阻层模型和全空间含低阻三维块体模型,分别进行了双回线方法和常规方法的正演计算和对比.结果表明:双回线方法在围岩和低阻体中感应产生双涡旋电流场;双回线方法观测值(磁感应强度随时间变化率)的水平分量相对强于垂直分量,且更均匀,所以观测水平分量更有优势,但弱于常规方法,强度相差在两个数量级以内;异常体位于双回线上方和下方时观测值的水平分量方向相反,具有全空间可分性,但曲线形态比常规方法复杂,存在变号现象.最后,对变号的原因和与异常体的关系进行了探讨,发现变号现象是低阻体涡旋电流场和围岩涡旋电流场共同作用的结果,根据变号信息可以估计异常体的位置和尺寸.双回线方法可以作为常规方法的有效补充,提高瞬变电磁法全空间探测精度.Transient Electromagnetic Method(TEM)is one of the most widely used and effective methods for roadway and tunnel advanced detection.The conventional method uses one-loop source,which is susceptible to interference and has bidirectional detection problem.Two-loop method is expected to solve the above problems.Firstly,the two-loop source initial field is constructed based on the superposition principle,and the three-dimensional forward algorithm is established.Compared with the digital filter solution,the algorithm is verified.Then,the whole space homogeneous medium model,the whole space model with low resistivity layer and the whole space model with low resistivity three-dimensional block are established.Forward calculation and comparison between two-loop method and one-loop method are carried out.Results show that:two-loop method induces double eddy current field in surrounding rock and low resistance body;both the horizontal and vertical components of two-loop method are weaker than one-loop method,the horizontal component of two-loop method is stronger than the vertical component,and more uniform,so the horizontal component is more advantageous;two-loop method can separate the anomaly body above and below the tunnel,the horizontal component of two-loop method has the sign changing phenomenon.Finally,the cause of sign changing and the relationship between sign changing and abnormal body are discussed.It is found that sign changing is the result of the interaction of vortex current field of low resistivity body and surrounding rock.According to sign changing information,the position and size of abnormal body can be estimated.Two-loop method can be used as an effective supplement to one-loop method to improve detection accuracy in whole space.

关 键 词：双回线 8字形回线 瞬变电磁法 全空间 三维正演 响应特征 

分 类 号：P631[天文地球—地质矿产勘探]