摘要
巷−孔瞬变电磁法在存在明显电导率各向异性的勘探区会产生较大的解释误差。基于时域有限差分算法,通过引入电导率各向异性张量构建控制方程、将矩形回线源电流密度加入Maxwell方程安培环路定理实现任意电流源的加载,以差分代替微分对控制方程进行离散,实现巷−孔瞬变电磁三维模型正演计算。在与解析解对比验证算法计算精度的基础上,构建全空间模型、层状模型和三维块状模型进行正演并分析电导率各向异性对巷−孔瞬变电磁三分量响应的影响程度与方式。结果表明:垂直轴电导率对巷−孔瞬变电磁三分量响应基本没有影响,水平轴电导率对巷−孔瞬变电磁三分量响应影响较大,其中,∂Bx/∂t响应主要受y轴电导率影响,∂By/∂t响应主要受x轴电导率影响;通过三分量响应的形态和幅值的相互关系可以辨别各向异性介质所在方位及主轴电导率方向;当异常体所处全空间介质为电导率各向异性时,异常体产生的异常响应会被全空间介质电导率各向异性产生的异常响应所淹没。电导率轴向各向异性特征在巷−孔瞬变电磁法解释过程中不可忽略,研究成果为巷−孔瞬变电磁法各向异性解释提供指导,也为各向异性反演提供参考。
Large interpretation errors may exist in exploration areas with obvious conductivity anisotropy when applying tunnel-hole transient electromagnetic method.In this paper,the control equation is built by introducing the conductivity anisotropy tensor,which allows the current density of the rectangular loop source to be added into the Maxwell equation Ampere loop theorem based on the finite difference time domain(FDTD)algorithm in order to realize the loading of any current source.The control equation is discretized by the difference instead of the differential to realize the forward calculation of the tunnel-hole transient electromagnetic 3D model.Forward modeling is carried out for a full-space model,a layered model and a 3D block model based on the accuracy comparison between the analytical and numerical solution.Then the influence and the mode of the conductivity anisotropy on the three-component transient electromagnetic responses of the tunnel-hole is analyzed.The results show that the vertical axis conductivity has little effect on the tunnel-hole transient electromagnetic three-component responses,and the horizontal axis conductivity has a great influence on it.The∂Bx/∂t response is mainly influenced by the y-axis conductivity,while the∂By/∂t response is mainly influenced by the conductivity of the x-axis.The orientation of the anisotropic medium and the direction of the main axial conductivity can be identified through the relationship between the shape and amplitude of the three-component responses.When the all-space medium where the anomalous body is located is anisotropic in conductivity,the anomalous response generated from the anomalous body will be overwhelmed by the anomalous response generated by the anisotropic conductivity of the all-space medium.Thus we lead the conclusion that the characteristics of conductivity axial anisotropy cannot be ignored in the process of tunnel-hole transient electromagnetic interpretation.This research could provide guidance for the anisotropic interpretation
作者
郭建磊
高小伟
侯彦威
GUO Jianlei;GAO Xiaowei;HOU Yanwei(Xi’an Research Institute Co.Ltd.,China Coal Technology and Engineering Group Corp.,Xi’an 710077,China)
出处
《煤田地质与勘探》
CAS
CSCD
北大核心
2022年第7期52-62,共11页
Coal Geology & Exploration
基金
陕西省自然科学基础研究计划项目青年基金项目(2020JQ-994)
中煤科工集团西安研究院有限公司科技创新项目(2019XAYMS30)。
关键词
各向异性
电导率
巷−孔瞬变电磁法
时域有限差分
三分量
正演计算
anisotropy
conductivity
tunnel-hole transient electromagnetic method
finite difference time domain
three-component
advanced detection
