轴向各向异性地层瞬变电磁三分量响应特征  

Three-component responses of axially anisotropic formations using the transient electromagnetic method

作　　者：郭建磊 GUO Jian-Lei(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,陕西西安710077

出　　处：《物探与化探》2022年第2期362-372,382,共12页Geophysical and Geochemical Exploration

基　　金：陕西省自然科学基础研究计划项目(2020JQ-994);中煤科工集团西安研究院有限公司科技创新项目(2019XAYMS30);国家自然科学基金项目(41974162)。

摘　　要：多数地层和裂隙积水区的电导率具有各向异性特性,地层的各向异性对瞬变电磁观测会产生较大的影响,尤其是对水平分量特征更加明显。为研究轴向各向异性地层的瞬变电磁三分量响应特征,基于时域有限差分算法,引入电导率张量构建控制方程,实现电导率轴向各向异性三维瞬变电磁三分量正演。通过与各向同性半空间模型和各向异性半空间模型的一维解析结果对比,验证了算法的准确性;建立各向异性半空间模型、层状模型、含水体模型并计算其回线源瞬变电磁三分量磁场响应。结果表明:水平方向电导率各向异性对三分量磁场响应均产生较大影响,其中x轴各向异性对B y/t分量响应的影响大于B x/t,y轴各向异性对B x/t分量响应的影响大于B y/t,z轴各向异性对三分量磁场响应几乎没有影响;浅部地层的电导率各向异性对三分量磁场响应的影响占主导成分;当采集点在x方向距异常体中心小于y方向时,x轴各向异性对三分量响应影响程度大于y轴各向异性,反之亦然。基于本文研究成果,可为各向异性地层条件下瞬变电磁三分量处理解释提供一些有价值的理论借鉴。The conductivity of most formations and fractured water areas is anisotropic,while the anisotropy of formations has great impacts on transient electromagnetic observations,especially on the characteristics of horizontal components.To study the three-component responses of axially anisotropic formations using the transient electromagnetic method,this study introduced a conductivity tensor to construct the governing equation to achieve the three-dimensional three-component forward modeling of the axially anisotropic conductivity using the transient electromagnetic method based on the finite-difference time-domain(FDTD)algorithm.This study verified the accuracy of the three-component forward modeling by comparing the three-dimensional three-component forward modeling results with the one-dimensional analytical results of the isotropic and anisotropic half-space models.Meanwhile,this study established the anisotropic half-space,layered,and water-bearing models and calculated loop-source three-component responses of the transient electromagnetic method.The results are as follows.The horizontal conductivity anisotropy greatly affected the three-component responses.The x-axis anisotropy had greater effects on the B y/t component response than those on B x/t component response,the y-axis anisotropy had greater effects on the B x/t component response than those on the B y/t component response,while the z-axis anisotropy had almost no effect on the three-component responses.Moreover,the three-component responses were primarily affected by conductivity anisotropy of shallow formations.The x-axis anisotropy had greater effects on the three-component responses than the y-axis anisotropy when collection points were closer to an anomaly center in the x-direction than in the y-direction,and vice versa.The results of this study provide some valuable theoretical references for the three-component processing and interpretation of the transient electromagnetic method of anisotropic formations.

关 键 词：轴向 各向异性 瞬变电磁 时域有限差分 三分量 

分 类 号：P631[天文地球—地质矿产勘探]