垂直接触带影响下地-井瞬变电磁响应研究  

Research on response of down-hole TEM by vertical sheet

作　　者：徐正玉[1,2] 杨海燕[1,2] 邓居智[2] 汤洪志[3] 张华[2] 谢石文[2] 刘少光[2] 

机构地区：[1]东华理工大学放射性地质与勘探技术国防重点学科实验室,南昌330013 [2]东华理工大学核工程与地球物理学院,南昌330013 [3]东华理工大学勘察设计院,抚州344000

出　　处：《地球物理学进展》2015年第3期1345-1353,共9页Progress in Geophysics

基　　金：江西省教育厅科学技术研究项目资助(GJJ14487);放射性地质与勘探技术国防重点学科实验室开发基金资助项目(RGET1308);国家自然科学基金项目(41004048;41164003;41304097;41264004)资助

摘　　要：地-井瞬变电磁法是利用在地表发射井中接收瞬变场响应来实现勘查矿产资源的一种方法,在钻孔周围一定范围内具有较好的分辨率,能最大限度的发现深部隐藏矿体等优点.因此,被广泛的应用于深部地质结构调查和寻找隐伏矿体中.文中采用时域有限差分法(FDTD),使用大回线源模拟了三维均匀空间中垂直接触带和含有低阻体时垂直接触带响应特征并且深入研究了接触面埋深位置不同和接触面两侧电阻率不同对地-井TEM响应产生的影响.采用非均匀网格剖分技术,在截断边界处使用修正后的廖式吸收边界条件.绘制了磁场对时间导数的等值线图和在井中接收的衰减曲线图.分析表明:受垂直接触带的影响,磁场等值线发生畸变,扩散速度降低衰减变慢,在接触带处形成磁场突变带,响应曲线上呈现为极大值.相比于低阻体,接触面两侧的电阻率比值在数量级上很大时,异常响应的极大值随电阻率比值增大而更加突出,识别界面能力强.总结了地-井TEM响应随接触面埋藏深度增加而减弱,随电阻率增大而呈现先增大后减弱的趋势.本文研究的工作,为今后寻找深部地质结构、判断断层位置以及铀矿成矿环境等地质问题提供了理论依据.Down-hole Transient Electromagnetic Method is a survey method of mineral resource which takes advantage of the transient electromagnetic field transmitted in the surface and measures the transient electromagnetic field responses by receiving coils in the borehole. The advantages of down-hole TEM are that it has better resolution in a certain range around the Bore-hole and it can maximally find the hidden deep ore bodies. Therefore, it was widely used in the investigation of deep geological structures and searching buried ore bodies. In this article, we use the finite-difference time-domain method （FDTD）, a large loop source and non-uniform gird. With regard to boundary condition, we use the correction Liao boundary condition and develop a 3D simulation program, we simulate the responses of vertical sheet and vertical sheet with conductive body. We have studied two factors which influence the down-hole TEM responses, one is the depth of vertical sheet and the other is resistivity of both vertical sheet. Draw the time derivative of the magnetic field contour maps and decay curves of the magnetic field in the borehole. The analyses results indicate that： due to the influence of the vertical sheet, the distortion of contour maps of the magnetic field, the reduction of diffusion rate and decay. However, the magnetic fields appear mutation upon vertical sheet and show max value in decay curves. Compared with the conductive body, when the ratio of resistivity on both sides of the geological body reaches a very high level, the maximum of responses become much more prominent with the increment of resistivity and it has a significant ability of distinguishing interfaces. In conclusion,the responses of down-hole TEM become weaker with the depth of interfaces increasing. With the resistivity increasing, it becomes stronger, and then followed with a .weaker change.This research provides theoretical basis for looking for the deep geological structures and judging the fault location, especially for uranium mineralization

关 键 词：地-井瞬变电磁法 垂直接触带 时域有限差分 数值模拟 特征分析 

分 类 号：P631[天文地球—地质矿产勘探]