覆盖层下三维板状体地-井瞬变电磁响应

3D inclined conductor behavior of down-hole transient electromagnetic method with overburden layer

地-井瞬变电磁法是地质找矿的有效方法之一,它是利用地表发射、井中接收瞬变场响应来实现查找深部矿产资源的一种方法。在时间域有限差分算法的基础上,以回线源为激发源,采用非均匀网格剖分技术,对均匀半空间和倾斜板状体、含有低阻覆盖层的倾斜板状体模拟。通过对比分析表明:均匀半空间中,响应极大值随观测时间延迟而减小;场源位于接收钻孔正上方时,异常体响应特征明显;当场源位于旁侧位置,需要较长的观测时间获得异常体的响应;低阻覆盖层对异常响应的影响在整个观测时间范围内都存在,减弱了异常体的响应;覆盖层的影响随发射场源与接收钻孔位置距离的增加而减弱。研究工作为定性分析地-井TEM响应特征和资料解释时提供参考。

As one of the effective methods used in search for mineral resources, down-hole transient electromagnetic method （TEM） measures transient electromagnetic field in a drill hole by placing receiving coils in the drill hole. Based on time domain finite difference algorithm, the authors used loop source and non-uniform gird to simulate the response of the uniform medium in half space, inclined conductor, and inclined conductor with overburden. The results indicate that the maximum value of response decreases with delay time in uniform half space. When the source is laid on the receiving drill hole, the abnormal response is reflected apparently. When the source is laid beside the receiving drill hole, abnormal response can be observed with more observation time. The influence of overbur- den exists all over the observation time, which causes the decrease of the abnormal response. It is also weakened with the increasing distance between transmit loop and receiving drill hole. The research provides reference for analysis and interpretation of down-hole TEM abnormal response characteristics.