基于异常场的地井瞬变电磁法正演研究

在地 井瞬变电磁正演模拟中,前人均以总场为研究对象,分析响应特征. 此次选择地 井瞬变电磁异常场为研究对象,对单异常体和多异常体以及在"定源异井"和"动源定井"两种观测方式下典型地电模型进行地 井瞬变电磁法三维正演模拟. 首先推导了二次磁场的扩散方程,并用有限差分法进行数值计算. 通过分析以地 井瞬变电磁异常场为研究对象,认为异常场能反映目标体空间几何位置参数. 研究结果表明:在不同钻孔中接收的异常响应随时间推移而衰减减弱,但异常变化特征保持不变;在不同方位布置场源得到的异常响应差异明显,根据其测量结果可判定异常体空间位置信息. 最后总结影响地 井瞬变电磁异常的主要因素有:目标体的埋藏深度、目标体与钻孔之间的耦合关系以及场源的位置关系. 研究结果为相关资料解释提供理论参考.

Research on forward simulation of down-hole TEM based on the abnormal field

In the down-hole TEM forward simulation, previous researchers usually studied total electric field and analyzed response characteristics. In this paper, the authors studied the abnormal field with the down-hole TEM, and simulated the response of single con-duction plate and multiple conduction plates. Meanwhile, the down-hole TEM responses of a three-dimensional conductive plate in a typical half space model were simulated to obtain a"fixed source survey at different drill holes" and"fixed drill hole survey at different source places". First, the authors conducted derivation of difference equation of secondary field and made numerical calculation by u-sing the finite difference method. Comparative studies indicate that during the study of the abnormal field in the down-hole TEM, the abnormal field can reflect the position of anomalous space parameters. The results show that the abnormal response of down-hole TEM becomes weaker with time delay, but the abnormal response characteristics remain unchanged in different drill holes, and the abnormal response difference in different source directions is obvious. The measurement results can be used to judge abnormal body space location information. Finally, the main factors that affect the down-hole TEM abnormal response are the depth of the target body, the coupling relationship between the target body and the drill hole and the source position. The research results provide a theoretical basis for inter-pretation guidelines for related data.