1. China Aero Geophysical Survey and Remote Sensing Center for Natural and Resources, Beijing 100083, China 2. Development and Research Center of China Geological Survey, Beijing 100037, China 3. Technical Guidance Center for Mineral Resources of Ministry of Natural Resources, Beijing 100083, China 4. Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
After the induced eddy current in the conductive thin plate is transient, the eddy current distribution has become stable and decays exponentially. In the equivalent mathematical model, it is easier to calculate the late transient electromagnetic response by the equivalent eddy current method. This method can calculate the response of any combination of 1~4 blocks and conductive surrounding rock or cover layer, and has certain applicability. In this paper, the calculation method of late transient electromagnetic equivalent eddy current field induced voltage is deduced. By numerical simulation and typical characteristic analysis of four typical geoelectric models, some results have been obtained: ① When the power-off delay is short, the amplitude of the abnormal response of the conductor is large. When the borehole passes through the center of the abnormal body, the abnormal shape is a single-peak positive abnormal response; with the elapse of time, the electromagnetic response gradually decays. ② When the borehole is located at the boundary of the orebody, the horizontal orebody produces a three-peak symmetrical anomaly, and the anomalous peak value is a negative anomaly; when the inclination is 45°, the anomaly morphology of the orebody exhibits asymmetric positive and negative anomalies, and a negative anomaly appears on the top side of the orebody, with positive anomaly on the underside. ③ Under the same condition, the abnormal amplitude of the simple plate-shaped body is larger than that of the single plate-shaped body, and its abnormal shape conforms to the abnormal response characteristics of the single plate-shaped body. The research results have certain significance for the ground-well transient electromagnetic method to use forward fitting to improve the later interpretation work and to determine the layout parameters of the work area, such as loop size, section length, point distance, and emission current.
I=10 A ; σ均匀大地= 0.01 S/m ; 钻孔偏移距:A孔0 m,B孔80 m,C孔150 m,D孔800 m
Table 1 薄板体瞬变电磁数值模拟参数一览
Fig.2 不同钻孔接收水平单板体模型示意及异常响应曲线
Fig.3 不同钻孔接收倾斜单板体模型示意及异常响应曲线
Fig.4 不同钻孔接收水平多板体纵向组合模型示意及异常曲线
Fig.5 不同钻孔接收倾斜多板体纵向组合模型示意及异常曲线
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