Borehole TEM is a configuration in which the transmitter is on the ground and the receiver probe is in borehole. The receiver can be installed near the orebody through the borehole and hence can obtain more reliable information of the orebody. Borehole TEM is effective for conductive mineralization, particularly in areas where the capability of surface EM for defining a target is limited either by large depths or by interfering conductive bodies such as overburden shallow sulfides and peripheral mineralized horizons. Relative to the magnetic source, the detection depth of electric source borehole TEM is deeper and it is more suitable for deep prospecting in the complex terrain area. Through the study of the borehole TEM response characteristics of electrical source of borehole TEM, the authors aim to provide technical support for the application. Three component response characteristics of half space, 1D, 3D model were analyzed through forward modeling, and its validity for different models was proved in this paper. The results show that, due to the superimposition of the background field and anomaly field response upon transient response of total field, the curve shape is complex, and the electrical interfaces are only obviously reflected at the middle and late stage. The shape of the anomalous field curve is relatively simple, and the electrical interface is obvious; the anomaly of the horizontal component is on the whole higher than that of the vertical component. In this paper, by means of numerical simulation analysis, the authors obtained the preliminary understanding of electrical source of downhole TEM three component curve shape and verified the effectiveness of the electrical interface under the condition of the electrical emission sources. The results obtained by the authors can provide a reference for the further research.
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WU Jun-Jie, LI Xiu, ZHI Qing-Quan, DENG Xiao-Hong, ZHANG Jie, WANG Xing-Chun, YANG Yi. A preliminary analysis of anomalous TEM response characteristics in borehole with electric source transmitter. Geophysical and Geochemical Exploration, 2017, 41(1): 129-135.
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