Whole-space transient electromagnetic detection of water-bearing goaf
CHEN Jian-Qiang1,2,3(), LI Yan-Chuan3, TIAN Hao3, LI Han-Chao3
1. Mine Safety Technology Research Branch of China Coal Research Institute, Beijing 100013, China 2. State Key Laboratory of Coal Mining and Clean Utilization, China Coal Research Institute, Beijing 100013, China 3. Jincheng Anthracite Mining Group Technology Research Co., Ltd., Jincheng 048006, China
Aiming at tackling the problem of whole-space transient electromagnetic response signal identification in water-bearing goaf and based on induced electromotive force (EMF)-apparent resistivity and time-depth conversion relationship, the authors obtained the spatial distribution law of apparent resistivity with depth variation of the whole sector by using the finite element numerical simulation and field measurement method, extracted the EMF attenuation curve of the measuring point in the low resistance abnormal area, and calculated the voltage rise amplitude of the measuring point varying with the detection angle. Based on the above research, the authors carried out the drilling verification and borehole peeping, and analyzed the content of the drilling water samples. The results show that the transverse angle consistency of transient electromagnetic response of water-bearing goaf is higher than that of vertical depth, and the rising amplitude of EMF in the abnormal region of low resistance is opposite to the difference of induced voltage, which shows a sharp increase in the initial stage of secondary field observation followed by slowing down, reaching more than 10 times on the whole. Drilling engineering and geochemical exploration analysis further verify the geophysical exploration results.
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