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煤矿老空水是煤矿安全的最大隐患。本文对煤矿老空水的全空间瞬变电磁响应特征进行了数值模拟研究。传统的数值模拟方法不能直接模拟井下全空间瞬变电磁场。我们采用了以多组发射线圈代替传统的单发射回线的方式,使在有限差分法直角网格中加载任意方向发射回线,同时根据全空间特点对磁场的z分量算法进行了改进;根据煤矿实际地质资料建立全空间三维地电模型,采用时域有限差分法模拟了含煤地层中不同位置和不同形态老空水模型的全空间瞬变电磁响应,并分析其视电阻率特征。数值模拟结果表明:煤层与其顶底板电性差异对视电阻率分布产生较大影响,致使视电阻率分布呈以巷道迎头为圆心的近似圆形分布;不同位置和不同形态的老空水模型,其视电阻率等值线低阻异常区与其基本吻合,当老空水位于巷道迎头位置一侧时,由于全空间效应的影响,在另一侧产生一范围相对较小的低阻假异常区,但其等值线数值相对较高。将井下瞬变电磁法应用于实际老空水的探测中,探测资料圈定的老空水位置为后期钻探结果所证实,证明了所提出的方法是合理与有效的。
Old coal mine air safety is the biggest hidden danger. In this paper, the full space transient electromagnetic response characteristics of old empty water in coal mine are numerically simulated. The traditional numerical simulation method can not directly simulate the full space underground transient electromagnetic field. We adopt the method of replacing multiple transmit lanes with traditional single launchers so as to load arbitrary directional launchers in the finite difference method rectangular grid and improve the z component of the magnetic field according to the full space characteristics. Full-space three-dimensional geoelectric model is established based on the actual geologic data of coal mine. The full-space transient electromagnetic response of different locations and different forms of the old water model in coal-bearing strata is modeled by time-domain finite difference method and the apparent resistivity characteristics are analyzed. The numerical simulation results show that the difference of electrical resistivity between coal seam and its top and bottom has a significant impact on the apparent resistivity distribution, resulting in the approximate circular distribution of apparent resistivity in the head center of the tunnel. The low resistivity anomalous zone of apparent resistivity is basically consistent with this. When the old empty water is located on the heading side of the roadway, due to the influence of the full space effect, a relatively low range of low resistivity false anomalous zone is produced on the other side , But its contour is relatively high. The downhole transient electromagnetic method is applied to the detection of actual old empty water, and the location of the old empty water determined by the exploration data is confirmed by the drilling results in the later period, which proves that the proposed method is reasonable and effective.