基于粒子群的全空间瞬变电磁二维反演方法研究

Research on two-dimensional inversion method of transient electromagnetic in whole-space based on particle swarm

  • 摘要: 针对煤矿实际采掘情况的复杂性,为了提高探测精度,为钻探提供有效靶点,为矿井水害防治提供可靠的地质资料,研究了基于粒子群的全空间瞬变电磁二维反演方法。通过建立Q型地电模型,开展基于时域有限差分的二维正演模拟,得到不同时刻各网格节点处的磁场强度值;抽取正演模拟得到的磁场强度值与实测资料中的磁场强度值进行最小二乘法反演,采用粒子群算法对电阻率和地层厚度参数进行寻优,使反演结果拟合误差满足精度要求;按测点号依次对最小二乘法反演后的磁场强度值进行全空间瞬变电磁二维反演计算,分析二维反演后得到的瞬变电磁场响应规律和反演精度。实际应用结果表明,基于粒子群的全空间瞬变电磁二维反演方法是可行的,反演结果中的低阻异常体具有成层特性及一定的连通性,更能反映层状地层以砂泥岩为主的岩性结构特征及含水特性,提高了探测精度和分辨率。

     

    Abstract: In order to improve the detection accuracy, provide effective targets for drilling and provide reliable geological information for mine water damage prevention and control, a two-dimensional inversion method of transient electromagnetism in whole-space based on particle swarm is proposed for the complexity of actual mining conditions in coal mines. By establishing a Q-type geoelectric model and carrying out a two-dimensional forward simulation based on finite difference in the time domain, the magnetic field intensity values at each grid node at different times are obtained. The extracted magnetic field intensity values obtained from the forward simulation and the magnetic field intensity values from the measured data are inverted by the least squares method. The particle swarm algorithm is used to optimize the resistivity and formation thickness parameters, so that the fitting error of the inversion results meets the accuracy requirements. According to the measurement point number, the magnetic field intensity values after the least square inversion are calculated by the two-dimensional inversion method of transient electromagnetism in whole-space. Moreover, the transient electromagnetic field response law and inversion accuracy obtained after the two-dimensional inversion are analyzed. The practical application results show that the two-dimensional inversion method of transient electromagnetism in whole-space based on particle swarm is feasible. The low-resistance anomaly in the inversion result has layered characteristics and certain connectivity, which can better reflect the lithological structure characteristics and water-bearing characteristics of the layered formation that dominated by sand and mudstone and improve the detection accuracy and resolution.

     

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