煤层工作面槽波三维频散反演成像研究

Research on 3D frequency dispersion inverse imaging of channel wave in coal seam working face

  • 摘要: 目前大多数槽波频散反演煤厚的技术是基于理论频散曲线选择单频进行速度CT层析成像,且反演的工作面煤厚精度不高。为提高煤层工作面煤厚预测精度,计算了多层弹性介质模型的槽波频散曲线,并通过正演模拟验证了三维频散反演方法的有效性。利用广义S变换(Generalized S-Transform,GST)提取实际煤层中Love型槽波频散曲线,通过设置频率范围和步长对工作面进行层析成像,得到不同频率的工作面速度CT成像图。将工作面划分为若干块,根据层析成像结果计算每一块的频散曲线,对每一块频散曲线进行反演,整合反演结果得到整个工作面的速度分布和煤厚分布。频散反演算法选用非线性全局优化算法,如遗传算法、模式搜索算法、粒子群算法和模拟退火算法等,该类算法更容易找到全局最优解从而提高煤厚反演精度。选取某煤矿采煤工作面对槽波三维频散反演技术进行验证,该工作面平均煤厚为3.7 m,采用双巷透射法进行槽波地震勘探,利用广义S变换提取Love槽波每一道频散曲线,在100~250 Hz频段内,每10 Hz提取1次速度,利用层析成像得到16个频率的工作面速度CT成像结果,再根据层析成像结果计算工作面每一块频散曲线,利用遗传算法反演整条频散曲线。结果表明:槽波三维频散反演提高了煤层工作面煤厚预测的精度,对比巷道揭露的煤厚,平均拟合误差仅为0.22 m。因此,槽波三维频散反演成像技术在工作面煤厚预测方面有较高的准确性。

     

    Abstract: At present, most of the techniques for inverting coal thickness through channel wave dispersion are based on the theoretical dispersion curve to select a single frequency for velocity CT tomography imaging, and the accuracy of the inverted coal thickness in the working face is not high. To improve the prediction accuracy of coal thickness in coal seam working faces, the channel wave dispersion curve of the multi-layer elastic medium model is calculated, and the effectiveness of the three-dimensional dispersion inversion method was verified through forward simulation. The dispersion curve of the Love channel wave in the actual coal seam was extracted by using the generalized S-transform. Tomographic imaging of the working face was performed by setting the frequency range and step size, and the velocity CT imaging maps of the working face at different frequencies were obtained. The working face is divided into several sections. The dispersion curves of each section are calculated based on the results of tomographic imaging. The dispersion curves of each section are inverted, and the velocity distribution and coal thickness distribution of the entire working face are obtained by integrating the inversion results. The dispersion inversion algorithm selects nonlinear global optimization algorithms, such as genetic algorithm, pattern search algorithm, particle swarm optimization algorithm and simulated annealing algorithm, etc. This type of algorithm is more likely to find the global optimal solution and thereby improve the accuracy of coal thickness inversion. The three-dimensional dispersion inversion technology of channel waves in the coal mining face of a certain coal mine is selected for verification. The average coal thickness of this working face was 3.7 m. The double-channel transmission method was adopted for channel wave seismic exploration. The generalized S-transform was used to extract each dispersion curve of the Love channel wave, and the velocity was extracted once every 10 Hz within the frequency band of 100−250 Hz. The CT imaging results of the working face velocity at 16 frequencies were obtained by using tomography. Then, each dispersion curve of the working face was calculated based on the tomography results, and the entire dispersion curve was inverted by using the genetic algorithm. The results show that the three-dimensional dispersion inversion of channel waves improves the accuracy of coal thickness prediction in coal seam working faces. Compared with the coal thickness exposed in the roadway, the average fitting error is only 0.22 m. Therefore, the three-dimensional dispersion inversion imaging technology of channel waves has a relatively high accuracy in the prediction of coal thickness in the working face.

     

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