煤层物性参数对瑞雷型槽波频散曲线“交叉”现象的影响

    Influence of Physical Parameters of Coal Seam on “Cross” Phenomenon of Rayleigh In-seam Wave Dispersion Curve

    • 摘要: 瑞雷型地震槽波的相速度和群速度频散曲线,在低频段的基阶和第1高阶模式可能存在“交叉”现象,影响槽波频散曲线的正确拾取。为了研究这种“交叉”现象,设计了典型对称三层岩-煤-岩模型,考虑煤岩介质纵横波速度、密度和煤层厚度等参数的变化,利用广义反射-透射系数算法计算了多组瑞雷型槽波频散曲线,并使用交错网格高阶有限差分数值模拟槽波地震记录,提取频散曲线进行验证。对比分析发现,煤层与围岩横波速度的差异对槽波频散曲线“交叉”现象起着决定性的影响,差异越大,越易产生“交叉”现象;而煤层纵波速度、密度和厚度变化对“交叉”现象影响较小。

       

      Abstract: Dispersion curves of Rayleigh channel waves may have “cross” between the fundamental and first higher order modes either in the phase velocities or in group velocities in the low frequency band. It was observed that such phenomenon can lead to wrong interpretation of dispersion curves. In order to study the cross of dispersion curves, considering the changes of these parameters, such as the velocity and density of the coal seam and country rocks, and the thickness of the coal seam, we present multi-group of dispersion curves of Rayleigh channel waves computed by the generalized reflection-transmission coefficient method, based on a three-layer symmetrical model of rock-coal-rock. What’s more, the staggered-grid higher order finite difference method is used to simulate the channel waves for verification of extracted dispersion curves. Results show that the cross of dispersion curves of the Rayleigh channel waves depend greatly on the S-wave velocity difference between the coal and rocks, more difference, more “cross”, but the influence of thickness, density and P-wave velocity of the coal seam are not significant compared with S-wave velocity.

       

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