We investigated reflection dispersion characteristics of a poroelastic layer with patchy saturations in seismic low-frequency range. Frequency-dependent attenuation and dispersion of phase velocity were determined with varying fluid saturation, porosity, permeability and heterogeneity size, using analytical solutions of a generalised 1D White’s model proposed here, obtained by incorporating capillary forces into the patchy saturation model. Numerical predictions were employed in combinations with an approximation for the complex and frequency-dependent reflection coefficient from an attenuating thin layer embedded in a dissipative background medium, so as to give a deep insight into the impacts of velocity dispersion and tuning, as well as acoustic impedance contrast, on the seismic low-frequency reflections. Results from this study suggest that wave-induced fluid flow in poroelastic media might account for low-frequency reflection signature anomalies that are associated with fluid saturation in the pore space. We also observed that seismic reflection coefficients of a partially saturated layer can vary strongly versus frequencies, especially in low-frequency range where high attenuation and dispersion can take place due to fluid partial saturation. Analysis of the crossplots of the magnitude for reflection coefficients and dispersion showed that attenuation, dispersion and tuning are more sensitive to gas saturation, porosity, and heterogeneity size. Thus the crossplot provides a useful means for detecting changes in fluid saturation and rock properties.

中文翻译：

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多孔弹性层地震低频反射波频散衰减效应分析

我们研究了地震低频范围内具有不均匀饱和度的多孔弹性层的反射色散特性。相速度的频率相关衰减和色散是根据不同的流体饱和度、孔隙度、渗透率和非均质性大小确定的，使用这里提出的广义一维怀特模型的解析解，通过将毛细管力合并到不规则饱和度模型中获得。数值预测与来自嵌入在耗散背景介质中的衰减薄层的复数和频率相关反射系数的近似值相结合，以便深入了解速度色散和调谐的影响，以及声学阻抗对比，对地震低频反射。这项研究的结果表明，多孔弹性介质中波浪引起的流体流动可能解释了与孔隙空间中的流体饱和度相关的低频反射特征异常。我们还观察到，部分饱和层的地震反射系数随频率变化很大，特别是在低频范围内，由于流体部分饱和会发生高衰减和色散。反射系数和色散幅度的交会图分析表明，衰减、色散和调谐对气体饱和度、孔隙度和非均质性尺寸更敏感。因此，交会图为检测流体饱和度和岩石特性的变化提供了一种有用的手段。