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首页> 外文期刊>Journal of geophysics and engineering >Attenuation of P-waves due to interlayer fluid flow in hydrate-bearing sediments
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Attenuation of P-waves due to interlayer fluid flow in hydrate-bearing sediments

机译：含水沉积物中层间流体流动引起的P波衰减

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Gas hydrates are currently the focus of intense research covering a broad variety of scientific branches. Numerous field studies, laboratory and numerical experiments have revealed some interesting aspects of sediments containing gas hydrates of which some are still under debate. While there exist several models explaining observed increased seismic velocities, the mechanism of formation of gas hydrates and the reasons for strong attenuation are not fully understood. Two rock physical models are controversially debated: one attributes the occurrence of hydrates to the properties of the rock's matrix, the other relates the presence of hydrates to the properties of the pore fluid. In our approach we assume that an occurrence of hydrates affects both the properties of the fluid and the solid phase of the host sediment. This causes the fluctuations in the elastic properties to become large between the layers of sediments. A poroelastic generalization of the O'Doherty-Anstey theory (ODA-theory) indicates that this would result in increased values for attenuation especially in the seismically relevant lower frequency range. Linking seismic attributes such as velocity and attenuation to statistical properties of material heterogeneities caused by the presence of gas hydrates enables us to numerically evaluate seismic signatures of these heterogeneities and identify parameters responsible for attenuation. To work with realistic models of multilayered, poroelastic media and to account for observed strong fluctuations in hydrate-bearing sedimentary layers we investigate exponentially correlated, randomly layered media. Numerical and analytical results for vertically incident plane P-waves confirm that strong correlated fluctuations in properties of the frame, grain and fluid cause significant and realistic attenuation values (Q_P of 20-30). Results show a significant amount of attenuation taking place in the lower frequency range being caused by interlayer (i.e., mesoscopic) fluid flow. Interlayer flow is promoted by strong heterogeneities in elastic properties between adjacent layers. These heterogeneous layered structures can in a pronounced manner be observed in hydrate-bearing sediments.
机译：天然气水合物目前是广泛研究的重点，涵盖了广泛的科学分支。大量的现场研究，实验室和数值实验已经揭示了含天然气水合物的沉积物的一些有趣方面，其中一些仍在争论中。尽管存在几种解释观测到的地震速度增加的模型，但尚未完全理解天然气水合物的形成机理和强烈衰减的原因。有两种争议的岩石物理模型：一种将水合物的出现归因于岩石基质的性质，另一种将水合物的存在归因于孔隙流体的性质。在我们的方法中，我们假设水合物的出现会影响流体性质和主体沉积物的固相。这导致沉积物各层之间弹性特性的波动变大。 O'Doherty-Anstey理论（ODA理论）的多孔弹性概括表明，这将导致增加的衰减值，特别是在与地震相关的较低频率范围内。将诸如速度和衰减等地震属性与由气体水合物的存在引起的物质异质性的统计特性联系起来，使我们能够从数值上评估这些异质性的地震特征并确定造成衰减的参数。为了与多层多孔弹性介质的现实模型一起工作，并考虑到在含水合物沉积层中观察到的强烈波动，我们研究了指数相关，随机分层的介质。垂直入射平面P波的数值和分析结果证实，框架，颗粒和流体的特性之间强烈的相关波动会导致明显且现实的衰减值（Q_P为20-30）。结果表明，在较低的频率范围内，由于层间（即介观）流体流动而引起大量衰减。相邻层之间弹性特性的强烈异质性促进了层间流动。在含水合物的沉积物中可以明显地观察到这些非均质层状结构。

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