Analysis of the Velocity Dispersion and Attenuation Behavior of Multi‐Frequency Sonic Logs
Analysis of the Velocity Dispersion and Attenuation Behavior of Multi‐Frequency Sonic Logs
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DOI：
10.4133/1.3614243
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
L. Baron;K. Holliger
中科院分区：
文献类型：
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作者：
L. Baron;K. Holliger
现代小井眼声波测井仪设计用于地面环境和工程应用，允许在覆盖5到10倍频程的带宽上测量多个发射器频率下的P波的相速度和衰减。人们可以探索基于对这种宽带声波测井数据的速度弥散和频率相关衰减的孔隙弹性解释来估计饱和表层冲积层的渗透率的可能性。方法上的考虑表明，对于细粉砂到粗砂范围内的饱和、松散沉积物，以及典型的标称发射器频率范围从1到30 kHz，可观测到的P波速度频散应足够明显，以便根据孔隙弹性地震波传播的理论基础，对底层渗透率结构进行可靠的一阶估计。理论预测还表明，频率依赖的衰减行为应该显示出一个明显的峰值和可检测的变化，为整个范围的松散岩性。关于P波速度频散，结果表明，孔隙弹性的经典框架允许获得一阶估计的渗透性的松散碎屑沉积物的粒度特征之间的细粉砂和粗砂。衰减测量的结果更难以解释，因为推断的衰减值系统地高于理论预测的衰减值，并且它们对频率的依赖形式是可变的，并且仅部分与理论预期一致。渗透率可以说是天然土材料中最重要但最难以捉摸的水力参数，通常只能通过专门的水文实验室和现场实验（例如，Butler，2005）。含水层内渗透率分布的知识是可靠预测流体流动和污染物迁移的关键先决条件。这些信息对于人口密集和/或高度工业化地区日益稀缺和脆弱的地下水资源的有效保护、补救和可持续管理至关重要。一般而言，含水层结构和特别是水力参数分布方面的地球物理制约因素被认为特别有价值。基本方法相对便宜且无创。此外，就空间分辨率和覆盖范围而言，它们有可能弥合传统水文地质方法之间的差距，如岩心分析和示踪剂或抽水试验（例如，Hubbard and Rubin，2005）.虽然标准的传统地球物理技术不能提供任何直接信息的综合介质的渗透性，更专业的方法表现出或多或少的直接敏感性，这一重要参数。沿着核磁共振和光谱激发极化测量，在所谓的孔隙弹性环境中的地震数据的解释可以说代表了达到这一目的的最有希望的途径（例如，Holliger，2008）。地震波在饱和多孔介质中传播的方法论基础一般归功于毕奥（1956 a，1956 b）。瑞士洛桑，洛桑大学地球物理学研究所。
Modern slim-hole sonic-logging tools designed for surficial environmental and engineering applications allow for measurements of the phase velocity and the attenuation of P-waves at multiple emitter frequencies over a bandwidth covering five to 10 octaves. One can explore the possibility of estimating the permeability of saturated surficial alluvial deposits based on the poroelastic interpretation of the velocity dispersion and frequency-dependent attenuation of such broadband sonic-log data. Methodological considerations indicate that for saturated, unconsolidated sediments in the fine silt to coarse sand range and typical nominal emitter frequencies ranging fromapproximately1 to30 kHz, the observable P-wave velocity dispersion should be sufficiently pronounced to allow for reliable first-order estimations of the underlying permeability structure based on the theoretical foundation of poroelastic seismic-wave propagation. Theoretical predictions also suggest that the frequency-dependent attenuation behavior should show a distinct peak and detectable variations for the entire range of unconsolidated lithologies. With regard to the P-wave velocity dispersion, results indicate that the classical framework of poroelasticity allows for obtaining first-order estimates of the permeability of unconsolidated clastic sediments with granulometric characteristics ranging between fine silts and coarse sands. The results of attenuation measurements are more difficult to interpret because the inferred attenuation values are systematically higher than the theoretically predicted ones, and the form of their dependence on frequency is variable and is only partially consistent with theoretical expectations. Introduction Permeability arguably is the most important but most elusive hydraulic parameter in native earthen materials, and it commonly can bemeasured only throughdedicated hydrologic laboratory and field experiments (e.g., Butler, 2005). Knowledge of the permeability distribution within an aquifer is a key prerequisite for reliable predictions of fluid flow and contaminant transport. This information is critical for the effective protection, remediation, and sustainable management of increasingly scarce and fragile groundwater resources in densely populated and/or highly industrialized regions. Geophysical constraints with regard to aquifer structure in general and to the distribution of hydraulic parameters in particular are considered to be especially valuable. The underlying methods are comparatively cheap and noninvasive. In addition, in terms of spatial resolution and coverage, they have the potential to bridge the gap between traditional hydrogeologic methods, such as core analyses and tracer or pumping tests (e.g., Hubbard and Rubin, 2005). Although standard traditional geophysical techniques cannot provide any direct information on the permeability of the integrated medium,more specialized approaches exhibit a more or less direct sensitivity to this important parameter. Along with nuclear magnetic resonance and spectrally induced polarization measurements, the interpretation of seismic data in a so-called poroelastic context arguably represents the most promising avenue to this end (e.g., Holliger, 2008). The methodological foundations of seismic-wave propagation in saturated porous media generally are credited to Biot (1956a, 1956b). The corresponding theoretical Institute of Geophysics, University of Lausanne, Lausanne, Switzerland.