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1.
《应用地球物理》2016,(2)
瑞利波勘探主要是建立在弹性介质分层半空间模型基础上的。当实际地层中包含孔隙介质层时,需要将孔隙介质简化为弹性介质来进行分析和处理。这种简化处理究竟对瑞利波勘探造成怎样的影响是本文所研究的问题。本文基于弹性介质与孔隙介质共同构成的分层半空间模型,首先推导了分层半空间中两种介质处于不同相对位置时的瑞利波频散方程,解决了不同阶数矩阵之间的变量传递问题然后,针对传递矩阵法在求解频散函数时可能出现的溢出问题,给出了一种可以有效提高计算范围的解决方案;同时,提出了一套新的数值算法用于复频散方程的快速求解。数值计算结果表明:当孔隙介质位于半空间表面时对低频瑞利波频散特性的影响最为显著,而在其它情况下对瑞利波频散特性的影响相对较小。 相似文献
2.
波场在含流体的孔隙介质中传播时会产生频散和衰减现象.波场的频散和衰减与孔隙介质的岩石物理属性有关,包括孔隙度、渗透率、流体属性等.现有的三维裂缝/软孔隙网络模型利用椭圆截面纵横比的变化模拟从扁裂缝、软孔隙到硬孔隙的多种情况,而未考虑同时包含孔隙和裂缝的全局性网络空间.为了更好地描述裂缝-孔隙空间,本文提出同时包含裂缝和孔隙的三维裂缝-孔隙网络模型,并给出渗透率的计算方法.通过体积平均法推导了三维裂缝/软孔隙网络模型和三维裂缝-孔隙网络模型的波动方程,利用平面波分析方法得到纵波频散/衰减曲线的表达式,同时应用数值模拟研究了总孔隙度、裂缝孔隙度、裂缝纵横比、裂缝数密度、孔隙流体黏度对纵波衰减和速度频散特征的影响.结果表明,在三维裂缝-孔隙网络模型下,总孔隙度、裂缝参数等对纵波频散衰减特征的影响与三维裂缝/软孔隙网络模型相似.具体表现为:纵波在高频段内出现频散和衰减现象.孔隙度的变化主要影响逆品质因子曲线峰值的大小;裂缝数密度主要控制速度显著变化的范围;裂缝纵横比对纵波速度和特征频率有显著影响. 相似文献
3.
基于单相介质中地震波理论的高频面波法已广泛应用于求取浅地表S波的速度.然而水文地质条件表明,普遍的浅地表地球介质富含孔隙.孔隙中充填的流体会显著地影响面波在浅地表的传播,进而造成频散和衰减的变化.本文研究了地震勘探频段内针对含流体孔隙介质边界条件的面波的传播特性.孔隙流体在自由表面存在完全疏通、完全闭合以及部分疏通的情况.孔隙单一流体饱和时,任何流体边界条件下存在R1模式波,与弹性介质中的Rayleigh波类似,相速度稍小于S波并在地震记录中显示强振幅.由于介质的内在衰减,R1在均匀半空间中也存在频散,相速度和衰减在不同流体边界下存在差异.Biot固流耦合系数(孔隙流体黏滞度与骨架渗透率之比)控制频散的特征频率,高耦合系数会在地震勘探频带内明显消除这种差异.介质的迂曲度等其他物性参数对不同流体边界下的R1波的影响也有不同的敏感度.完全闭合和部分疏通流体边界下存在R2模式波,相速度略低于慢P波.在多数条件下,如慢P波在时频响应中难以观察到.但是在耦合系数较低时会显现,一定条件下甚至会以非物理波形式接收R1波的辐射,显示强振幅.浅表风化层低速带存在,震源激发时的运动会显著影响面波的传播.对于接收点径向运动会造成面波的Doppler频移,横向运动会造成面波的时频畸变.孔隙存在多相流体时,中观尺度下不均匀斑块饱和能很好地解释体波在地震频带内的衰减.快P波受到斑块饱和显著影响,R1波与快P波有更明显关联,与完全饱和模型中不同,也更易于等效模型建立.频散特征频率受孔隙空间不同流体成分比例变化的控制,为面波方法探测浅地表流体分布与迁移提供可能性.通常情况孔隙介质频散特征频率较高,标准线性黏弹性固体可以在相对低频的地震勘探频带内等效表征孔隙介质中R1波的传播特征,特别在时域,可在面波成像反演建模中应用. 相似文献
4.
孔隙介质弹性波传播理论在地球物理勘探、地震工程和岩土动力学等领域有着广泛的应用.而孔隙介质中的弹性波受孔隙度、渗透率、流体黏滞系数等参数的影响,因此研究波场的传播特征将有助于分析和提取这些信息.本文在Biot理论的基础上,针对三维层状孔隙介质模型,利用在合成理论地震图的研究中已经被证实具有稳定、高效且适用范围较广的Luco-Apsel-Chen（LAC）广义反透射方法,给出了弹性波场的一种积分形式的半解析解,可通过数值方法高效、准确地计算层状孔隙介质中的理论波场,所以该积分形式的半解析解可为三维层状孔隙介质波场传播特征的理论数值模拟研究提供一种新的途径和手段. 相似文献
5.
瑞利波具有能量大、信噪比高等特点,可以用来反演介质内部的力学信息,近年来在浅层地球物理勘探、深层地震学研究以及超声波无损检测等多个领域都有较广泛的应用。目前大多数瑞利波的应用中都假设介质是弹性的,然而实际中岩石、土壤和金属等介质都在一定程度上体现出了黏弹性。当介质的黏弹性较强时仍然采用弹性假设研究其中瑞利波的反演将增大误差,因此有必要考虑黏弹性介质中的瑞利波反演,但是目前这方面的研究仍不够深入。本文研究黏弹性介质中瑞利波频散曲线和衰减系数曲线的反演问题,给出其在半空间中联合反演的方法,并对该方法的误差进行分析。 相似文献
6.
地球表层岩石是由不同尺度的岩石骨架、孔隙、以及孔隙中的流体物质相互作用形成的.研究含有孔隙和裂缝的复杂岩石介质中的地震波传播效应一直是石油地球物理勘探领域的热点.因此,许多学者对复杂岩石介质的渗流特征,和地震波的传播与衰减进行了大量的研究.本文在回顾孔隙介质的地震波的传播与衰减理论发展的基础上,首先介绍了孔弹介质的非局部Biot理论,并用它预测负频散现象,然后介绍了实验观测到的波的衰减与岩石物理性质(如孔隙度和渗透率)的关系,最后,给出了对渗流场和地震波的传播与衰减的认识,并对它们之间的相互关系做了一些展望. 相似文献
7.
《应用地球物理》2015,(3)
本文以中观孔隙结构的White模型为基础,构建了部分饱和孔隙介质模型,利用Biot方程的建立思路和Johnson推导的体变模量,推导了部分饱和孔隙介质中的纵波方程,并以平面波为例,求取了方程的衰减系数,分析了地震勘探频带范围内地震波的衰减特性。结果表明:在部分饱和孔隙介质中,地震波在低频段也会发生明显的衰减和频散现象,频率越大,衰减越大;且第二纵波的衰减比第一纵波更为明显;这一结论弥补了Biot理论在描述地震勘探频带范围内波的衰减现象的不足。文中还研究了孔隙度、饱和度和模型内径尺寸对第纵波衰减特性的影响机理,主要表现在在地震勘探频带范围内,波的衰减随孔隙度的增大而增大,随含油气饱和度的增大而减小,当孔隙内径尺寸小于二分之一外径尺寸时,波的衰减随内径尺寸的增大而增大,当内径尺寸大于二分之一外径尺寸时,波的衰减随内径尺寸增大而减小。 相似文献
8.
基于Biot理论,考虑液相的黏弹性变形和固液相接触面上的相对扭转,提出了含黏滞流体VTI孔隙介质模型.从理论上推导出,在该模型中除存在快P波、慢P波、SV波、SH波以外,还将存在两种新横波－慢SV波和慢SH波.数值模拟分析了6种弹性波的相速度、衰减、液固相振幅比随孔隙度、频率的变化规律以及快P波、快SV波的衰减随流体性质、渗透率、入射角的变化规律.结果表明慢SV波和慢SH波主要在液相中传播,高频高孔隙度时,速度较高;大角度入射时,快P波衰减表现出明显的各向异性,而快SV波的衰减则基本不变;储层纵向和横向渗透率存在差异时,快SV波衰减大的方向渗透率高. 相似文献
9.
不同尺度下岩层渗透性与地应力的关系及机理 总被引：3，自引：0，他引：3
无论是地应力场宏观控制区域水文地质条件, 还是微观影响含水介质的渗透特性, 都有其深刻的内在发生机制, 生产实例和实验室试验表明: 在宏观地质大尺度下, 岩层以破碎、位移适应地应力场变化并为地下水的富集及运动提供场所, 地下水则以流动和压力传递来调整含水空间、扩张岩石裂隙实现流固宏观耦合, 尽管地质历史时期构造应力场经历多起叠加改造, 但形成区域主要构造骨架时的地应力场与渗流场具有相当的一致性, 主渗透方向与最大水平主应力方向一致; 在宏观地质中尺度下, 应力变化剧烈区、极低地应力区、应力集中区、剪应力集中区等往往与含水介质的主干裂隙相一致, 地应力均匀变化区则与基质的三重含水介质对应; 在微观地质小尺度下, 岩石空隙为三重孔隙介质, 包括基质孔隙、裂缝孔隙和管道状孔隙, 孔隙度和渗透率是有效应力的函数, 孔隙岩块的孔隙度和渗透率随有效应力的变化关系符合指数型数学模型, 裂缝型岩石宜用幂指数型数学模型描述, 毛细管型岩石则用二次抛物线数学模型描述较为恰当. 裂纹有效压缩系数、闭合压力计算揭示了裂缝性岩芯的渗透率和孔隙度损失较孔隙性岩芯损失大的机理, 裂纹有效压缩系数计算还说明同一介质渗透率变化总是大于孔隙度变化; 厚壁筒理论证实, 实验得出的毛细管型岩石孔隙度和渗透率损失与有效应力的二次抛物线关系正确. 相似文献
10.
横向各向同性介质是地层中普遍存在的一种各向异性介质.本文对径向分层TI孔隙介质包围井孔中激发的斯通利波和弯曲波的传播特性进行了理论计算,发现模式波在低频时更多的是反应原状地层的信息,而随着频率的增加侵入带参数逐渐起控制作用;Biot理论描述的地层衰减比速度更容易受井壁附近地层参数的影响.利用灵敏度曲线定量研究了不同频率下地层各个参数对相速度和衰减系数的贡献大小,主要结果显示模式波的衰减受水平渗透率影响明显,而垂直渗透率的变化对模式波几乎无影响;斯通利波对水平向传播的横波速度比弯曲波的灵敏度高.从单极子和偶极子声源在井孔中激发的全波波形也可发现,声波测井仪器较宽的声源频带和合适的源距设置有利于对不同径向深度上的地层声学参数进行成像. 相似文献
11.
本文通过数值模拟研究了介质黏弹性对瑞雷波传播的影响.模拟采用结合了交错Adams-Bashforth时间积分法、应力镜像法和多轴完美匹配层的标准交错网格高阶有限差分方案.通过模拟结果和理论结果对比,测试了方法的精度,验证了结果的正确性.在均匀半空间模型中,分别从波场快照、波形曲线及频散能量图三个角度,对黏弹性介质瑞雷波衰减和频散特性进行了详细分析.两层速度递增模型被用于进一步分析瑞雷波在黏弹性层状介质中的特性.结果表明：由于介质的黏弹性,瑞雷波振幅发生衰减,高频成分比低频成分衰减更剧烈,衰减程度随偏移距增大而增强;瑞雷波相速度发生频散,且随频率增大而增大,频散能量的分辨率有所降低;黏弹性波动方程中的参考频率,不会影响瑞雷波振幅衰减和相速度频散的程度,但决定了黏弹性和弹性介质瑞雷波相速度相等的频率位置.本研究有助于人们更好地理解地球介质中瑞雷波的行为,并为瑞雷波勘探的应用和研究提供了科学和有价值的参考. 相似文献
12.
An analytical model for describing the propagation and attenuation of Rayleigh waves along the free surface of an elastic porous medium containing two immiscible, viscous, compressible fluids is developed in the present study based on the poroelastic equations formulated by Lo et al. [Lo WC, Sposito G, Majer E. Wave propagation through elastic porous media containing two immiscible fluids. Water Resour Res 2005;41:W02025]. The dispersion equation obtained is complex-valued due to viscous dissipation resulting from the relative motion of the solid to the pore fluids. As an excitation frequency is stipulated, the dispersion equation that is a cubic polynomial is numerically solved to determine the phase speed and attenuation coefficient of Rayleigh waves in Columbia fine sandy loam permeated by an air–water mixture. Our numerical results show that, corresponding to three dilatational waves, there is also the existence of three different modes of Rayleigh wave in an unsaturated porous medium, which are designated as the R1, R2, and R3 waves in descending order of phase speed, respectively. The phase speed of the R1 wave is non-dispersive (frequency-independent) in the frequency range we examined (10 Hz–10 kHz) and decreases as water saturation increases, whose magnitude ranges from 20% to 49% of that of the first dilatational wave with respect to water content. However, it is revealed numerically that the R2 and R3 waves are functions of excitation frequency. Given the same water saturation and excitation frequency, the phase speeds of the R2 and R3 waves are found to be approximately 90% of those of the second and third dilatational waves, respectively. The R1 wave has the lowest attenuation coefficient whereas the R3 wave attenuates highest. 相似文献
13.
Rayleigh面波的频散特性可以用来研究地表浅层结构. 本文使用时域有限差分法来模拟复杂黏弹性介质中的Rayleigh面波,研究了Q值对面波频散特性的影响.文中采用旋转交错网格有限差分,以非分裂卷积形式的完全匹配层为吸收边界,推出了求解二阶位移-应力各向同性黏弹性波动方程的数值方法.为了检验数值解的精度,首先将简单模型的正演结果与解析解对比,验证了方法的正确性;然后模拟了横向缓变层状介质和含有洞穴的介质中的面波,对弹性和黏弹性介质中的面波的频散特性进行对比分析.模拟结果表明浅层Q值对面波的频散特性有显著的影响;强吸收情况下,高阶面波的能量相对低阶面波能量显著增强. 相似文献
14.
Rayleigh wave exploration is based on an elastic layered half-space model. If practical formations contain porous layers, these layers need to be simplified as an elastic medium. We studied the effects of this simplification on the results of Rayleigh wave exploration. Using a half-space model with coexisting porous and elastic layers, we derived the dispersion functions of Rayleigh waves in a porous layered half-space system with porous layers at different depths, and the problem of transferring variables to matrices of different orders is solved. To solve the significant digit overflow in the multiplication of transfer matrices, we propose a simple, effective method. Results suggest that dispersion curves differ in a lowfrequency region when a porous layer is at the surface; otherwise, the difference is small. 相似文献
15.
Louis Martel 《Pure and Applied Geophysics》1976,114(5):811-820
A numerical method is developed which can be used to determine the characteristics of Rayleigh wave propagation in a homogeneous medium where, at each surface point, the radius of curvature is large compared to the wavelength of Rayleigh waves. This method is deduced from experimental results on seismic modeling of some simple cases.In the general case we compute two effects of surface topography on the Rayleigh waves: a dispersion and attenuation of the waves due to the whole path and a local modulation of the displacement components depending on the local curvature. Therefore, both effects are not to be neglected in the case of precise measurement of the velocities and of the amplitudes from which the attenuation factor is carried out. 相似文献
16.
Jianghai Xia Yixian Xu Chao Chen Ronald D. Kaufmann Yinhe Luo 《Soil Dynamics and Earthquake Engineering》2006,26(5):395-403
We discuss five useful equations related to high-frequency surface-wave techniques and their implications in practice. These equations are theoretical results from published literature regarding source selection, data-acquisition parameters, resolution of a dispersion curve image in the frequency–velocity domain, and the cut-off frequency of high modes. The first equation suggests Rayleigh waves appear in the shortest offset when a source is located on the ground surface, which supports our observations that surface impact sources are the best source for surface-wave techniques. The second and third equations, based on the layered earth model, reveal a relationship between the optimal nearest offset in Rayleigh-wave data acquisition and seismic setting—the observed maximum and minimum phase velocities, and the maximum wavelength. Comparison among data acquired with different offsets at one test site confirms the better data were acquired with the suggested optimal nearest offset. The fourth equation illustrates that resolution of a dispersion curve image at a given frequency is directly proportional to the product of a length of a geophone array and the frequency. We used real-world data to verify the fourth equation. The last equation shows that the cut-off frequency of high modes of Love waves for a two-layer model is determined by shear-wave velocities and the thickness of the top layer. We applied this equation to Rayleigh waves and multi-layer models with the average velocity and obtained encouraging results. This equation not only endows with a criterion to distinguish high modes from numerical artifacts but also provides a straightforward means to resolve the depth to the half space of a layered earth model. 相似文献
17.
Joint inversion of Rayleigh‐wave dispersion data and vertical electric sounding data: synthetic tests on characteristic sub‐surface models 
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下载免费PDF全文 In the traditional inversion of the Rayleigh dispersion curve, layer thickness, which is the second most sensitive parameter of modelling the Rayleigh dispersion curve, is usually assumed as correct and is used as fixed a priori information. Because the knowledge of the layer thickness is typically not precise, the use of such a priori information may result in the traditional Rayleigh dispersion curve inversions getting trapped in some local minima and may show results that are far from the real solution. In this study, we try to avoid this issue by using a joint inversion of the Rayleigh dispersion curve data with vertical electric sounding data, where we use the common‐layer thickness to couple the two methods. The key idea of the proposed joint inversion scheme is to combine methods in one joint Jacobian matrix and to invert for layer S‐wave velocity, resistivity, and layer thickness as an additional parameter, in contrast with a traditional Rayleigh dispersion curve inversion. The proposed joint inversion approach is tested with noise‐free and Gaussian noise data on six characteristic, synthetic sub‐surface models: a model with a typical dispersion; a low‐velocity, half‐space model; a model with particularly stiff and soft layers, respectively; and a model reproduced from the stiff and soft layers for different layer‐resistivity propagation. In the joint inversion process, the non‐linear damped least squares method is used together with the singular value decomposition approach to find a proper damping value for each iteration. The proposed joint inversion scheme tests many damping values, and it chooses the one that best approximates the observed data in the current iteration. The quality of the joint inversion is checked with the relative distance measure. In addition, a sensitivity analysis is performed for the typical dispersive sub‐surface model to illustrate the benefits of the proposed joint scheme. The results of synthetic models revealed that the combination of the Rayleigh dispersion curve and vertical electric sounding methods in a joint scheme allows to provide reliable sub‐surface models even in complex and challenging situations and without using any a priori information. 相似文献
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The three-dimensional thin layer element method is formulated for the dynamic response analysis of an axi-symmetric structure in submerged soil. Biot's wave equation for fluid-filled porous medium is used in the formulation. The three-dimensional thin layer element method computes the wave numbers and their associated mode shapes, for both Rayleigh waves and Love waves in submerged soil, which define the characteristics of the waves. The submerged condition affects the characteristics of the Rayleigh waves in soil. As a result, it alters substantially the soil-structure interaction stresses if the permeability of the soil is relatively large and, to less extent, the response of the structure. The thin layer element method is far more efficient than the finite element method for analyzing the fluid-filled porous medium, yet capable of taking into account a multi-layered inhomogeneous soil. 相似文献
19.
Dispersion of Rayleigh type surface wave propagation has been discussed in four-layered oceanic crust. It includes a sandy layer over a crystalline elastic half-space and over it there are two more layers—on the top inhomogeneous liquid layer and under it a liquid-saturated porous layer. Frequency equation is obtained in the form of determinant. The effects of the width of different layers as well as the inhomogeneity of liquid layer, sandiness of sandy layer on surface waves are depicted and shown graphically by considering all possible case of the particular model. Some special cases have been deduced, few special cases give the dispersion equation of Scholte wave and Stoneley wave, some of which have already been discussed elsewhere. 相似文献