共查询到20条相似文献,搜索用时 15 毫秒
1.
I. Lerche 《Pure and Applied Geophysics》1985,123(4):503-542
This paper presents the theory which describes how the lateral correlation of vertical displacement is influenced by multiple scattering of seismic waves caused by the presence of fluid-filled fractures, along with an observational methodology to show how to extract fracture-related quantities (e.g. fracture porosity, degree of anisotropy of the fractures, change in orientation of the fractures, density of fluid filling the fractures) from seismic data using the theoretical development as an underpinning framework. A simple physical picture is given of the basic process, as well as some rough order of magnitude estimates to show that the parameters quantifying the size of the multiple scattering fall squarely in the seismic regime.These calculations serve to create a basis to determine, by seismic means ahead of the drill, (1) the degree of fracturing of reservoir rocks (such as the Monterey shale), and (2) the type of fluid filling the fractures. 相似文献
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I. Lerche 《Pure and Applied Geophysics》1987,125(5):717-751
We demonstrate how multiples, generated at the interfaces of plane parallel beds, modify the propagation characteristics of an originally coherent seismic wave. For waves propagating at an angle to the bedding plane we find that theSV andP-waves couple so that neither is a pure mode. TheSH-wave, while modified in its propagation characteristics by multiples, remains a pure mode. The coupling ofSV-multiples into the quasi-P-mode appears weaker than the coupling ofP-wave multiples into the quasi-SV mode; at least this is so for the two simple cases of (a) density fluctuations only and (b) correlatedV
p
andV
s
fluctuations which conserve Poisson's ratio.We also find that the coupling is sensitive to both the angle of propagation and frequency. In addition there is a cut-off angle forP-wave multiples influencing the quasi-SV mode. Propagation angles larger than the cut-off permit theP-multiples to modify the phase of the quasi-SV mode, but not its effective attenuation. No such cut-off effect is found for SV-multiples influencing the quasi-P mode, whose angle-dependent and frequency-dependent phase distortion and effective attenuation are influenced both byP-wave multiples andSV-multiples.In view of the mathematical complexity of the expressions describing the phase, and effective attenuation of modes when allowance is made forP-andS-wave multiples, we strongly advocate numerical coding of the major mathematical formulae. By so doing a systematic study can be undertaken of the frequency and offset dependence of seismic waves as a function of seismic source input and power spectral behavior of the fluctuations in density and elastic constants of beds. It is our opinion that the full mathematical expressions are too involved to permit an analytic, systematic investigation to be given of the phase and attenuation of seismic waves with any degree of sophistication or generality. 相似文献
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本文定义了各向异性黏弹性参数修正因子,并将其引入到黏弹性模型中以体现泥质含量对黏弹性机制的影响,同时将波传播过程中孔隙介质骨架黏弹性力学机制与两种孔隙流体流动力学机制(Biot流动和喷射流动机制)有机地统一起来处理,从而给出了描述含泥质低孔渗孔隙各向异性介质中波传播规律的黏弹性Biot/squirt (BISQ)模型.数值计算结果表明,入射波的方位角、各向异性渗透率以及泥质含量等对含流体复杂孔隙介质中波频散和衰减的影响具有显著的方位各向异性特征,在低频范围内(地震波勘探频率)黏弹性力学机制对波传播能量的衰减起主导作用. 相似文献
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实际地球介质的弹性波衰减,无论是对于地球内部结构反演、含油气储层描述,还是对于地震岩石物理本身的基础研究而言,都十分重要.通过岩石物理实验测量岩石的弹性波衰减是相关研究的基本手段,而谱比法是一种最常用的测量方法.利用谱比法测量的弹性波衰减,简称谱比法衰减,由介质的本征吸收特性和非均质散射特性共同决定.然而,在谱比法理论中,没有将这两种衰减特性的作用区分对待.因此,实验室测量的谱比法衰减中是否含有散射特性,其散射特性是否可以忽略,常不明确.本文基于对岩石物理实验中样品波形特征的基本认识,通过能流理论描述了弹性波的本征吸收和非均质散射过程,以及对应的尾波形成机理.文章还应用能流理论测量岩石的弹性波衰减,即能流法衰减.无论是通过理论推导,还是通过实验验证,谱比法衰减与能流法衰减都显示出良好的一致性.这两种直达波衰减的一致性暗示了谱比法衰减中存在着两种衰减特性.文中还对比分析了谱比法衰减与喷射流本征衰减的实验结果,该结果同样展示了谱比法衰减中可能存在着散射特性.因此,通过能流理论,可以利用样品波形的尾波特征定性判断谱比法衰减中可能存在的散射特性.即异常明显的尾波振幅可能意味着强烈的直达波非均质散射,谱比法衰减中的散射特性因而不可忽略.
相似文献5.
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A. V. Nikolaev 《Pure and Applied Geophysics》1989,131(4):687-702
The processes of seismic wave scattering and dissipation are examined in a medium that, in addition to being inhomogeneous and anelastic, is nonlinear and seismically active (seismic emission). In such a medium, there is a complex interrelation between the effects of nonlinearity, scattering and dissipation. Thus, nonlinear interactions between the various components (primary, scattered and induced) of a developing wavefield cause nonlinear (or wave-on-wave) scattering and, by transferring part of the wave energy to the high-frequency region, contribute to its scattering and dissipation. On the other hand, whereas dissipation opposes the accumulation of nonlinear effects by reducing the wave amplitudes, scattering assists it by increasing the propagation distance (and hence the interaction time).Estimates based on results of field experiments involving vibrators indicate that, as a rule, scattering on inhomogeneities is much stronger than nonlinear scattering, and that nonlinear effects may often dominate dissipative ones.The nonlinearity of the transmitting medium explains observedQ-value anomalies, and its seismic activity explains the existence ofP coda and the temporal changes in codaQ. 相似文献
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In seismic exploration, elastic waves are sent to investigate subsurface geology. However, the transmission and interpretation of the elastic wave propagation is complicated by various factors. One major reason is that the earth can be a very complex medium. Nevertheless, in this paper, we model some terrestrial material as an elastic medium consisting of randomly distributed inclusions with a considerable concentration. The waves incident on such an inhomogeneous medium undergo multiple scattering due to the presence of inclusions. Consequently, the wave energy is redistributed thereby reducing the amplitude of the coherent wave.The coherent or average wave is assumed to be propagating in a homogeneous continuum characterized by a bulk complex wavenumber. This wavenumber depends on the frequency of the probing waves; and on the physical properties and the concentration of discrete scatterers, causing the effective medium to be dispersive. With the help of multiple scattering theory, we are able to analytically predict the attenuation of the transmitted wave intensity as well as the dispersion of the phase velocity. These two sets of data are valuable to the study of the inverse scattering problems in seismology. Some numerical results are presented and also compared, if possible, with experimental measurements. 相似文献
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浙江地区地震波衰减和场地响应研究 总被引:2,自引:2,他引:2
邹振轩 《地震地磁观测与研究》2005,26(6):9-16
根据浙江数字地震台网记录的发生在浙江省及其附近海域的中小地震的波形资料,采用互相衔接的三段几何衰减模型,利用遗传算法联合计算,通过在频率域内的分析,测定和研究了浙江地区剪切波的几何衰减和非弹性衰减以及场地响应的特征。 相似文献
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Wigner-Ville分布及其在地震衰减估计中的应用 总被引:1,自引:1,他引:1
地震信号的衰减一般是在频域内利用信号功率谱的统计性质进行表征。但是,传统的基于傅立叶变换的功率谱估计方法的分辨率较低,使得衰减估计的精度较低。Wigner-Ville分布是一种重要的Cohen类时频分布,它具有一系列的优良性质,如时频边缘分布性质、好的时频聚集性等。这些性质对信号的时频分析具有重要意义。因此,Wigner-Ville分布为地震信号的衰减估计提供了新的手段。本文首先介绍了Wigner-Ville分布以及能够减少或消除交叉项影响的平滑Wigner-Ville分布,然后,提出了一种基于Wigner-Ville分布的衰减估计方法。在这一方法中,利用Wigner-Ville分布得到的瞬时能量谱中高频段的能量下降速率度量衰减。将这一方法应用到塔中地区奥陶系礁滩相碳酸盐岩储层预测,结果表明,基于Wigner-Ville分布的衰减能够有效地检测出礁滩相带和泻湖区域之间衰减特性的差异。 相似文献
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重庆及邻近地区地震烈度衰减关系分析与确定 总被引:6,自引:0,他引:6
根据重庆及邻近地区的地震烈度资料,通过回归分析得到了重庆及邻近地区地震烈度衰减规律。这些研究可供重庆及邻近地区进行地震危险性分析和抗震规划时使用。 相似文献
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A method for the calculation of seismic waves velocities at focal depth is here proposed. A stratified earth model with spherical symmetry and the analytical relationship between the epicentral distance and the travel times of seismic waves are used.This method, applied to the southern Tyrrhenian region and to the Japanese islands, allows to reduce the observed travel times to the focal depth independently of a particular velocity model. 相似文献
13.
Simanchal Padhy 《Physics of the Earth and Planetary Interiors》2005,148(1):1-12
The attenuation characteristics of Indian lithosphere and its comparison with different tectonic settings in the world are determined from the observations of the Q for Lg(QLg)-, and S(QS)-waves in the 1-30 Hz frequency range. The scattering is approximated with a Gaussian distribution of spherical scatterers. To approximate single scattering, we use Dainty's [Geophy. Res. Lett. 8 (11) (1981) 1126] model that attenuation is given by 1/Q(ω) = 1/Qi + g(ω)v/ω, where Qi is intrinsic Q due to anelastic attenuation, v is shear wave velocity, ω is angular frequency, g = ∫n(a)σ da is the total scattering coefficient for S-to-S scattering, n(a) da is the number of scattering spheres of radius a per unit volume, and σ is the scattering cross-section for the sphere. We find that if n(a) is described by a simple two parameter (a0 and c) Gaussian of amplitude c and standard deviation and mean a0, the attenuation data for different regions of the world are well approximated over the frequency band of seismic observations. Our major findings are: (1) the maximum effect of scattering on attenuation occurs at 0.84 Hz or a wavelength of 4.16 km; (2) the values of g are frequency dependent. Values of g are of the order of 10−3 km−1 at 1-30 Hz, varying from 0.0031 to 0.01 and 0.001 to 0.0083 km−1 for tectonically active and stable regions, respectively; (3) regions of active tectonics and seismicity generally have lower Qi values (1000) than that in stable regions (2000); and (4) regions of high Qi value exhibit low intensity of scattering. 相似文献
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简述了改进的最佳匹配地震子波的小波函数构造及参数的物理含义;根据地震波的高、低频分量在黏弹介质中传播时被地层吸收的差异,给出了一种在时-频域定性估计地震波衰减特性的方法;分别以改进的最佳匹配地震子波的小波及Morlet小波作为母小波分析地层吸收特性,并比较了两种小波函数刻画地层吸收特性的能力;测试了这种方法对噪声的敏感程度. 将文中提出的方法用于某油田的一段实测地震资料衰减分析,得到的吸收特性剖面能较好地反映油气的空间展布. 相似文献
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随机弹性介质中地震波散射衰减分析(英文) 总被引:2,自引:0,他引:2
地震波衰减一直是许多学科研究的热点,因为可以反映介质的特性。导致地震波衰减的因素很多,如:传播过程中由于能量扩散导致的几何衰减,固体岩石内部晶粒间相对滑移导致的摩擦衰减,岩石结构不均匀引起的地震波散射衰减。本文主要从统计的观点出发,通过多次数值模拟的方法研究纵波散射在随机弹性介质中所引发的衰减。首先用随机理论建立了二维空间随机弹性介质模型,然后用错格伪谱法的数值方法模拟了波在随机介质中的传播,再通过波场中虚拟检波器的记录,用谱比法估计了弹性波在随机介质中的散射衰减。不同非均匀程度随机弹性介质中的数值结果表明:介质不均匀程度越高,散射衰减越大;在散射体尺寸小于波长的前提下,不同散射体尺寸的计算结果说明:散射体尺寸越大,弹性波衰减越明显。最后提出了一种不均匀孔隙介质中流体流动衰减的方法。通过对随机孔隙介质中地震波的总衰减和散射衰减分别进行了计算,并定量得出了随机孔隙介质中流体流动衰减,结果表明:在实际地震频段下,当介质不均匀尺度101米量级时,散射衰减比流体流动衰减要大,散射衰减是地震波在实际不均匀岩石孔隙介质中衰减的主要原因。 相似文献
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由于介观尺度的孔隙流体流动,弹性波传播过孔隙岩层时在地震频段表现出较强的频散和衰减。Johnson理论给出了在任意孔隙形状的条件下,部分气水饱和孔隙介质的理论相速度和品质因子的解析解。本文在Johnson模型的基础上,通过对Q值曲线的低频和高频近似,推导了Q值曲线的近似公式,以及基于孔隙介质基本地球物理参数和孔隙斑块几何形态参数T和比表面积S/V的最大衰减Qmin近似公式。通过与理论值的对比,对Qmin近似公式存在的线性误差进行改正,进一步提高了精度。复杂的斑块形态对最大衰减Qmin和过渡频率ftr的都产生一定影响,且对ftr影响更大。因为数值模拟直接求解介观尺度的Biot孔隙介质方程需要极大的计算量,我们使用Zener模型建立了等效粘弹模型,有效地模拟了地震频带内的衰减和频散现象。 相似文献
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