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1.
横向各向同性介质是地球内部广泛分布的一种各向异性介质.针对这种介质，我们对各向同性介质的最小走时树走时模拟方法进行了推广，推广后的方法可适用于非均匀、对称轴任意倾斜的横向各向同性介质模型.为保证计算效率，最小走时树的构建采用了一种子波传播区域随地震波传播动态变化的改进算法.对于弱各向异性介质，我们使用了一种新的地震波群速度近似表示方法，该方法基于用射线角近似表示相角的思想，对3种地震波（qP, qSV和qSH）均有较好的精度.应用本文地震波走时模拟方法对均匀介质、横向非均匀介质模型进行了计算，并将后者结果与弹性波方程有限元方法的模拟结果进行了对比，结果表明两者符合得很好.本文方法可用于横向各向同性介质的深度偏移及地震层析成像的深入研究. 相似文献
2.
由所建立的三维qP波相速度表示式出发，导出并解析求解各向异性介质中的频散方程，得到三维各向异性介质中的相移算子，进而将以相移算子为基础的对称非平稳相移方法推广到各向异性介质，发展了一个三维各向异性介质的深度偏移方法. 文中使用的各向异性介质的速度模型与现行的各向异性构造的速度估计方法一致，将各向同性、弱各向异性及强各向异性统一在一个模型中. 所建立的各向异性介质对称非平稳相移波场延拓算子可以同时适应速度及各向异性参数横向变化；文中给出的算例虽然是针对二维VTI介质的，但所提出的算法同样适用于三维TI介质. 相似文献
3.
利用交错网格有限差分和旋转交错网格有限差分进行各向异性介质弹性波场数值模拟时, 质点振动速度分量与应力张量的网格节点定义方式均不相同, 从而对各向异性波场分离效果产生不同的影响. 针对这一问题, 本文以具有垂直对称轴的横向各向同性(VTI)介质的波场分离为例, 首先分析了两种网格的参数定义方式以及VTI介质波场的分离过程; 其次, 详细研究和分析了这两种网格的参数定义方式对各向异性介质波场分离的影响, 并依据波前面连续性以及波场分离效果等方面, 通过数值模拟实验对该影响进行分析验证. 结果表明, 旋转交错网格的参数定义方式更有利于进行各向异性介质波场数值模拟和波场分离. 相似文献
4.
正交各向异性介质P波走时分析及Thomsen参数反演 总被引：10，自引：3，他引：10
对于包含有垂向裂缝的横向各向同性地层或含有多组正交裂缝的各向同性地层，正交各向异性介质模型是最简单的与实际地层相符的方位各向异性模型.本文对单层水平反射界面正交各向异性模型采用射线追踪法计算了全方位角变化的P波走时，时距曲线表现出强方位各向异性.采用小生境遗传算法，对三条成一定角度的测线的走时信息进行速度和各向异性参数反演.模型算例表明，此方法可以得到高精度的裂缝方位角、P波垂直速度和较高精度的Thomsen各向异性参数. 相似文献
5.
地球介质相对于地震波波长尺度的定向非均匀性会导致波速的各向异性,进而影响地震波场的运动学与动力学特征．各向异性弹性波动方程是描述该类介质波场传播的基本工具,在正演模拟、偏移成像与参数反演中起着关键作用．为了面向实际应用构建灵活、简便的各向异性波场传播算子,人们一直在寻求简化的各向异性波动方程．本文借鉴各向异性弹性波波型分离思想,通过对平面波形式的弹性波方程(即Christoffel方程)实施一种代表向波矢量方向投影的相似变换,推导出了一种适应任意各向异性介质、运动学上与原始弹性波方程完全等价,在动力学上突出qP波的新方程,即qP波伪纯模式波动方程．文中以横向各向同性(TI)介质为例,给出了相应的qP波伪纯模式波动方程及其声学与各向同性近似,并在此基础上开展了正演模拟和逆时偏移试验,展示了这种描述各向异性波场传播的新方程的特点与优势． 相似文献
6.
裂缝介质横波分裂时差影响因素定量研究 总被引：1，自引：0，他引：1
裂缝介质数值模拟是研究裂缝型油藏各向异性及裂缝检测的关键.横波分裂现象是波在各向异性介质中传播的一个显著特征,横波分裂时差能够反映地下裂隙密度和介质物性等信息.本文给出二维均匀TTI介质在不同极化角度下的横波群速度公式,进而得到偏移距表征的横波分裂时差表达式;同时采用二维三分量交错网格高阶有限差分方法模拟不同极化角度下的三分量炮记录,与理论值对比分析,定量研究分裂时差与极化角、偏移距、各向异性参数的关系,得到如下主要结论:1)在不同各向异性强度下,横波分裂时差与极化角呈现不同的变化规律,而快慢横波振幅比与极化角的关系不受各向异性强度的影响;2)从能量角度,在45°～55°极化角内,横波传播的能量对比最强,是观测横波分裂的最佳角度范围;3)表征各向异性强度的三个参数中γ对横波分裂时差的影响最大,其从0变化到0.3,分裂时差增幅达432.4%. 相似文献
7.
转换波偏移可以利用纵横波波场信息,得到高分辨率的成像结果,从而为油藏描述提供高质量的地震资料.目前的研究主要是利用纵波波场信息进行偏移成像,然而,传统的纵波方法在复杂探区成像时具有一定的局限性.为此,本文在各向异性介质声波射线追踪算法的基础上,推导出各向异性介质转换波射线追踪方程,发展了一种转换波射线追踪算法;并将研究的追踪算法应用到偏移成像中,提出了一种各向异性VTI介质角度域转换波高斯束偏移成像方法.通过各向异性VTI介质断块模型和复杂构造模型试算,说明了本文方法的正确性和有效性.模型试算的结果表明,在考虑地下各向异性时,本文研究的方法具有更好的成像效果,提取的角道集结果可以为偏移速度分析提供依据. 相似文献
8.
平面波分解法是研究地震波场简捷有效的方法,各种复杂的波场可用平面波合成的方法得到．文中采用平面波方法研究非均匀各向异性介质中的弹性波．对时空域非均匀各向异性介质波动方程,运用f-k变换,可得到频率空间域波动方程(Christoffel方程)．利用非均匀各向异性介质中,弹性参数及其空间变化率与Christoffel矩阵元素关系,提出非均匀各向异性介质Christoffel矩阵方程的求解方法,并运用于非均匀TIV介质和非均匀EDA介质．在连续介质条件下,当波沿速度增加方向传播时,振幅的方向导数小于零,即振幅衰减;当波沿速度减小方向传播时,振幅的方向导数大于零,即振幅增强．波的振幅强度是传播方向的函数(各向同性条件下也是如此),但并不总是衰减．若只研究波沿速度增加方向传播的情况即得出波在连续介质中传播振幅衰减的结论是不全面的． 相似文献
9.
随着多分量采集技术的发展,弹性波逆时偏移技术在三维各向异性介质复杂地质构造成像中得到了广泛的应用.然而耦合的P波场和S波场,会在传播过程中产生串扰噪声,降低弹性波逆时偏移的成像精度.为了解决这一问题,本研究针对具有倾斜各向异性对称轴的三维横向各向同性(Transverse Isotropy, TI)介质,提出了一种矢量弹性波场快速解耦方法,可以有效提高偏移剖面的成像质量.该方法首先通过坐标转换,将观测系统坐标系的垂直轴旋转到TI介质的对称轴方向,在新坐标系下,根据具有垂直对称轴的三维横向各向同性(Vertical Transverse Isotropy, VTI)介质中的分解算子,推导出三维TI介质解耦算子表达式.接着引入一种在空间域快速计算分解波场的方法,来实现空间域矢量P波场和S波场分离,极大地提高了计算效率.最后,通过点积成像条件,将提出的P/S波分解方法引入到三维TI介质弹性波逆时偏移中,得到高精度的PP和PS成像.与以往的波场分解方法相比,本文方法具有数值稳定和计算效率高的特点.数值算例表明,应用上述三维TI分解算子得到的偏移剖面有效压制了噪声,提高了成像质量. 相似文献
10.
二维横各向同性弹性随机介质中的波场特征 总被引：9，自引：4，他引：5
本文通过交错网格有限差分正演．模拟了平面地震波在二维横各向同性弹性随机介质模型中的传播及其自激自收时间记录．为研究横各向同性弹性随机介质模型中的波场特征,我们在五个不同的时间区段上,分别计算剖面的三个统计特征(横向中心频率、纵向中心频率、波场能量相对值)．这样,对应每一个横各向同性弹性随机介质模型．均可计算得到15个不同的波场特征量．我们通过在二维横各向同性弹性随机介质中的正演模拟．研究当自相关长度以及介质的各向异性系数变化时,对应的上述波场特征量的变化特点．证实了在随机介质模型中．各向异性系数的变化会引起波场记录上的某些统计特征的变化,归纳得出了若干结论． 相似文献
11.
Yongming Lu Qiancheng Liu Jianfeng Zhang Kai Yang Hui Sun 《Geophysical Prospecting》2019,67(5):1296-1311
With the progress in computational power and seismic acquisition, elastic reverse time migration is becoming increasingly feasible and helpful in characterizing the physical properties of subsurface structures. To achieve high-resolution seismic imaging using elastic reverse time migration, it is necessary to separate the compressional (P-wave) and shear (S-wave) waves for both isotropic and anisotropic media. In elastic isotropic media, the conventional method for wave-mode separation is to use the divergence and curl operators. However, in anisotropic media, the polarization direction of P waves is not exactly parallel to the direction of wave propagation. Also, the polarization direction of S-waves is not totally perpendicular to the direction of wave propagation. For this reason, the conventional divergence and curl operators show poor performance in anisotropic media. Moreover, conventional methods only perform well in the space domain of regular grids, and they are not suitable for elastic numerical simulation algorithms based on non-regular grids. Besides, these methods distort the original wavefield by taking spatial derivatives. In this case, a new anisotropic wave-mode separation scheme is developed using Poynting vectors. This scheme can be performed in the angle domain by constructing the relationship between group and polarization angles of different wave modes. Also, it is performed pointwise, independent of adjacent space points, suitable for parallel computing. Moreover, there is no need to correct the changes in phase and amplitude caused by the derivative operators. By using this scheme, the anisotropic elastic reverse time migration is more efficiently performed on the unstructured mesh. The effectiveness of our scheme is verified by several numerical examples. 相似文献
12.
The phase and group velocity surfaces are essential for wave propagation in anisotropic media. These surfaces have certain features that, especially, for shear waves result in complications for modelling and inversion of recorded wavefields. To analyse wave propagation in an anisotropic model, it is important to identify these features in both the phase and group domains. We propose few characteristics for this analysis: the energy flux angle, decomposed in the polar and azimuth angle correction angles and enhancement factor, which is able to characterize both singularity points and triplication zones. The very simple equation that controls the triplications is derived in the phase domain. The proposed characteristics are illustrated for elastic and acoustic anisotropic models of different symmetry classes. 相似文献
13.
Paul Sava 《Geophysical Prospecting》2012,60(1):29-48
Seismic waves propagate through the earth as a superposition of different wave modes. Seismic imaging in areas characterized by complex geology requires techniques based on accurate reconstruction of the seismic wavefields. A crucial component of the methods in this category, collectively known as wave‐equation migration, is the imaging condition that extracts information about the discontinuities of physical properties from the reconstructed wavefields at every location in space. Conventional acoustic migration techniques image a scalar wavefield representing the P‐wave mode, in contrast to elastic migration techniques, which image a vector wavefield representing both the P‐ and S‐waves. For elastic imaging, it is desirable that the reconstructed vector fields are decomposed into pure wave modes, such that the imaging condition produces interpretable images, characterizing, for example, PP or PS reflectivity. In anisotropic media, wave mode separation can be achieved by projection of the reconstructed vector fields on the polarization vectors characterizing various wave modes. For heterogeneous media, because polarization directions change with position, wave mode separation needs to be implemented using space‐domain filters. For transversely isotropic media with a tilted symmetry axis, the polarization vectors depend on the elastic material parameters, including the tilt angles. Using these parameters, we separate the wave modes by constructing nine filters corresponding to the nine Cartesian components of the three polarization directions at every grid point. Since the S polarization vectors in transverse isotropic media are not defined in the singular directions, e.g., along the symmetry axes, we construct these vectors by exploiting the orthogonality between the SV and SH polarization vectors, as well as their orthogonality with the P polarization vector. This procedure allows one to separate all three modes, with better preserved P‐wave amplitudes than S‐wave amplitudes. Realistic synthetic examples show that this wave mode separation is effective for both 2D and 3D models with strong heterogeneity and anisotropy. 相似文献
14.
在各向异性地震波场中,qP波与qS波常常是耦合在一起的.多分量地震数据处理中一个关键环节就是波型分离(即模式解耦),以纵波成分为主的常规单分量地震数据的成像则需要合理描述标量qP波的传播算子.本文作者曾构建了在运动学上同弹性波动方程等价,动力学上突出标量qP波的伪纯模式波动方程.为了彻底消除qS波残余,本文根据波矢量与qP波偏振矢量之间的偏差,提出从伪纯模式波场提取纯模式标量qP波的方法.数值分析展示了投影偏差算子在波数域和空间域的特征.基于不同复杂程度理论模型的试验结果表明,联合"伪纯模式传播算子"与"投影偏差校正"可为各向异性介质分离模式波场传播过程提供一种简便的描述工具. 相似文献
15.
Yanadet Sripanich Sergey Fomel Junzhe Sun Jiubing Cheng 《Geophysical Prospecting》2017,65(5):1231-1245
The goal of wave‐mode separation and wave‐vector decomposition is to separate a full elastic wavefield into three wavefields with each corresponding to a different wave mode. This allows elastic reverse‐time migration to handle each wave mode independently. Several of the previously proposed methods to accomplish this task require the knowledge of the polarisation vectors of all three wave modes in a given anisotropic medium. We propose a wave‐vector decomposition method where the wavefield is decomposed in the wavenumber domain via the analytical decomposition operator with improved computational efficiency using low‐rank approximations. The method is applicable for general heterogeneous anisotropic media. To apply the proposed method in low‐symmetry anisotropic media such as orthorhombic, monoclinic, and triclinic, we define the two S modes by sorting them based on their phase velocities (S1 and S2), which are defined everywhere except at the singularities. The singularities can be located using an analytical condition derived from the exact phase‐velocity expressions for S waves. This condition defines a weight function, which can be applied to attenuate the planar artefacts caused by the local discontinuity of polarisation vectors at the singularities. The amplitude information lost because of weighting can be recovered using the technique of local signal–noise orthogonalisation. Numerical examples show that the proposed approach provides an effective decomposition method for all wave modes in heterogeneous, strongly anisotropic media. 相似文献
16.
本文将DRP/opt MacCormack有限差分格式用于模拟二维各向异性介质中的地震波传播.DRP/opt MacCormack是一种同位网格下的差分格式,避免了传统的交错网格在计算各向异性问题时由于变量插值而导致的误差.而且相对于低阶同位网格差分格式,它具有低色散、低耗散的优点.此格式将中心差分算子分成前向和后向两个空间单边差分,然后在4-6步Runge-Kutta时间积分中使用单边差分组合.在具有垂直对称轴的横向各向同性（VTI）模型下,通过对比DRP/opt MacCormack有限差分和谱元方法的模拟结果,验证了前者具有很高的精度和稳定性.由于实际地质条件下TI介质的对称轴通常是倾斜的(TTI),本文在二维三分量框架下模拟TTI介质中的地震波场.结果显示横波分裂和切平面/反平面运动耦合的特征.数值实验表明DRP/opt MacCormack是一种有效的研究各向异性介质中地震波传播规律的差分格式. 相似文献
17.
由于构造运动等作用,TI介质对称轴往往沿空间任意方向分布,具有任意空间取向对称轴的TI（ATI）介质更符合实际地质情况.VTI介质与ATI介质的相速度在形式上具有一致性,VTI介质中地震波的相角对应ATI介质对称轴与地震波传播方向的夹角.本文基于Tsvankin的VTI介质精确相速度公式,利用TI介质对称轴和地震波传播方向上单位向量的数量积和向量积来计算ATI介质的精确相速度.根据弱各向异性假设,导出qP波和qSV波的近似相速度,分析了近似公式的误差,讨论总结了ATI介质qP波和qSV波的相速度特征.本文中的单位向量采用观测坐标系表示,通过相角关系,可以较为方便地由ATI介质近似相速度导出频散关系,然后借助傅里叶逆变换推导出时间-波数域qP波和qSV波解耦的波动方程.数值算例表明本文的波动方程是qP波和qSV波解耦的,波场计算结果稳定,未出现明显的数值频散,验证了本文方法的有效性. 相似文献
18.
Characterizing the expressions of seismic waves in elastic anisotropic media depends on multiparameters. To reduce the complexity, decomposing the P-mode wave from elastic seismic data is an effective way to describe the considerably accurate kinematics with fewer parameters. The acoustic approximation for transversely isotropic media is widely used to obtain P-mode wave by setting the axial S-wave phase velocity to zero. However, the separated pure P-wave of this approach is coupled with undesired S-wave in anisotropic media called S-wave artefacts. To eliminate the S-wave artefacts in acoustic waves for anisotropic media, we set the vertical S-wave phase velocity as a function related to propagation directions. Then, we derive a pure P-wave equation in transversely isotropic media with a horizontal symmetry axis by introducing the expression of vertical S-wave phase velocity. The differential form of new expression for pure P-wave is reduced to second-order by inserting the expression of S-wave phase velocity as an auxiliary operator. The results of numerical simulation examples by finite difference illustrate the stability and accuracy of the derived pure P-wave equation. 相似文献
19.
Munirdin Tohti Yibo Wang Evert Slob Yikang Zheng Xu Chang Yi Yao 《Geophysical Prospecting》2020,68(6):1927-1943
Seismoelectric coupling in an electric isotropic and elastic anisotropic medium is developed using a primary–secondary formulation. The anisotropy is of vertical transverse isotropic type and concerns only the poroelastic parameters. Based on our finite difference time domain algorithm, we solve the seismoelectric response to an explosive source. The seismic wavefields are computed as the primary field. The electric field is then obtained as a secondary field by solving the Poisson equation for the electric potential. To test our numerical algorithm, we compared our seismoelectric numerical results with analytical results obtained from Pride's equation. The comparison shows that the numerical solution gives a good approximation to the analytical solution. We then simulate the seismoelectric wavefields in different models. Simulated results show that four types of seismic waves are generated in anisotropic poroelastic medium. These are the fast and slow longitudinal waves and two separable transverse waves. All of these seismic waves generate coseismic electric fields in a homogenous anisotropic poroelastic medium. The tortuosity has an effect on the propagation of the slow longitudinal wave. The snapshot of the slow longitudinal wave has an oval shape when the tortuosity is anisotropic, whereas it has a circular shape when the tortuosity is isotropic. In terms of the Thomsen parameters, the radiation anisotropy of the fast longitudinal wave is more sensitive to the value of ε, while the radiation anisotropy of the transverse wave is more sensitive to the value of δ. 相似文献
20.
黏弹各向异性介质中传播不均匀波，其反射、透射模式不仅与介质分界面两侧速度对比有关，还与品质因子Q的对比有关. 用伪谱技术模拟黏弹各向异性介质分界面上波的反射、透射，并与弹性各向异性介质、黏弹各向同性介质和弹性各向同性介质的模拟结果做比较. 计算平面波的反射、透射系数，分析介质的黏弹性和各向异性对反射、透射系数的影响. 数值模拟了一个三层介质模型中的波场，分析两个分界面上产生的反射波的特征. 黏弹各向异性介质中，qS波比qP波衰减程度大. 相似文献