共查询到20条相似文献，搜索用时 271 毫秒
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Sylvain Nguyen † Reda Baina Mathias Alerini ‡ Gilles Lambaré Vincent Devaux Mark Noble 《Geophysical Prospecting》2008,56(5):613-625
Depth velocity model building remains a difficult step within the seismic depth imaging sequence. Stereotomography provides an efficient solution to this problem but was limited until now to a picking of seismic data in the prestack time un-migrated domain. We propose here a method for stereotomographic data picking in the depth migrated domain. Picking in the depth migrated domain exhibits the advantage of a better signal-to-noise ratio and of a more regular distribution of picked events in the model, leading to a better constrained tomographic inverse problem. Moreover, any improvement on the velocity model will improve the migrated results, again leading to improved picking. Our strategy for obtaining a stereotomographic dataset from a prestack depth migration is based on migration of attributes (and not on a kinematic demigration approach!). For any locally coherent event in the migrated image, migration of attributes allows one to compute ray parameter attributes corresponding to the specular reflection angle and dip. For application to stereotomography, the necessary attributes are the source/receiver locations, the traveltime and the data slopes. For the data slope, when the migration velocity model is erroneous, some additional corrections have to be applied to the result of migration of the attributes. Applying these corrections, our picking method is theoretically valid whatever the quality of the migration velocity model. We first present the theoretical aspects of the method and then validate it on 2D synthetic and real seismic reflection data sets. 相似文献
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Wave-equation migration velocity analysis. I. Theory 总被引：2，自引：0，他引：2
We present a migration velocity analysis (MVA) method based on wavefield extrapolation. Similarly to conventional MVA, our method aims at iteratively improving the quality of the migrated image, as measured by the flatness of angle‐domain common‐image gathers (ADCIGs) over the aperture‐angle axis. However, instead of inverting the depth errors measured in ADCIGs using ray‐based tomography, we invert ‘image perturbations’ using a linearized wave‐equation operator. This operator relates perturbations of the migrated image to perturbations of the migration velocity. We use prestack Stolt residual migration to define the image perturbations that maximize the focusing and flatness of ADCIGs. Our linearized operator relates slowness perturbations to image perturbations, based on a truncation of the Born scattering series to the first‐order term. To avoid divergence of the inversion procedure when the velocity perturbations are too large for Born linearization of the wave equation, we do not invert directly the image perturbations obtained by residual migration, but a linearized version of the image perturbations. The linearized image perturbations are computed by a linearized prestack residual migration operator applied to the background image. We use numerical examples to illustrate how the backprojection of the linearized image perturbations, i.e. the gradient of our objective function, is well behaved, even in cases when backprojection of the original image perturbations would mislead the inversion and take it in the wrong direction. We demonstrate with simple synthetic examples that our method converges even when the initial velocity model is far from correct. In a companion paper, we illustrate the full potential of our method for estimating velocity anomalies under complex salt bodies. 相似文献
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Migration velocity analysis and waveform inversion 总被引：3，自引：0，他引：3
William W. Symes 《Geophysical Prospecting》2008,56(6):765-790
Least‐squares inversion of seismic reflection waveform data can reconstruct remarkably detailed models of subsurface structure and take into account essentially any physics of seismic wave propagation that can be modelled. However, the waveform inversion objective has many spurious local minima, hence convergence of descent methods (mandatory because of problem size) to useful Earth models requires accurate initial estimates of long‐scale velocity structure. Migration velocity analysis, on the other hand, is capable of correcting substantially erroneous initial estimates of velocity at long scales. Migration velocity analysis is based on prestack depth migration, which is in turn based on linearized acoustic modelling (Born or single‐scattering approximation). Two major variants of prestack depth migration, using binning of surface data and Claerbout's survey‐sinking concept respectively, are in widespread use. Each type of prestack migration produces an image volume depending on redundant parameters and supplies a condition on the image volume, which expresses consistency between data and velocity model and is hence a basis for velocity analysis. The survey‐sinking (depth‐oriented) approach to prestack migration is less subject to kinematic artefacts than is the binning‐based (surface‐oriented) approach. Because kinematic artefacts strongly violate the consistency or semblance conditions, this observation suggests that velocity analysis based on depth‐oriented prestack migration may be more appropriate in kinematically complex areas. Appropriate choice of objective (differential semblance) turns either form of migration velocity analysis into an optimization problem, for which Newton‐like methods exhibit little tendency to stagnate at nonglobal minima. The extended modelling concept links migration velocity analysis to the apparently unrelated waveform inversion approach to estimation of Earth structure: from this point of view, migration velocity analysis is a solution method for the linearized waveform inversion problem. Extended modelling also provides a basis for a nonlinear generalization of migration velocity analysis. Preliminary numerical evidence suggests a new approach to nonlinear waveform inversion, which may combine the global convergence of velocity analysis with the physical fidelity of model‐based data fitting. 相似文献
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针对鄂尔多斯盆地西缘黄土塬区复杂地表和复杂地下构造导致难以准确成像问题,采用浅层潜水波层析反演（DWT）速度建模技术,同时辅以中深层反射波层析成像技术,形成一套实用叠前深度偏移速度建模方法。首先生成一个基于钻井和解释信息的起始近地表速度,其次利用潜水波层析反演建立初始近地表模型,将其与常规处理获得的中深层速度模型进行匹配拼接,建立起初始的起伏地表全速度模型,然后在此基础上利用基于反射波的网格层析进行中深层速度建模,经过多轮次迭代,最终获得可靠的高精度速度模型。鄂尔多斯盆地西缘MJT工区地震资料的成像处理验证了这一套速度建模技术的有效性,地下构造成像更合理也更精确。 相似文献
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Quantitative imaging of complex structures from dense wide-aperture seismic data by multiscale traveltime and waveform inversions: a case study 总被引：3，自引：0，他引：3
S. Operto C. Ravaut L. Improta J. Virieux A. Herrero P. Dell'Aversana 《Geophysical Prospecting》2004,52(6):625-651
An integrated multiscale seismic imaging flow is applied to dense onshore wide‐aperture seismic data recorded in a complex geological setting (thrust belt). An initial P‐wave velocity macromodel is first developed by first‐arrival traveltime tomography. This model is used as an initial guess for subsequent full‐waveform tomography, which leads to greatly improved spatial resolution of the P‐wave velocity model. However, the application of full‐waveform tomography to the high‐frequency part of the source bandwidth is difficult, due to the non‐linearity of this kind of method. Moreover, it is computationally expensive at high frequencies since a finite‐difference method is used to model the wave propagation. Hence, full‐waveform tomography was complemented by asymptotic prestack depth migration to process the full‐source bandwidth and develop a sharp image of the short wavelengths. The final traveltime tomography model and two smoothed versions of the final full‐waveform tomography model were used as a macromodel for the prestack depth migration. In this study, wide‐aperture multifold seismic data are used. After specific preprocessing of the data, 16 frequency components ranging from 5.4 Hz to 20 Hz were inverted in cascade by the full‐waveform tomography algorithm. The full‐waveform tomography successfully imaged SW‐dipping structures previously identified as high‐resistivity bodies. The relevance of the full‐waveform tomography models is demonstrated locally by comparison with a coincident vertical seismic profiling (VSP) log available on the profile. The prestack depth‐migrated images, inferred from the traveltime, and the smoothed full‐waveform tomography macromodels are shown to be, on the whole, consistent with the final full‐waveform tomography model. A more detailed analysis, based on common‐image gather computations, and local comparison with the VSP log revealed that the most accurate migrated sections are those obtained from the full‐waveform tomography macromodels. A resolution analysis suggests that the asymptotic prestack depth migration successfully migrated the wide‐aperture components of the data, allowing medium wavelengths in addition to the short wavelengths of the structure to be imaged. The processing flow that we applied to dense wide‐aperture seismic data is shown to provide a promising approach, complementary to more classical seismic reflection data processing, to quantitative imaging of complex geological structures. 相似文献
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Common reflection surface stack using dip decomposition for rugged surface topography 总被引：1，自引：0，他引：1
We present an extension of the Common Reflection Surface （CRS） stack that provides support for an arbitrary top surface topography. CRS stacking can be applied to the original prestack data without the need for any elevation statics. The CRS-stacked zero- offset section can be corrected （redatumed） to a given planar level by kinematic wave field attributes. The seismic processing results indicate that the CRS stacked section for rugged surface topography is better than the conventional stacked section for S/N ratio and better continuity of reflection events. Considering the multiple paths of zero-offset rays, the method deals with reflection information coming from different dips and performs the stack using the method of dip decomposition, which improves the kinematic and dynamic character of CRS stacked sections. 相似文献
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Double-square-root one-way wave equation prestack tau migration in heterogeneous media 总被引：1，自引：0，他引：1
In this paper, source‐receiver migration based on the double‐square‐root one‐way wave equation is modified to operate in the two‐way vertical traveltime (τ) domain. This tau migration method includes reasonable treatment for media with lateral inhomogeneity. It is implemented by recursive wavefield extrapolation with a frequency‐wavenumber domain phase shift in a constant background medium, followed by a phase correction in the frequency‐space domain, which accommodates moderate lateral velocity variations. More advanced τ‐domain double‐square‐root wave propagators have been conceptually discussed in this paper for migration in media with stronger lateral velocity variations. To address the problems that the full 3D double‐square‐root equation prestack tau migration could meet in practical applications, we present a method for downward continuing common‐azimuth data, which is based on a stationary‐phase approximation of the full 3D migration operator in the theoretical frame of prestack tau migration of cross‐line constant offset data. Migrations of synthetic data sets show that our tau migration approach has good performance in strong contrast media. The real data example demonstrates that common‐azimuth prestack tau migration has improved the delineation of the geological structures and stratigraphic configurations in a complex fault area. Prestack tau migration has some inherent robust characteristics usually associated with prestack time migration. It follows a velocity‐independent anti‐aliasing criterion that generally leads to reduction of the computation cost for typical vertical velocity variations. Moreover, this τ‐domain source‐receiver migration method has features that could be of help to speed up the convergence of the velocity estimation. 相似文献
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In this case study we consider the seismic processing of a challenging land data set from the Arabian Peninsula. It suffers from rough top‐surface topography, a strongly varying weathering layer, and complex near‐surface geology. We aim at establishing a new seismic imaging workflow, well‐suited to these specific problems of land data processing. This workflow is based on the common‐reflection‐surface stack for topography, a generalized high‐density velocity analysis and stacking process. It is applied in a non‐interactive manner and provides an entire set of physically interpretable stacking parameters that include and complement the conventional stacking velocity. The implementation introduced combines two different approaches to topography handling to minimize the computational effort: after initial values of the stacking parameters are determined for a smoothly curved floating datum using conventional elevation statics, the final stack and also the related residual static correction are applied to the original prestack data, considering the true source and receiver elevations without the assumption of nearly vertical rays. Finally, we extrapolate all results to a chosen planar reference level using the stacking parameters. This redatuming procedure removes the influence of the rough measurement surface and provides standardized input for interpretation, tomographic velocity model determination, and post‐stack depth migration. The methodology of the residual static correction employed and the details of its application to this data example are discussed in a separate paper in this issue. In view of the complex near‐surface conditions, the imaging workflow that is conducted, i.e. stack – residual static correction – redatuming – tomographic inversion – prestack and post‐stack depth migration, leads to a significant improvement in resolution, signal‐to‐noise ratio and reflector continuity. 相似文献
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基于单程波深度延拓算法,得到震源波场在成像点的入射角度,结合对地层倾角的估计,获得入射地震波与界面法线的夹角.通过运用"保幅"的反褶积成像条件和考虑累加的炮数,解决了炮点覆盖不均匀导致的成像幅值误差问题,进而建议了炮域波动方程叠前深度偏移直接产生角道集的方法和流程.与基于空间移动或时移成像条件的波动方程叠前深度偏移提取角道集的方法相比,本文建议的方法只需少量额外的存储空间,又可补偿观测系统非均匀覆盖对成像幅值的影响;其增加的计算量与炮域偏移算法相比几乎可以忽略.文中算例表明,本文方法提取的角道集可为叠前反演提供较精确的AVO振幅特性.此外,就改善地震成像效果本身而言,提取角道集使得可在波动方程叠前深度偏移中应用剩余动校和拉伸切除技术,从而可更好地保持高频成分并提高成像的信噪比. 相似文献
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地震波的运动学信息(走时、斜率等)通常用于宏观速度建模.针对走时反演方法,一个基本问题是走时拾取或反射时差的估计.对于成像域反演方法,可以通过成像道集的剩余深度差近似计算反射波时差.在数据域中,反射地震观测数据是有限频带信号,如果不能准确地确定子波的起跳时间,难以精确地确定反射波的到达时间.另一方面,如果缺乏关于模型的先验信息,则很难精确测量自地下同一个反射界面的观测数据同相轴和模拟数据同相轴之间的时差.针对走时定义及时差测量问题,首先从叠前地震数据的稀疏表达出发,利用特征波场分解方法,提取反射子波并估计局部平面波的入射和出射射线参数.进一步,为了实现自动和稳定的走时拾取,用震相的包络极值对应的时间定义反射波的到达时,实现了立体数据中间的自动生成.理论上讲,利用包络极值定义的走时大于真实的反射波走时,除非观测信号具有无限带宽(即delta脉冲).然而,走时反演的目的是估计中-大尺度的背景速度结构,因此走时误差导致的速度误差仍然在可以接受的误差范围内.利用局部化传播算子及特征波聚焦成像条件将特征波数据直接投影到地下虚拟反射点,提出了一种新的反射时差估计方法.既避免了周期跳跃现象以及串层等可能性,又消除了振幅因素对时差测量的影响.最后,在上述工作基础之上,提出了一种基于特征波场分解的新型全自动反射走时反演方法(CWRTI).通过对泛函梯度的线性化近似,并用全变差正则化方法提取梯度的低波数部分,实现了背景速度迭代反演.在理论上,无需长偏移距观测数据或低频信息、对初始模型依赖性低且计算效率高,可以为后续的全波形反演提供可靠的初始速度模型.理论和实际资料的测试结果证明了本文方法的有效性. 相似文献
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An imaging technique is developed which exceeds the resolution limitation prescribed by conventional seismic imaging methods. The high‐resolution imaging is obtained by introducing a sparseness‐constrained least‐squares inversion into the imaging process of prestack depth migration. This is implemented by a proposed interference technique. In contrast to conventional depth migration, a decomposed signal or combined event, instead of the source wavelet, is needed in the proposed scheme. The proposed method aims to image a small local region with a higher resolution using the prestack data set. It should be applied following conventional depth imaging if a higher resolution is needed in a target zone rather than replacing the conventional depth imaging for the entire medium. Synthetic examples demonstrate the significant improvements in the resolution using the proposed scheme. 相似文献
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描述地震波衰减特征的品质因子Q对地震数据处理和油藏描述非常重要,在地震勘探领域,Q值一般通过垂直地震剖面(VSP)数据或地面地震数据得到.由于叠前地面地震数据具有复杂的射线路径且存在噪声、调谐干涉效应等影响,从叠前地震数据中准确估计Q值相对困难.本文以地震波射线传播为基础,根据同相轴局部斜率和射线参数的映射关系,将多射线波形频谱同时带入谱比法联合反演估计Q值,提出了基于多射线联合反演的速度无关叠前Q值估计方法.该方法通过局部斜率属性避开了速度对Q值估计的影响,局部斜率携带地震波传播的速度信息,具有相同局部斜率的地震反射波具有相同的传播射线参数.同相轴局部斜率是地震数据域的属性,而速度是模型域的参数,在估计Q值中采用数据域的属性参数可以直接应用于数据的联合反演,而不需要通过速度对其做进一步的转化,从而提高了Q值估计的精度.同时,本方法采用预测映射(predictive mapping)技术将非零炮检距反射信息映射到零炮检距处,从而获得零偏移距走时对应的Q值.模拟和实际算例验证了本文方法的有效性. 相似文献
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本文提出了一套叠前地震数据稀疏表达(特征波场合成)、深度偏移成像和层析成像的处理流程.不同于传统的变换域中的数据稀疏表达理论,本文利用局部平面波的传播方向(慢度矢量),在中心炮检点处同时进行波束合成,从而将地震数据投影到局部平面波域(高维空间)中.由于波束合成后的地震数据描述了局部平面波的方向特征,因此称之为特征波场.然而波束合成算法需要估计局部平面波的慢度矢量.当地震数据受噪声干扰时,难以在常规τ-p谱中自动估计局部平面波的射线参数(慢度矢量).本文提出了基于反演理论的特征波场合成方法,可以同时反演局部平面波及其传播方向,从而提高特征波合成的自动化程度并保持方法的稳健性.通过特征波场合成,可以将地震数据分解为单独的震相(波形).这样的数据可以直接用来成像及反演.在局部平面波域中,由于局部平面波的入射与出射射线参数已知,传统的Kirchhoff叠前深度偏移(PSDM)和高斯束/控制束PSDM可以实现从"沿等时面的画弧"到"向反射点(段)的直接投影"的转变,叠前偏移的效率以及成像质量可以同时提高.此外,特征波场与地下反射点(段)的一对一映射关系使得叠前深度偏移与层析成像融为一体,可以极大地提高速度反演的效率.数值试验证明了特征波场合成、叠前深度成像以及层析反演的有效性. 相似文献
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Pre-stack depth migration velocity analysis is one of the key techniques influencing image quality. As for areas with a rugged surface and complex subsurface, conventional prestack depth migration velocity analysis corrects the rugged surface to a known datum or designed surface velocity model on which to perform migration and update the velocity. We propose a rugged surface tomographic velocity inversion method based on angle-domain common image gathers by which the velocity field can be updated directly from the rugged surface without static correction for pre-stack data and improve inversion precision and efficiency. First, we introduce a method to acquire angle-domain common image gathers (ADCIGs) in rugged surface areas and then perform rugged surface tomographic velocity inversion. Tests with model and field data prove the method to be correct and effective. 相似文献
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Elastic full waveform inversion of seismic reflection data represents a data‐driven form of analysis leading to quantification of sub‐surface parameters in depth. In previous studies attention has been given to P‐wave data recorded in the marine environment, using either acoustic or elastic inversion schemes. In this paper we exploit both P‐waves and mode‐converted S‐waves in the marine environment in the inversion for both P‐ and S‐wave velocities by using wide‐angle, multi‐component, ocean‐bottom cable seismic data. An elastic waveform inversion scheme operating in the time domain was used, allowing accurate modelling of the full wavefield, including the elastic amplitude variation with offset response of reflected arrivals and mode‐converted events. A series of one‐ and two‐dimensional synthetic examples are presented, demonstrating the ability to invert for and thereby to quantify both P‐ and S‐wave velocities for different velocity models. In particular, for more realistic low velocity models, including a typically soft seabed, an effective strategy for inversion is proposed to exploit both P‐ and mode‐converted PS‐waves. Whilst P‐wave events are exploited for inversion for P‐wave velocity, examples show the contribution of both P‐ and PS‐waves to the successful recovery of S‐wave velocity. 相似文献
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变阻尼约束层析成像及其在VSP资料中的应用(英文) 总被引：1，自引：0，他引：1
初至波走时层析成像已经取得了广泛的应用,然而,由于观测系统的限制,射线在模型中分布不均匀,导致层析结果的分辨能力不足。变阻尼约束方法应用不均匀的先验信息来匹配不均匀的数据分布,可以减小速度模型校正量与射线覆盖程度的相关性。本文将变阻尼约束方法应用于初至波旅行时层析成像中,并将平滑约束方法加入正则化方程组中来避免单独使用变阻尼约束带来的不稳定性,利用阿尔法滤波器对反演中间迭代结果进行平滑和去噪,采用LSQR算法求解线性方程组来提高收敛速度和压制误差传递。本文应用上述层析成像算法对VSP观测系统进行速度反演,分别应用于检测板速度模型数据和实际VSP资料速度反演中,结果表咀变阻尼约束层析成像可以改善射线不均匀覆盖带来的影响,从而提高速度反演结果的质量;VSP资料检波点附近的速度反演结果可靠性高。 相似文献
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偏移成像是VSP数据处理中的一个重要环节,常规的VSP成像方法通常利用VSP-CDP转换或Kirchhoff偏移,均存在保幅性差及成像精度低等问题,而波动方程叠前深度偏移被认为是对地下复杂构造进行成像的精确偏移方法.任意广角波动方程作为一种高精度的空间域单程波波动方程,同时由于只含有二阶偏导数项,易于数值实现,与其他单程波波动方程相比,具有更大的成像倾角,因此是偏移成像的有力工具之一.本文将AWWE推广应用到VSP数据成像中,实现了VSP时空域高角度单程波方程偏移.首先从三维标量任意广角波动方程出发,推导了完全匹配层吸收边界条件,在基本不增加计算量的前提下有效地压制了边界反射成像噪音,同时利用非线性反演算法优选参考速度来提高平方根算子的近似程度,从而提高高角度地层的成像精度.模型数值模拟实验验证了该方法的有效性,同时表明该方法在陡倾角构造情况下能取得很好的成像效果.最后对某地区实际观测的VSP资料进行了偏移成像,并与地面地震偏移结果进行了对比,显示出VSP波动方程偏移在成像分辨率上的优势. 相似文献
20.
J.F.B. Bolte 《Geophysical Prospecting》2004,52(6):523-534
The common focal point (CFP) method and the common reflection surface (CRS) stack method are compared. The CRS method is a fast, highly automated procedure that provides high S/N ratio simulation of zero‐offset (ZO) images by combining, per image point, the reflection energy of an arc segment that is tangential to the reflector. It uses smooth parametrized two‐way stacking operators, based on a data‐driven triplet of attributes in 2D (eight parameters in 3D). As a spin‐off, the attributes can be used for several applications, such as the determination of the geometrical spreading factor, multiple prediction, and tomographic inversion into a smooth background velocity model. The CFP method aims at decomposing two‐way seismic reflection data into two full‐aperture one‐way propagation operators. By applying an iterative updating procedure in a half‐migrated domain, it provides non‐smooth focusing operators for prestack imaging using only the energy from one focal point at the reflector. The data‐driven operators inhibit all propagation effects of the overburden. The CFP method provides several spin‐offs, amongst which is the CFP matrix related to one focal point, which displays the reflection amplitudes as measured at the surface for each source–receiver pair. The CFP matrix can be used to determine the specular reflection source–receiver pairs and the Fresnel zone at the surface for reflection in one single focal point. Other spin‐offs are the prediction of internal multiples, the determination of reflectivity effects, velocity‐independent redatuming and tomographic inversion to obtain a velocity–depth model. The CFP method is less fast and less automated than the CRS method. From a pointwise comparison of features it is concluded that one method is not a subset of the other, but that both methods can be regarded as being to some extent complementary. 相似文献