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1.
The key processes in marine seismic imaging include (i) removing from seismic data all seismic events (free-surface multiples and ghosts) which contain at least one reflection at the sea surface in their wave-propagation path, and leaving those with no reflection at the free surface (internal multiples and primaries), (ii) removing events with at least two reflections in the subsurface (internal multiples), and leaving events with only one reflection in the subsurface (primaries), and then (iii) locating the scattering points and reflectors inside the subsurface which are the sources of primaries and internal multiple events. All these processes are here explained, derived, and optimized via scattering diagrams (diagrammatica) in a way similar to the way the quantum field theory is often explained via Feynman diagrams. Our discussion of the removal of events with free-surface reflections from the data will be brief, as the diagrammatica of these events are now well understood.The main focus of this paper is the diagrammatica of internal multiples and primaries. Although these events do not contain any reflection at the sea surface, it is important to reconstruct them with scattering points near the sea surface, where seismic data are recorded. So our diagrammatica of primaries and internal multiples include events which are not directly recorded in seismic data but which can be constructed from seismic data. These events have allowed us to construct scattering diagrams of primaries and internal multiples with scattering points near the sea surface. Furthermore, these new diagrammatica of internal multiples and primaries can be used to remove internal multiples from the data. 相似文献
2.
The filter for wave-equation-based water-layer multiple suppression, developed by the authors in the x-t, the linear τ-p, and the f-k domains, is extended to the parabolic τ-2 domain. The multiple reject areas are determined automatically by comparing the energy on traces of the multiple model (which are generated by a wave-extrapolation method from the original data) and the original input data (multiples + primaries) in τ-p space. The advantage of applying the data-adaptive 2D demultiple filter in the parabolic τ-p domain is that the waves are well separated in this domain. The numerical examples demonstrate the effectiveness of such a dereverberation procedure. Filtering of multiples in the parabolic τ-p domain works on both the far-offset and the near-offset traces, while the filtering of multiples in the f-k domain is effective only for the far-offset traces. Tests on a synthetic common-shot-point (CSP) gather show that the demultiple filter is relatively immune to slight errors in the water velocity and water depth which cause arrival time errors of the multiples in the multiple model traces of less than the time dimension (about one quarter of the wavelet length) of the energy summation window of the filter. The multiples in the predicted multiple model traces do not have to be exact replicas of the multiples in the input data, in both a wavelet-shape and traveltime sense. The demultiple filter also works reasonably well for input data contaminated by up to 25% of random noise. A shallow water CSP seismic gather, acquired on the North West Shelf of Australia, demonstrates the effectiveness of the technique on real data. 相似文献
3.
For data acquired with conventional acquisition techniques, surface multiples are usually considered as noise events that obscure the primaries. However, in this paper we demonstrate that for the situation of blended acquisition, meaning that different sources are shooting in a time‐overlapping fashion, multiples can be used to ‘deblend’ the seismic measurements. We utilize the recently introduced estimation of primaries by sparse inversion (EPSI) methodology, in which the primary impulse responses are considered to be the unknowns in a large‐scale inversion process. With some modifications the estimation of primaries by sparse inversion method can be used for blended seismic data. As output this process gives unblended primary impulse responses with point sources and receivers at the surface, which can be used directly in traditional imaging schemes. It turns out that extra information is needed to improve on the deblending of events that do not have much associated multiple energy in the data, such as steep events at large offsets. We demonstrate that this information can be brought in during acquisition and during processing. The methodology is illustrated on 2D synthetic data. 相似文献
4.
提出一种基于Radon 变换和正交多项式变换的多方向正交多项式变换压制多次波方法.抛物Radon变换对不同曲率方向的同相轴叠加,根据速度差异区分一次波和多次波,但Radon反变换会损伤振幅特性,不利于AVO分析.多方向正交多项式变换在Radon变换(某一曲率方向的零阶特性)的基础上,利用正交多项式变换进一步分析同相轴的高阶多项式分布特性,用正交多项式谱表征同相轴AVO特性;根据一次波和多次波速度差异和同相轴能量分布特征实现多次波压制.该方法的优点是仅用一个曲率参数就可描述同相轴剩余时差参数,提高了一次波和多次波的剩余时差分辨率.实验结果表明,该方法可以有效压制多次波并保留一次波AVO特性. 相似文献
5.
在浅水情况下，由于观测数据中缺少近偏移距信息，水层多次波的压制面临挑战.利用多道预测算子压制水层多次波是浅水环境下压制多次波的重要方法之一，这种方法先从输入数据中估计出多道预测算子，再将预测算子和输入数据做褶积预测出水层相关多次波.然而，估计的多道预测算子很容易受噪声污染，从而影响多次波模型的精度.所以，我们提出了改进的多道预测算子压制浅水多次波方法.该方法先从数据中估计出多道预测算子，并利用估计的算子构建出精确的水层模型；然后，通过计算算子的走时信息、估计振幅信息、合成新算子三个步骤来修正原始的多道预测算子.修正的算子不仅不受噪声影响，还含有精确的走时信息、可靠的振幅信息；最后，该方法用修正的算子来预测多次波，并结合自适应相减，将预测的多次波从输入数据中去除.通过合成数据和实际资料的验证表明，相比于原始的多道预测算子压制多次波方法，改进的方法能够取得更好的压制效果. 相似文献
6.
在常规地震资料处理中,多次反射波被视为噪声并从地震数据中去除,以免在之后的地震资料解释中造成误解.而事实上,多次波也是地震信号,是照明波场的一部分,能够对地下构造成像的精度做出贡献.本文分析了多次波在传统单程波叠前深度偏移中产生构造假象的机制和表现,为实现基于单程波偏移算子的多次波成像,修改了单程波叠前深度偏移的边界条件,即将输入的震源波场用包含多次波的记录来替代,输入的记录波场用预测出的表层相关多次波来替代,实现了基于单程波偏移算子的地表相关多次波成像,并从理论上给出了其成像依据.通过基于二范式最小能量差原则求取的匹配因子,将多次波成像结果与一次波成像结果进行匹配叠加,应用多次波成像来弥补一次波成像的不足.简单模型验证了基于单程波偏移算子的多次波成像方法的有效性,最后对Sigsbee2B模型进行了一次波与多次波联合成像试算,盐边界高陡构造成像质量得到了明显改善. 相似文献
7.
在常规偏移方法中一般都需要压制地震数据中的多次波,仅利用一次波信息成像,把自由表面反射的多次波视为噪声,但是在多次波中也包含着地下结构信息,应该将其充分利用到成像中来.事实上,已经有不少成像方法试图利用多次波信息,但是大部分方法都需要对多次波进行预测.本文提出了基于傅里叶有限差分偏移算子的数据自相关偏移方法.在这种偏移方法中,对含有一次波和多次波的地震数据,分别进行下行和上行延拓,然后直接利用常规的互相关成像条件成像.由于波场延拓采用了傅里叶有限差分算子,其计算效率高,能够很好地对复杂介质中的地震数据进行延拓.在数值试验中,使用了一个含散射点的三层模型和Marmousi模型.合成数据测试结果表明,这种方法可以对更大范围的地下构造成像,比常规的只利用一次波的傅里叶有限差分法照明度更好,并且在浅层可以提供更高的分辨率.我们提出的数据自相关策略易于实现且避免了繁杂的多次波预测,这对于复杂地下构造成像可能有着重大意义. 相似文献
8.
地震资料含有各种类型多次波，而传统成像方法仅利用地震一次反射波成像，在地震成像前需将多次波去除.然而，多次波携带了丰富的地下结构信息，多次波偏移能够提供除反射波外的额外地下照明.修改传统逆时偏移方法，用包含一次反射波和多次波的原始记录代替震源子波，将SRME方法预测的表面多次波代替一次反射波作为输入数据，可将表面多次波成像.多次波成像的挑战和困难在于大量串扰噪声的产生，针对表面多次波成像中的成像噪声问题，将最小二乘逆时偏移方法与多次波分阶思想结合起来，发展可控阶数的表面多次波反演成像方法，有望初步实现高精度的表面多次波成像.在消除原始记录中的表面多次波后，通过逆散射级数方法预测得到层间多次波，将层间多次波作为逆时偏移方法的输入数据可将其准确归位到地下反射位置.数值实验表明，多次波成像能够有效地为地下提供额外照明，而可控阶表面多次波最小二乘逆时偏移成像方法几乎完全避免成像噪声. 相似文献
9.
常规虚源点Marchenko自聚焦多次波预测方法只适用于预测不含自由表面的多次波模型,局限于压制层间多次波,该方法在构建上下行格林函数场前,必须从反射响应中去除所有与表面相关的多次波.本文对构建上下行Marchenko格林函数方程进行改进,得到了包含一次波、层间多次波和自由表面多次波的格林函数,利用改进的Marchenko自聚焦预测方法预测自由表面多次波.本文利用水平层状模型数据及SMARRT模型数据证明,改进后的Marchenko法预测海底相关的自由表面多次波效果较为理想,该方法避免了常规SRME自由表面多次波预测方法需要近道重构的缺陷,能够有效提高地震资料的信噪比和分辨率. 相似文献
10.
自由表面多次波压制是海底地震仪（Ocean Bottom Seismometer,OBS）数据处理和成像中的难点,OBS数据多次波能量强,周期长,严重影响深层一次反射波的处理和成像.不同于常规拖缆观测系统,OBS数据站点一般相隔较远,仅仅利用检波点稀疏的波场信息难以压制OBS数据中的自由表面多次波.本文采用拖缆数据与OBS数据联合,利用稀疏反演估计（Estimation of Primaries and Multiples by Sparse Inversion,EPSI）方法,研究了OBS数据自由表面多次波压制理论,分析了OBS多次波产生的机理,详细推导了拖缆数据与OBS数据联合预测OBS多次波的EPSI方法基本原理.通过利用拖缆数据的信息,实现了OBS检波点稀疏数据多次波的压制问题.EPSI方法通过稀疏反演直接估计一次反射波,避免了SRME（Surface Related Multiple Elimination）方法中自适应相减对有效信号的损害,保真了一次反射有效信号,理论模拟OBS数据验证了方法的有效性. 相似文献
11.
Passive seismic has recently attracted a great deal of attention because non‐artificial source is used in subsurface imaging. The utilization of passive source is low cost compared with artificial‐source exploration. In general, constructing virtual shot gathers by using cross‐correlation is a preliminary step in passive seismic data processing, which provides the basis for applying conventional seismic processing methods. However, the subsurface structure is not uniformly illuminated by passive sources, which leads to that the ray path of passive seismic does not fit the hyperbolic hypothesis. Thereby, travel time is incorrect in the virtual shot gathers. Besides, the cross‐correlation results are contaminated by incoherent noise since the passive sources are always natural. Such noise is kinematically similar to seismic events and challenging to be attenuated, which will inevitably reduce the accuracy in the subsequent process. Although primary estimation for transient‐source seismic data has already been proposed, it is not feasible to noise‐source seismic data due to the incoherent noise. To overcome the above problems, we proposed to combine focal transform and local similarity into a highly integrated operator and then added it into the closed‐loop surface‐related multiple elimination based on the 3D L1‐norm sparse inversion framework. Results proved that the method was capable of reliably estimating noise‐free primaries and correcting travel time at far offsets for a foresaid virtual shot gathers in a simultaneous closed‐loop inversion manner. 相似文献
12.
Antoine Guitton 《Geophysical Prospecting》2006,54(2):135-152
Surface‐related multiples are attenuated for one sail line and one streamer of a 3D data set (courtesy of Compagnie Générale de Géophysique). The survey was carried out in the Gulf of Mexico in the Green Canyon area where salt intrusions close to the water‐bottom are present. Because of the complexity of the subsurface, a wavefield method incorporating the full 3D volume of the data for multiple removal is necessary. This method comprises modelling of the multiples, where the data are used as a prediction operator, and a subtraction step, where the model of the multiples is adaptively removed from the data with matching filters. The accuracy of the multiple model depends on the source/receiver coverage at the surface. When this coverage is not dense enough, the multiple model contains errors that make successful subtraction more difficult. In these circumstances, one can either (1) improve the modelling step by interpolating the missing traces, (2) improve the subtraction step by designing methods that are less sensitive to modelling errors, or (3) both. For this data set, the second option is investigated by predicting the multiples in a 2D sense (as opposed to 3D) and performing the subtraction with a pattern‐based approach. Because some traces and shots are missing for the 2D prediction, the data are interpolated in the in‐line direction using a hyperbolic Radon transform with and without sparseness constraints. The interpolation with a sparseness constraint yields the best multiple model. For the subtraction, the pattern‐based technique is compared with a more standard, adaptive‐subtraction scheme. The pattern‐based approach is based on the estimation of 3D prediction‐error filters for the primaries and the multiples, followed by a least‐squares estimation of the primaries. Both methods are compared before and after prestack depth migration. These results suggest that, when the multiple model is not accurate, the pattern‐based method is more effective than adaptive subtraction at removing surface‐related multiples while preserving the primaries. 相似文献
13.
《中国科学:地球科学(英文版)》2015,(3)
The South China Sea where water depth is up to 5000 m is the most promising oil and gas exploration area in China in the future.The seismic data acquired in the South China Sea contain various types of multiples that need to be removed before imaging can be developed.However,compared with the conventional reflection migration,multiples carry more information of the underground structure that helps provide better subsurface imaging.This paper presents a method to modify the conventional reverse time migration so that multiple reflections can migrate to their correct locations in the subsurface.This approach replaces the numerical impulsive source with the recorded data including primaries and multiples on the surface,and replaces the recorded primary reflection data with multiples.In the reverse time migration process,multiples recorded on the surface are extrapolated backward in time to each depth level,while primaries and multiples recorded on the surface are extrapolated forward in time to the same depth levels.By matching the difference between the primary and multiple images using an objective function,this algorithm improves the primary resultant image.Synthetic tests on Sigsbee2 B show that the proposed method can obtain a greater range and better underground illumination.Images of deep water in the South China Sea are obtained using multiples and their matching with primaries.They demonstrate that multiples can make up for the reflection illumination and the migration of multiples is an important research direction in the future. 相似文献
14.
地震数据中发育的层间多次波是影响速度分析和偏移成像的精度和可靠性的关键.通常情况下，层间多次波的动校正量、叠加速度和频率与一次波并无明显差异，从而对识别、预测和压制多次波带来了极大挑战.传统虚同相轴方法基于物理图像和定性公式，其预测的层间多次波振幅和相位精度难以满足实际需求，造成了其对匹配算法的过度依赖.本文针对传统虚同相轴方法的理论缺陷和计算精度问题，通过理论推导得到了新的自适应虚同相轴方法.相比于传统方法，自适应虚同相轴方法能够显著提高压制多次波能力，同时减少对匹配算法的依赖.本文给出了自适应虚同相轴方法的推导过程，并运用一维和二维模型算例验证了方法相较于传统虚同相轴方法的多次波预测精度优势.通过在PLUTO模型和实际陆地地震数据上的应用实例，证明了本文新研究的自适应虚同相轴方法对去除层间多次波，恢复并突出目标储层同相轴，提高地震成像分辨率的显著作用. 相似文献
15.
海水与空气间的强波阻抗差使得海洋地震资料普遍发育自由表面相关多次波,如何利用好多次波所携带的有效信息已成为提高海洋地震资料成像品质的新突破点.基于面炮偏移的一次波与多次波同时成像方法能够避免多次波预测精度的影响,但是,正向传播的震源子波与反向延拓的自由表面相关多次波所产生的干涉假象严重制约了该技术的应用,本文提出了一种基于单程波偏移算子,可在成像域压制干涉假象的一次波与多次波同时成像方法.其中包含了三个步骤:第一,传统单程波偏移成像方法中的震源子波替换为一次波、多次波与震源子波,初始上行延拓波场为一次波与多次波,基于单程波算子的波场延拓与互相关成像条件的应用得到包含干涉假象的一次波与多次波同时成像;第二,以子波为震源,自由表面相关多次波为记录,按照传统单程波偏移成像方法得到干涉假象;第三,基于最小二乘匹配滤波算法,将第一步的成像结果与第二步的干涉假象进行匹配相减,得到干涉假象衰减后的一次波与多次波同时成像,避开了由于实际资料子波无法准确提取而造成一次波与多次波对成像能量级的不一致性.Sigsbee2B模型测试验证了本方法的有效性,并在我国某探区深海实际资料处理中得到了成功应用,深层基底得到了清晰刻画,并且照明均衡度明显改善. 相似文献
16.
A strategy for multiple removal consists of estimating a model of the multiples and then adaptively subtracting this model from the data by estimating shaping filters. A possible and efficient way of computing these filters is by minimizing the difference or misfit between the input data and the filtered multiples in a least‐squares sense. Therefore, the signal is assumed to have minimum energy and to be orthogonal to the noise. Some problems arise when these conditions are not met. For instance, for strong primaries with weak multiples, we might fit the multiple model to the signal (primaries) and not to the noise (multiples). Consequently, when the signal does not exhibit minimum energy, we propose using the L1‐norm, as opposed to the L2‐norm, for the filter estimation step. This choice comes from the well‐known fact that the L1‐norm is robust to ‘large’ amplitude differences when measuring data misfit. The L1‐norm is approximated by a hybrid L1/L2‐norm minimized with an iteratively reweighted least‐squares (IRLS) method. The hybrid norm is obtained by applying a simple weight to the data residual. This technique is an excellent approximation to the L1‐norm. We illustrate our method with synthetic and field data where internal multiples are attenuated. We show that the L1‐norm leads to much improved attenuation of the multiples when the minimum energy assumption is violated. In particular, the multiple model is fitted to the multiples in the data only, while preserving the primaries. 相似文献
17.
A.J. Berkhout 《Geophysical Prospecting》2017,65(1):106-145
Surface removal and internal multiple removal are explained by recursively separating the primary and multiple responses at each depth level with the aid of wavefield prediction error filtering. This causal removal process is referred to as “data linearization.” The linearized output (primaries only) is suitable for linear migration algorithms. Next, a summary is given on the migration of full wavefields (primaries + multiples) by using the concept of secondary sources in each subsurface gridpoint. These secondary sources are two‐way and contain the gridpoint reflection and the gridpoint transmission properties. In full wavefield migration, a local inversion process replaces the traditional linear imaging conditions. Finally, Marchenko redatuming is explained by iteratively separating the full wavefield response from above a new datum and the full wavefield response from below a new datum. The redatuming output is available for linear migration (Marchenko imaging) or, even better, for full wavefield migration. Linear migration, full wavefield migration, and Marchenko imaging are compared with each other. The principal conclusion of this essay is that multiples should not be removed, but they should be utilized, yielding two major advantages: (i) illumination is enhanced, particularly in the situation of low signal‐to‐noise primaries; and (ii) both the upper side and the lower side of reflectors are imaged. It is also concluded that multiple scattering algorithms are more transparent if they are formulated in a recursive depth manner. In addition to transparency, a recursive depth algorithm has the flexibility to enrich the imaging process by inserting prior geological knowledge or by removing numerical artefacts at each depth level. Finally, it is concluded that nonlinear migration algorithms must have a closed‐loop architecture to allow successful imaging of incomplete seismic data volumes (reality of field data). 相似文献
18.
Progress in the imaging of the mantle and core is partially limited by the sparse distribution of natural sources; the earthquake hypocenters are mainly along the active lithospheric plate boundaries. This problem can be approached with seismic interferometry. In recent years, there has been considerable progress in the development of seismic interferometric techniques. The term seismic interferometry refers to the principle of generating new seismic responses by cross‐correlating seismic observations at different receiver locations. The application of interferometric techniques on a global scale could create sources at locations where no earthquakes occur. In this way, yet unknown responses would become available for the application of travel‐time tomography and surface‐wave dispersion studies. The retrieval of a dense‐enough sampling of source gathers would largely benefit the application of reflection imaging. We derive new elastodynamic representation integrals for global‐scale seismic interferometry. The relations are different from other seismic interferometry relations for transient sources, in the sense that they are suited for a rotating closed system like the Earth. We use a correlation of an observed response with a response to which free‐surface multiple elimination has been applied to account for the closed system. Despite the fact that the rotation of the Earth breaks source‐receiver reciprocity, the seismic interferometry relations are shown to be valid. The Coriolis force is included without the need to evaluate an extra term. We synthesize global‐scale earthquake responses and use them to illustrate the acoustic versions of the new interferometric relations. When the sampling of real source locations is dense enough, then both the responses with and without free‐surface multiples are retrieved. When we do not take into account the responses from the sources in the direct neighborhood of the seismic interferometry‐constructed source location, the response with free‐surface multiples can still be retrieved. Even when only responses from sources at a certain range of epicentral distances are available, some events in the Green's function between two receiver locations can still be retrieved. The retrieved responses are not perfect, but the artefacts can largely be ascribed to numerical errors. The reconstruction of internal events – the response as if there was a source and a receiver on (major) contrasts within the model – could possibly be of use for imaging. With modelling it is possible to discover in which region of the correlation panel stationary phases occur that contribute to the retrieval of events. This knowledge opens up a new way of filtering out undesired events and of discovering whether specific events could be retrieved with a given source‐receiver configuration. 相似文献
19.
本文将多次波自适应相减问题表示为一个多道卷积信号的盲分离问题.利用2D卷积核来表示预测多次波和实际多次波之间的差异,并采用分离出的一次波信号的非高斯性最大化作为优化目标,我们提出一种基于多道卷积信号盲分离的多次波自适应相减算法.为了求解上述非线性优化问题,所提方法将其转化为一个迭代线性优化问题,采用迭代最小二乘方法加以实现.由于采用了多道卷积信号盲分离模型,所提方法能够适应预测和真实多次波之间在时间及空间上的变化.通过对简单模型数据、Pluto数据和实际数据进行处理,验证了所提算法的有效性. 相似文献
20.
Short-period multiple reflections pose a particular problem in the North Sea where predictive deconvolution is often only partially successful. The targeted multiple attenuation (TMA) algorithm comprises computation of the covariance matrix of preflattened prestack or post-stack seismic data, the determination of the dominating eigenvectors of the covariance matrix, and subtraction of the related eigenimages followed by reverse flattening. The main assumption made is that the flattened multiple reflections may be represented by the first eigenimage(s) which implies that the spatial amplitude variations of primaries and associated multiples are similar. This assumption usually limits the method to short-period multiple reflections. TMA is applicable post-stack or prestack to common-offset gathers. It is computationally fast, robust towards random noise, irregular geometry and spatial aliasing, and it preserves the amplitudes of primaries provided they are not parallel to the targeted multiples. Application of TMA to 3D wavefields is preferable because this allows a better discrimination between primaries and multiples. Real data examples show that the danger of partially removing primary energy can be reduced by improving the raw multiple model that is based on eigenimages, for example by prediction filtering. 相似文献