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1.
F. AMINZADEH 《Geophysical Prospecting》1989,37(8):893-906
Data from offshore Norway is used to study applications of elastic VSP modelling in detecting shear waves and observing the effects of successive mode conversion in field-recorded VSP data. The shear-wave velocities and densities from log data are used in conjunction with compressional wave velocities determined from surface seismic and log data in the VSP modelling. The time domain non-normal incidence elastic VSP modelling technique of Aminzadeh and Mendel is used as the modelling algorithm. Two surface seismograms are computed first. One is the vertical component and the other is the horizontal component for plane waves that have specified incident angles. A downward continuation method is then applied to generate seismograms at different depth points. The collection of these seismograms constitutes non-normal incidence VSPs. Both vertical and horizontal components of VSP data can be obtained by this procedure. In this paper non-normal incidence VSPs are generated for a 12.5° incident plane wave. The modelling results of layered earth systems of thin layers and thick layers are both compared with field data, and the effect of mode conversions in thin layers is observed. Several events in the field data can be explained by this elastic VSP modelling. Comparison of the model data and field data enabled a probable tube wave or out-of-plane event to be identified, the removal of which significantly improved the final VSP section. This study also shows how the VSP data helped the interpretation of the surface 3D 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.
海洋地震资料普遍发育强能量表面多次波,传统表面多次波压制技术（SRME）能够预测出所有阶次表面多次波,但是各阶次表面多次波相互混叠。为了能够单独利用不同阶次的表面多次波成像,降低干涉假象对多次波成像的影响,需要将不同阶次的表面多次波分离出来。本文提出一种基于扩展SRME的海洋单阶次表面多次波分离方法。首先,应用SRME技术预测出混叠的所有表面多次波;其次,修改常规SRME技术的边界输入条件,将上一步求得的所有多次波进行升阶次处理;再次,预测出混叠的所有表面多次波与其升阶次后的表面多次波匹配相减求得单阶次多次波。以此类推,能够逐步分离出不同阶次的表面多次波。数值模型和某深海实际资料测试表明本方法的有效性,不同阶次表面多次波被有效分离,为后期多次波的利用奠定了基础。 相似文献
4.
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
5.
本文深入分析了多次波逆时偏移的成像原理和串扰假象产生机制,并提出了多次波分阶逆时偏移策略,即首先应用自由界面多次波衰减方法对原始炮集记录中的多次波进行剔除得到一次波记录,然后应用一次波记录预测获得各阶多次波记录,最后将各阶多次波记录分别进行逆时偏移成像.模型实验结果表明,多次波分阶逆时偏移其各阶多次波成像剖面均可对真实界面正确成像且其能够有效压制串扰假象,其中一阶多次波逆时偏移剖面的成像精度最高,其深层成像质量明显优于常规多次波逆时偏移. 相似文献
6.
This paper is directed at modeling layered media. We extend the plane-wave normal-incidence state-space model developed by Mendel, Nahi and Chan in 1979, to the non-normal incidence case. To do this we introduce a shifting principle, a zero-offset wavefront, and zero-offset travel times for different layers. We also develop an algorithm for obtaining a synthetic line source reflection seismogram. In this algorithm non-normal incidence plane-wave seismograms are summed over a range of incident angles. The algorithm is based on a modified version of Sommerfield's (1896) theorem. Simulations of acoustic and elastic media are included which illustrate the applicability of our plane-wave and line source seismograms for both elastic and acoustic cases. 相似文献
7.
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
8.
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
9.
M.T. TANER 《Geophysical Prospecting》1980,28(1):30-48
Multiple sea-floor reflections in deep water often are not effectively suppressed by either CDP stacking nor standard predictive deconvolution methods. These methods fail because the reflection coefficient varies markedly with angle of incidence and also because of the variation of arrival time with offset and because of dip. For a reasonablly flat sea-floor, multiples of various orders and the primary sea-floor reflection which have all been reflected at nearly the same angle lie along a straight line through the origin in time-offset space. This line is called the “radial direction.” The multiples which lie along this line show a systematic relationship because they all experience the same water-bottom reflection effect. In other words, multiples behave in a stationary manner along the radial directions on multi-trace seismic records. A technique of multi-channel predictive deconvolution, called “Radial Multiple Suppression,” utilizes this aspect to design Wiener operators for the prediciton and suppression of water bottom multiples. The effectiveness of the technique is demonstrated by the study of field records, autocorrelations, velocity analyses, and stacked sections before and after Radial Multiple Suppression processing. 相似文献
10.
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
11.
Field‐survey characteristics can have an important impact on the quality of multiples predicted by surface‐related multiple elimination (SRME) algorithms. This paperexamines the effects of three particular characteristics: in‐line spatial sampling, source stability, and cable feathering. Inadequate spatial sampling causes aliasing artefacts. These can be reduced by f–k filtering at the expense of limiting the bandwidth in the predicted multiples. Source‐signature variations create artefacts in predicted multiples due to spatial discontinuities. Variations from a well‐behaved airgun array produced artefacts having an rms amplitude about 26 dB below the rms amplitude of multiples predicted with no variations. Cable feathering has a large impact on the timingerrors in multiples predicted by 2D SRME when it is applied in areas having cross dip. All these problems can be reduced by a combination of better survey design, use of advanced data‐acquisition technologies, and additional data‐processing steps. 相似文献
12.
使用相同的炮记录,多次波偏移能提供比反射波偏移更广的地下照明和更多的地下覆盖但是同时产生很多的串声噪声.相比传统逆时偏移,最小二乘逆时偏移反演的反射波成像结果具有更高的分辨率和更均衡的振幅.我们主要利用最小二乘逆时偏移压制多次波偏移产生的串声噪声.多次波最小二乘逆时偏移通常需要一定的迭代次数以较好地消除串声噪声.若提前将一阶多次波从所有阶数的多次波中过滤出来,使用相同的迭代次数,一阶多次波的最小二乘逆时偏移能够得到具有更高信噪比的成像剖面,而且能够提供与多次波最小二乘逆时偏移相似的有效地下结构成像. 相似文献
13.
地震数据采集过程中,受野外施工条件的制约,往往很难获得完整的地震波场,尤其近炮检距数据的缺失尤为严重.当前,很多地震数据处理方法的应用都依赖于近炮检距数据,如何对近炮检距的缺失数据进行重建,是一个重要的研究课题.本文通过多次波和一次波的互相关构建虚拟一次波,利用数据本身的波场信息,对缺失的近炮检距数据进行插值重建.由于通过多次波构建的一次波与真实的一次波存在振幅和相位方面的差异,提出通过基于非平稳自回归过程的自适应预测误差滤波器来表征虚拟一次波的能量谱,利用最小二乘反演方法重建近炮检距缺失数据,自适应预测误差滤波器通过求解正则化约束下的数学欠定问题来实现局部自适应特征.通过对Sigsbee2B模型和实际数据的测试结果表明新方法可以合理地重建复杂的近炮检距缺失数据. 相似文献
14.
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
15.
16.
均衡拟多道匹配滤波法在波动方程法压制多次波中的应用 总被引：7，自引：6，他引：7
本文针对单道最小二乘自适应匹配滤波方法在一次波和多次波分量不正交的情况下不能获得正确匹配的问题，提出均衡拟多道最小二乘自适应匹配滤波方法，该方法采取在空间方向上均衡的办法，使得均衡范围内记录中的一次波和多次波分量总是正交的，并结合拟多道最小二乘自适应匹配能更好匹配记录波形的特点，使得该方法取得很好的自适应匹配效果.通过对简单模型、SEG/EAGE SMAART模型和实际资料压制多次波的处理，结果表明该方法效果良好. 相似文献
17.
多次波压制方法的研究一直都是地震数据处理中非常重要的一个课题.由于常用的多次波匹配方法主要针对多次波模型和实际多次波存在的振幅或相位的差异进行匹配校正,而无法直接校正多次波模型和实际多次波存在时移误差.本文构建了一种复曲波变换的算法,利用复曲波变换的时移不变性质,通过调整复曲波系数的振幅和相位实现对多次波模型振幅和时移误差的校正.为了更好地保护有效信号,在一次波和多次波分离前,引入一个非线性屏蔽滤波器,可以事先分离出大部分有效波,然后再将剩余部分数据作为输入数据,在复曲波域进行剩余一次波和多次波分离.最后通过模型试算和实际资料处理验证了本文提出的一次波和多次波分离方法的有效性. 相似文献
18.
R.-G. FERBER 《Geophysical Prospecting》1987,35(2):129-134
The spectral function of a plane layered medium, which represents the net downgoing energy in the first layer due to a normally incident impulsive plane wave, plays an important role in the solution of the one-dimensional inverse problem in reflection seismology. Hitherto the extension to non-normal incidence was known only for a medium with free surface. By giving the extension for arbitrary surface reflection coefficients, this paper fills a gap. 相似文献
19.
F. AMINZADEH 《Geophysical Prospecting》1984,32(5):819-827
In this paper we develop a recursive algorithm to obtain the layer parameters of an elastic medium (density, P-wave velocity, S-wave velocity) from reflection coefficient matrices in terms of energy flux ratios for a non-normal incidence case. We define a layer impedance matrix, analogous to the impedance of an acoustic medium. Next we derive a matrix relationship between the layer impedance matrix of the n+ 1st layer and the reflection coefficient and parameter matrices of the nth layer. This relationship leads to recursively computing the parameters of the subsurface. We show that the elastic case—unlike the acoustic case—allows one to recover the layer parameters from the impedance matrix for non-normal incidence. The results of this work play a key role in the solution of the inverse problem with non-normal-incidence plane-wave seismic data when using a downward continuation technique. 相似文献
20.
ARNIM B. HAASE 《Geophysical Prospecting》1992,40(4):403-427
Methods for predicting and attenuating water-bottom multiples by wavefield extrapolation have been discussed by several investigators. Because these prediction methods operate on shot records, boundary conditions must be specified for every shot record. The approach presented operates in the common-offset plane; a model of expected water-bottom multiples is generated from the observed surface wavefield using a finite-difference wave-equation migration algorithm with an offset term. An accurate water-depth profile is required, but there is no restriction on the shape of the water bottom other than a dip limit of approximately 18–20°. In generating a multiple model, the water-bottom primary and each water-bottom multiple reflection of the observed surface wavefield are extrapolated to a higher order. Thus, the extrapolated water-bottom primary of the model is lined up with a water-bottom multiple in the data and each multiple in the model is lined up with a higher-order (or later) multiple in the data. Prestack multiple attenuation is achieved, for one offset at a time, by first adapting the model of expected multiples to the observed data and then subtracting the predicted multiple energy. An error-constrained adaptation algorithm is proposed in order to control instabilities. No assumptions are made about primary reflections and no subwater-bottom velocities are required. Computational efficiency of modelling and adaptation can be improved by applying this method only to near and intermediate offsets as the stacking process usually provides sufficient multiple attenuation at far offsets. A field data example demonstrates the potential of the proposed method for improving the primary-to-multiple ratio in prestack and post-stack data. 相似文献