共转换点道集S变换谱相似性的多波地震数据横波波场提取技术

横波速度动校正后的共转换点(CCP)道集内,同时刻的各道横波信号S变换(ST)谱与其叠加道ST谱具有相似关系.因此,可基于这种相似关系设计自适应滤波器来提取多波地震数据中的横波波场.首先对共中心点(CMP)道集应用纵波速度动校正并在各道减去叠加道来去除数据中的纵波波场;然后在CCP道集应用横波速度动校正,将地震道振幅水平调整至叠加道振幅水平并做S变换,以叠加道ST谱为参考对地震道ST谱进行自适应滤波,去除数据中的残余纵波和噪声;最后,将滤波结果的振幅水平恢复至滤波前振幅水平.理论和实际数据试算表明,本文方法可有效提取多波地震数据中的横波波场,为多波多分量横波数据处理提供新思路.     

WEIGHTED STACKING OF SEISMIC DATA USING AMPLITUDE-DECAY RATES AND NOISE AMPLITUDES1

The signal-to-noise (S/N) ratio of seismic reflection data can be significantly enhanced by stacking. However, stacking using the arithmetic mean (straight stacking) does not maximize the S/N ratio of the stack if there are trace-to-trace variations in the S/N ratio. In this case, the S/N ratio of the stack is maximized by weighting each trace by its signal amplitude divided by its noise power, provided the noise is stationary. We estimate these optimum weights using two criteria: the amplitude-decay rate and the measured noise amplitude for each trace. The amplitude-decay rates are measured relative to the median amplitude-decay rate as a function of midpoint and offset. The noise amplitudes are measured using the data before the first seismic arrivals or at late record times. The optimum stacking weights are estimated from these two quantities using an empirical equation. Tests with synthetic data show that, even after noisy-trace editing, the S/N ratio of the weighted stack can be more than 10 dB greater than the S/N ratio of the straight stack, but only a few decibels more than the S/N ratio of the trace equalized stack. When the S/N ratio is close to 0 dB, a difference of 4 dB is clearly visible to the eye, but a difference of 1 dB or less is not visible. In many cases the S/N ratio of the trace-equalized stack is only a few decibels less than that of the optimum stack, so there is little to be gained from weighted stacking. However, when noisy-trace editing is omitted, the S/N ratio of the weighted stack can be more than 10 dB greater than that of the trace-equalized stack. Tests using field data show that the results from straight stacking, trace-equalized stacking, and weighted stacking are often indistinguishable, but weighted stacking can yield slight improvements on isolated portions of the data.     

Reliability Evaluation on Weak Signal Extraction for Airgun Source Surveys

Based on the data synthesis simulation and the actual processing of the airgun seismic source signal, three quantitative indicators of signal-to-noise ratio, waveform correlation coefficient and phase offset, are superimposed. We systematically evaluate the functions of the following three stack methods including linearity, phase weighting and S-transform in the extraction of weak signals under strong background noise and quantitatively estimate the reliability of the stack results. Through the comprehensive discussion of the above three methods of stack results, the preliminary comparative analysis believes that the linear stack signal-to-noise ratio is low, but the waveform distortion is minimal; the phase-weighted superimposed signal-to-noise ratio is high and the phase offset is small, but the results of the waveform quality and linear stack are larger than the deviation; the S-transform stack has a relatively higher signal-to-noise ratio and a small loss of waveform amplitude, but there is a certain phase shift phenomenon. It is therefore suggested that linear stack technology should be used when the requirements of both waveform quality and time precision are high. However, the selection of the stack method when the airgun source excitation is limited should be emphasized. If high fidelity is required, the S-transform stack method should be selected; if the required time is high, accuracy can be selected by phase-weighted stack method to achieve reasonable extraction of weak signals.     

二维菲涅耳带共反射面元叠加方法研究

大量研究证明CRS叠加能提高地震勘探的信噪比,但是能否提高分辨率的关键在于如何确定CRS叠加孔径.本文详细探讨了地震波反射过程中菲涅耳带的特征,认为起伏地形下菲涅耳带可以采用椭圆予以近似,在此基础上提出了一种通过菲涅耳带来确定CRS叠加孔径的方法,并应用于泌阳凹陷陡坡带的地震剖面.结果表明,由于菲涅耳带确定的叠加范围使地震信号的能量达到最佳,相对于CMP叠加,菲涅耳带CRS叠加同时提高了地震资料的信噪比和分辨率,特别显示了中深部较弱的地震信息,而常规的CRS叠加则只在于提高资料的信噪比和改善浅部的地震信息.     

AUTOMATIC EDITING OF NOISY SEISMIC DATA1

Seismic data often contain traces that are dominated by noise; these traces should be removed (edited) before multichannel filtering or stacking. Noise bursts and spikes should be edited before single channel filtering. Spikes can be edited using a running median filter with a threshold; noise bursts can be edited by comparing the amplitudes of each trace to those of traces that are nearby in offset-common midpoint space. Relative amplitude decay rates of traces are diagnostic of their signal-to-noise (S/N) ratios and can be used to define trace editing criteria. The relative amplitude decay rate is calculated by comparing the time-gated trace amplitudes to a control function that is the median trace amplitude as a function of time, offset, and common midpoint. The editing threshold is set using a data-adaptive procedure that analyses a histogram of the amplitude decay rates. A performance evaluation shows that the algorithm makes slightly fewer incorrect trace editing decisions than human editors. The procedure for threshold setting achieves a good balance between preserving the fold of the data and removing the noisiest traces. Tests using a synthetic seismic line show that the relative amplitude decay rates are diagnostic of the traces’S/N ratios. However, the S/N ratios cannot be accurately usefully estimated at the start of processing, where noisy-trace editing is most needed; this is the fundamental limit to the accuracy of noisy trace editing. When trace equalization is omitted from the processing flow (as in amplitude-versus-offset analysis), precise noisy-trace editing is critical. The S/N ratio of the stack is more sensitive to type 2 errors (failing to reject noisy traces) than it is to type 1 errors (rejecting good traces). However, as the fold of the data decreases, the S/N ratio of the stack becomes increasingly sensitive to type 1 errors.     

3D3C陆地反射PS转换波CMP成像影响因素分析

三维三分量(3D3C)陆地反射PS转换波共中心点(CMP)叠加成像方法,虽然抽道集简单,但是对实际资料处理结果往往不理想.尤其当反射界面为三维倾斜界面时,其成像质量较差.本文提出有三个主要因素影响其成像质量:第一,转换点离散.运用实例计算得出,转换点离散度随着纵横波速度比、偏移距和界面倾角的增大而增大.相同界面倾角,不同测线方位的转换点离散度不同,视倾角的绝对值越大离散度也越大;第二,道集内静校正量差异增大.CMP道集中,由于转换点离散使得转换点横向跨度较大,经倾斜界面反射转换的S波出射到近地表地层时的角度差异也较大,导致静校突出;第三,加大动校叠加复杂性.三维倾斜界面PS波CMP道集近炮检距时距方程可表示为双曲形式,但是曲线的顶点位置和动校速度同时随测线方位变化,使得CMP道集同相轴很难校平,动校叠加过程很复杂.     

复杂地表条件下共反射面元(CRS)叠加方法研究

在地表地形复杂的情况下,静校正不易做好,这是制约山地资料处理质量的一个很重要的因素.复杂地表共反射面元（CRS）叠加不需对叠前数据做静校正,而且在得到叠加剖面后可以利用叠加得到的波场参数剖面实现基准面重建.地震数据的试算表明,复杂地表CRS叠加得出的剖面与常规处理剖面相比有着较高的信噪比和同相轴连续性.与水平地表CRS叠加不同的是,在复杂地表CRS叠加的时距公式中,波场三参数耦合,难以通过简化CRS道集的方法将它们全部分离并逐个优化.引入模拟退火算法后,有效地解决了这一组合优化的难题.     

Common-reflection-surface stack — a real data example

The simulation of a zero-offset (ZO) stack section from multi-coverage reflection data is a standard imaging method in seismic processing. It significantly reduces the amount of data and increases the signal-to-noise ratio due to constructive interference of correlated events. Conventional imaging methods, e.g., normal moveout (NMO)/dip moveout (DMO)/stack or pre-stack migration, require a sufficiently accurate macro-velocity model to yield appropriate results, whereas the recently introduced common-reflection-surface stack does not depend on a macro-velocity model. For two-dimensional seismic acquisition, its stacking operator depends on three wavefield attributes and approximates the kinematic multi-coverage reflection response of curved interfaces in laterally inhomogeneous media. The common-reflection-surface stack moveout formula defines a stacking surface for each particular sample in the ZO section to be simulated. The stacking surfaces that fit best to actual events in the multi-coverage data set are determined by means of coherency analysis. In this way, we obtain a coherency section and a section of each of the three wavefield attributes defining the stacking operator. These wavefield attributes characterize the curved interfaces and, thus, can be used for a subsequent inversion. In this paper, we focus on an application to a real land data set acquired over a salt dome. We propose three separate one-parametric search and coherency analyses to determine initial common-reflection-surface stack parameters. Optionally, a subsequent optimization algorithm can be performed to refine these initial parameters. The simulated ZO section obtained by the common-reflection-surface stack is compared to the result of a conventional NMO/DMO/stack processing sequence. We observe an increased signal-to-noise ratio and an improved continuity along the events for our proposed method — without loss of lateral resolution.     

共反射元弧叠加方法在火山岩成像中的应用

常规叠加方法假设叠加的地震道集的反射波来自地下同一个反射点,而地表观测到 的反射波场在空间上小于菲涅尔体范围是不可分辨的. 本文根据火山岩体特征,用元弧描述 火山岩的反射界面. 将来自菲涅尔体范围内的反射波沿着元弧界面求和,进而扩大叠加次数 ,达到增加反射信号能量提高地震反射波的叠加成像质量的目的. 文中给出了反射波走时参 数与地下元弧反射界面之间的联系和叠加实现的步骤. 计算结果表明,元弧叠加方法能够提 高剖面的信噪比,增加反射波同相轴的连续性.     

地震数据处理中的相位校正技术综述

提高地震剖面的信噪比和分辨率始终是地震数据处理中研究的重要内容.在动静校正后的同一道集内振幅和相位相同的假设条件下,地震叠加技术能明显提高资料的信噪比.实际资料中相位差问题是影响有效反射信号实现同相叠加的重要因素之一.相位校正技术能够消除子波的相位谱差异,使子波接近或达到零相位,从而达到提高叠加剖面质量的目的.对相位校正的国内外研究现状,影响相位变化的因素,相位校正的方法原理以及判别准则进行了系统的总结和概述.通过分析总结得出:随着勘探形势的发展,地震资料中的相位问题将越来越受到人们的关注和重视,对相位的研究也将成为今后的攻关课题和研究热点.     

低信噪比转换波地震资料静校正(英文)

Converted waves have slow velocity and low signal-to-noise ratio. It is also difficult to pick first-breaks and bin the common-conversion-points （CCP）. Some statics methods, which work well for P-wave data, can＇t be effectively used for solving convertedwave statics problems. This has become the main obstacle to breakthroughs in convertedwave data processing. To improve converted-wave static corrections, first, a statics method based on the common-receiver-point （CRP） stack is used for the initial receiver static correction to enhance the coherency of the CRP stack. Second, a stack-power-maximization static correction which improves the continuity of the CCP stack is used for detailed receiver statics. Finally, a non-surface-consistent residual moveout correction of the CCP gathers is used to enhance the stack power of reflection signals from different depths. Converted-wave statics are solved by the joint use of the three correction methods.     

共接收点倾斜叠加波动方程偏移

共接收点倾斜叠加波动方程偏移,本质上是一种叠前偏移方法.每给定一个斜率P,对经过叠前（动校正前）常规处理的地震记录中的各共接收点道集,沿直线t=τ+px进行倾斜叠加,就形成一个共接收点倾斜叠加剖面.对之进行波动方程偏移,该偏移剖面将代表地下真实构造.对一系列的p,我们可以得到一系列这样的偏移剖面.对它们作共接收点叠加,偏移叠加剖面的信噪比将超过水平叠加剖面.本文导出了在均匀、水平层状及非均匀介质条件下的共接收点倾斜叠加波动方程偏移算法.     

不依赖源子波的跨孔雷达时间域波形反演

波形反演是近年来较热门的反演方法,其分辨率可以达到亚波长级别.在波形反演的实际应用中,源子波的估计十分重要.传统方法使用反褶积来估计源子波并随着反演过程更新,该方法在合成数据波形反演中效果较好,但在实际数据反演过程中存在一系列的问题.由于实际数据信噪比较低,在源子波估计过程中需要大量的人为干涉,且结果并不一定可靠.本文使用一种基于褶积波场的新型目标函数,令反演过程不再依赖源子波.详细推导了针对跨孔雷达波形反演的梯度及步长公式,实现介电常数和电导率的同步反演.针对一个合成数据模型同时反演介电常数和电导率,结果表明该方法能够反演出亚波长尺寸异常体的形状和位置.接着,将该方法应用到两组实际数据中,并与基于估计源子波的时间域波形反演结果进行比较.结果表明不依赖源子波的时间域波形反演结果分辨率更高,也更准确.     

STUDY AND APPLICATIONS OF SPATIAL DIRECTIONAL FILTERING IN THREE-COMPONENT RECORDINGS1

Three-component recordings permit the construction of particle trajectories. These three-dimensional pictures of particle motion show successive predominant directions of polarization and allow wave modes with distinct polarization directions to be recognized. A polarization selection, called ‘spatial directional filtering’, can be accomplished by several methods; four techniques are described. The application of these polarization filters to a noise shot, offset VSPs and CDP stack are also presented. This type of filtering is shown to cancel waves with undue polarization and to enhance the signal-to-noise ratio.     

对共反射面叠加的进一步探讨

共反射面元（CRS）叠加考虑了反射层的局部特征和第一菲涅耳带内的全部反射,更充分挖掘了多次覆盖数据的潜力.但在地下介质复杂并存在倾斜层时存在反射点分散的情况,从而影响了CRS叠加效果.本文从射线理论出发,在考虑反射层局部特征的情况下,推导了水平地表和起伏地表情况下计算真实反射点分散程度的公式,最终将反射点分散程度定量表达出来.通过对反射点分散程度的控制,从CRS道集中抽取出共反射点（CRP）道集,在CRP道集中而不是在CRS道集中实现叠加,其效果应比传统的CRS叠加效果要好.利用水平地表和起伏地表的模型验证了本文所推导的公式的正确性和有效性.该公式在实际资料处理中的运用尚待进一步研究.     

Treatment of conflicting dips in the 3D common-reflection-surface stack

The 3D common-reflection-surface stack is a tool to simulate zero-offset sections from the prestack data. In conventional implementations conflicting dip situations, i.e., the contribution of more than one stacking operator per output location, are not taken into account. This leads to stacked sections with fragmentary events and to incomplete sets of stacking parameters. Subsequent applications based on the results of the common-reflection-surface stack and its attributes will show deteriorated quality.
In this paper, I present a modified workflow for the handling of the conflicting dip problem in context of the 3D common-reflection-surface stack. The strategy utilizes the path-summation technique to obtain an improved input for the conflicting dip search in the zero-offset domain. The actual detection is done by means of an adapted peak detection algorithm. For each detected event consistent sets of attributes are obtained by a newly introduced search step.
Two 3D real data applications show the applicability of the proposed technique. The strategy proves to resolve most of the conflicting dip situations even for poor signal-to-noise ratio. With only moderate additional computational cost the presented method provides superior results compared to the conventional 3D common-reflection-surface stack.     

Common-Reflection-Surface Stack for Converted Waves

The finite-offset (FO) common-reflection-surface (CRS) stack has been shown to be able to handle not only P-P or S-S but also arbitrarily converted reflections. It can provide different stack sections such as common-offset (CO), common-midpoint (CMP) and common-shot (CS) sections with significantly increased signal-to-noise ratio from the multi-coverage pre-stack seismic data in a data-driven way. It is our purpose in this paper to demonstrate the performance of the FO CRS stack on data involving converted waves in inhomogeneous layered media. In order to do this we apply the FO CRS stack for common-offset to a synthetic seismic data set involving P-P as well as P-S converted primary reflections. We show that the FO CRS stack yields convincing improvement of the image quality in the presence of noisy data and successfully extracts kinematic wavefield attributes useful for further analyses. The extracted emergence angle information is used to achieve a complete separation of the wavefield into its P-P and P-S wave components, given the FO CRS stacked horizontal and vertical component sections.     

Automatic stacking‐velocity estimation using similarity‐weighted clustering

Local seismic event slopes contain subsurface velocity information and can be used to estimate seismic stacking velocity. In this paper, we propose a novel approach to estimate the stacking velocity automatically from seismic reflection data using similarity‐weighted k‐means clustering, in which the weights are local similarity between each trace in common midpoint gather and a reference trace. Local similarity reflects the local signal‐to‐noise ratio in common midpoint gather. We select the data points with high signal‐to‐noise ratio to be used in the velocity estimation with large weights in mapped traveltime and velocity domain by similarity‐weighted k‐means clustering with thresholding. By using weighted k‐means clustering, we make clustering centroids closer to those data points with large weights, which are more reliable and have higher signal‐to‐noise ratio. The interpolation is used to obtain the whole velocity volume after we have got velocity points calculated by weighted k‐means clustering. Using the proposed method, one obtains a more accurate estimate of the stacking velocity because the similarity‐based weighting in clustering takes into account the signal‐to‐noise ratio and reliability of different data points in mapped traveltime and velocity domain. In order to demonstrate that, we apply the proposed method to synthetic and field data examples, and the resulting images are of higher quality when compared with the ones obtained using existing methods.     

频谱代换无拉伸动校正方法研究

动校正拉伸是地震资料处理的一个基本问题,解决拉伸问题的处理方法是切除.现代地震数据大多为长排列采集,动校正拉伸更为严重.依据褶积模型和Fourier变换的基本性质,本文给出频谱代换无拉伸动校正方法.算法实现就是将CMP道集变换到频率域,取参考道的相位谱替换其它偏移距道的相位,同时保持其振幅谱不变,再做Fourier反变换就得到动校正后的地震剖面.通过其实现过程可知该方法不需要地下介质的速度信息,算法可完全自动实现,且具有较高的计算效率.频谱代换无拉伸动校正可适用于任何偏移距的地震资料,而且还可有效保持地震资料的AVO效应.理论模拟数据及其叠加结果显示频谱代换法的有效性和实用性,同时该方法具有较强的抗随机噪音能力.     

台阵地震学方法及对间断面结构的研究进展

地震台阵是为了监测核爆而发展起来的一种地震观测系统。近年来,地震台阵被推广到地球内部速度间断面的研究中并极大地推动了地震学的发展。本文主要介绍处理台阵资料的技术方法,如聚束、倾斜叠加、N次根叠加、频率波数法以及相位加权叠加等,并讨论各种方法的优缺点。在提取微弱但相关信号方面,重点讨论相位加权叠加方法及现有的研究成果。结果表明,这些方法都在不同程度上提高了记录的信噪比,高质量的台阵数据使得地球内部速度结构的成像研究更加精细。