共偏移距道集平面波叠前时间偏移与反偏移

在Dubrulle提出的共偏移距道集频率波数域叠前时间偏移的基础上,提出了共偏移距道集频率波数域叠前时间偏移与反偏移一对共轭算子.讨论了该对算子的变孔径实现过程.并把该对共轭算子串连起来实现了叠前地震数据的规则化处理.指出最小二乘意义下的叠前地震数据规则化会得到更好的效果.v(z)介质模型和Marmousi模型的数值试验结果表明,方法理论正确、有效.     

粘弹性介质单程波法非零偏移距地震数值模拟与偏移

地震资料分辨率降低,得不到深层介质的精确信息实际上是由于大地吸收效应的影响.同时与双程波动方程相比单程波动方程避免了多次波的干扰并且计算效率高、占用内存少.本文首先基于开尔芬粘弹性介质模型将品质因子与单程波分步傅立叶法波场延拓算子相结合,实现了粘弹性介质波场延拓,从而将单程波弹性介质波场延拓推广到了粘弹性介质.然后在定位原理,数学检波器原理以及等时叠加原理的基础之上实现了粘弹性介质非零偏移距叠前正演模拟.最后将数值模拟得到的正演记录进行弹性偏移和粘弹性偏移并进行对比分析.通过数值算例可以看出,粘弹性介质叠前正演深层的反射波能量减弱,同相轴变粗,频带变窄,主频减小,分辨率降低;粘弹性偏移不但实现了振幅的恢复,而且同时偏移剖面的垂向空间分辨率也得到了提高.     

长偏移距地震资料的优化契比雪夫动校正方法

传统的双曲型动校正方法仅适用于偏移距与目标层深度比值较小的情况.对于长偏移距地震资料,须采用非双曲动校正公式才能得到较高的动校正精度.但常规的非双曲方法对于大偏移距仍然有较大的误差.本文提出契比雪夫截断加模拟退火优化的思路:通过沿用高阶项补偿系数的形式以克服对于大偏移距可能存在的不稳定现象,然后对常规的泰勒展开进行契比...     

VTI介质长偏移距非双曲动校正公式优化

常规Alkhalifah动校正公式精度低,不能精确描述各向异性介质长偏移距地震反射同相轴的时距关系.本文以提高VTI介质长偏移距地震资料动校正公式的精度为目标,在分析VTI介质常规动校正方程的基础上,根据误差最小原理建立优化校正系数图版,实现对常规动校正公式大偏移距误差的修正,建立最优化校正Alkhalifah动校正方程,实现了对VTI介质长偏移距地震资料常规动校正方程的改进.之后由Fomel群速度公式导出高精度VTI模型长偏移距时距函数,提出了高精度VTI介质长偏移距地震资料动校正方程.将以上的动校正方程用于各向异性参数反演,模型计算表明最优化校正Alkhalifah动校正方程的反演精度是常规长偏移距动校正方程反演精度的2～4倍,高精度动校正方程的反演精度是常规动校正方程反演精度的2～8倍.     

共炮检距高斯波束偏移的一种快速实现算法

与共炮高斯波束偏移相比,共炮检距高斯波束偏移具有直接抽取炮检距域共成像点道集的优势.过去,共炮检距高斯波束偏移以损失成像精度的代价采用最速下降法来降低积分的维数,从而提高计算效率.但经过最速下降近似简化的偏移公式仍是频率域的,需要在每个频点进行计算.为此,本文提出一种快速实现算法来避免采用最速下降法.本文通过分析一个水平层状速度模型的偏移过程和Marmousi速度模型的成像结果来检验不同插值方法对快速实现算法的成像精度和计算效率的影响,并建议采用二维三次卷积插值方法.同时本文在Marmousi速度模型下验证了快速实现算法相对于最速下降法在成像精度和计算效率上的优势.此外,本文将采用二维三次卷积插值的快速实现算法应用于Sigsbee2A模型并获得了清晰的盐下图像.     

Kirchhoff型偏移反偏移串联地震数据炮检距转换技术

零炮检距数据在海洋地震资料处理中有很多优势和用途,然而,受海洋水平拖缆地震采集作业方式的限制,接收数据的最小炮检距一般在200 m左右,小于该炮检距的数据是无法直接获得的.通常的做法是通过对较大炮检距数据进行动校,通过外推来变相获得零炮检距（包括小炮检距）数据,其外推的精度会受到地震资料信噪比、动校正速度的精度等因素影响,并且保幅性较差.本文通过一种基于Kirchhoff真振幅偏移和反偏移串联的技术,在反偏移过程中改变观测系统,有效实现了大炮检距反射地震数据向零炮检距（包括小炮检距）数据之间的转换,且很好地保持了零炮检距（包括小炮检距）数据的振幅特性.同时,经偏移-反偏移串联处理后,有效压制了地震数据中的随机噪声,地震资料信噪比和成像精度均得到显著提高.

     

地震波场的共偏移距延拓研究

实现地震波场共偏移距剖面上不同偏移距之间的转换,对于精确的共反射点叠加、速度分析以及研究ＡＶＯ信息等皆具有重要意义。本文从非均匀介质地震记录的微分性质出发,通过对其共反射点变化轨迹的研究,导出基于Ｈａｍｉｌｔｏｎ方程的地震波场共偏移距延拓方程,建立了新的共偏移距延拓算子,通过理论模型的计算验证了此方程的正确性。     

抛物Radon变换法近偏移距波场外推

本文给出了抛物Radon变换的基本原理,以及部分动校正后的CMP道集抛物线近似有效性的证明,基于带限正反最小平方抛物Radon变换的Levinson递推算法,对缺失的近偏移距地震波场进行叠前重建和外推.给出了抛物Radon变换法地震道重建外推的基本原理和叠前地震数据规则化的处理流程,另外对于Radon域均匀采样的情形,本文给出了均匀层状介质和Marmousi模型的近偏移距外推结果,计算结果验证了算法的稳定性和适用性.     

三维偏移距平面波有限差分叠前时间偏移

本文提出了中点-半偏移距域内的三维偏移距平面波(offset plane-wave)方程,并给出了其有限差分解法.偏移距平面波可通过对CMP道集进行平面波分解(倾斜叠加或线性Radon变换)生成,然而这样做会产生严重的噪音干扰.本文提出了局部倾斜叠加方法(local slant-stacking)来消除离散线性Radon变换引入的噪音.针对实际三维数据的不规则性(中点-偏移距域内方位角展布不均匀及偏移距采样不规则),本文还提出了与方位角无关的三维倾斜叠加方法(azimuth-independent 3D slant-stacking),解决了三维平面波分解中存在的问题.使用文中提出的平面波分解方法,可以得到高信噪比的偏移距平面波数据体.同时,三维偏移距平面波偏移可以输出偏移距射线参数域共成像点道集,基于此道集的剩余速度分析方法可以用来更新偏移速度场.偏移距平面波偏移具有很高的计算效率,相较Kirchhoff积分叠前时间偏移有较好的保幅特性,可作为水平地表三维叠前时间偏移的一个很好的解决方案.     

地震波场的共偏移距延拓研究

实现地震波场共偏移距剖面上不同偏移距之间的转换,对于精确的共反射点叠加、速度分析以及研究ＡＶＯ信息等皆具有重要意义。本文从非均匀介质地震记录的微分性质出发,通过对其共反射点变化轨迹的研究,导出基于Ｈａｍｉｌｔｏｎ方程的地震波场共偏移距延拓方程,建立了新的共偏移距延拓算子,通过理论模型的计算验证了此方程的正确性。     

An approximation to the P-wave reflection coefficient for amplitude variation with long-offset seismic data

近年来,长偏移距排列逐渐被大量应用到海上勘探。传统AVO分析都是小入射角,对于长偏移距数据来说有很大不足。为了探讨拓宽AVO分析的研究范围,本文推导了长偏移距时P波反射系数的一种近似公式,并讨论了其精确性。本文的结果和广泛应用的Shuey公式相类似,Shuey公式可以看作本文结果在小入射角情况的简化。     

任意空间取向TI介质中长排列非双曲动校正公式优化(英文)

常规长排列非双曲动校正公式是在VTI介质中得到的,它不能满足任意空间取向TI(ATI)条件下的扩展.本文以VTI介质中非双曲动校正公式为基础,基于我们推导得出的ATI介质中精确四次时差系数解析解和NMO速度解析解,给出ATI介质中长排列优化的非双曲动校正公式.通过与各向异性射线追踪方法计算所得出的"精确走时"结果对比,研究表明优化后的非双曲动校正公式能精确地描述任意强弱、ATI介质中随测线方位变化的走时曲线,可以用来替代耗时、多偏移距、多方位的射线追踪方法正演拟合ATI介质中长偏移距反射走时,为利用非双曲时距的各向异性参数反演提供理论基础性认识。     

Lithology-dependent seismic anisotropic amplitude variation with offset correction in transversely isotropic media

Analysis of amplitude variation with offset is an essential step for reservoir characterization. For an accurate reservoir characterization, the amplitude obtained with an isotropic assumption of the reservoir must be corrected for the anisotropic effects. The objective is seismic anisotropic amplitude correction in an effective medium, and, to this end, values and signs of anisotropic parameter differences (Δδ and Δε) across the reflection interfaces are needed. These parameters can be identified by seismic and well log data. A new technique for anisotropic amplitude correction was developed to modify amplitude changes in seismic data in transversely isotropic media with a vertical axis of symmetry. The results show that characteristics of pre-stack seismic data, that is, amplitude variation with offset gradient, can be potentially related to the sign of anisotropic parameter differences (Δδ and Δε) between two layers of the reflection boundary. The proposed methodology is designed to attain a proper fit between modelled and observed amplitude variation with offset responses, after anisotropic correction, for all possible lithofacies at the reservoir boundary. We first estimate anisotropic parameters, that is, δ and ε, away from the wells through Backus averaging of elastic properties resulted from the first pass of isotropic pre-stack seismic inversion, on input data with no amplitude correction. Next, we estimate the anisotropic parameter differences at reflection interfaces (values and signs of Δδ and Δε). We then generate seismic angle gather data after anisotropic amplitude correction using Rüger's equation for the P-P reflection coefficient. The second pass of isotropic pre-stack seismic inversion is then performed on the amplitude-corrected data, and elastic properties are estimated. Final outcome demonstrates how introduced methodology helps to reduce the uncertainty of elastic property prediction. Pre-stack seismic inversion on amplitude-corrected seismic data results in more accurate elastic property prediction than what can be obtained from non-corrected data. Moreover, a new anisotropy attribute (ν) is presented for improvement of lithology identification.     

转换波AVO反演速度比各横波反射系数

Based on the empirical Gardner equation describing the relationship between density and compressional wave velocity, the converted wave reflection coefficient extrema attributes for AVO analysis are proposed and the relations between the extrema position and amplitude, average velocity ratio across the interface, and shear wave reflection coefficient are derived. The extrema position is a monotonically decreasing function of average velocity ratio, and the extrema amplitude is a function of average velocity ratio and shear wave reflection coefficient. For theoretical models, the average velocity ratio and shear wave reflection coefficient are inverted from the extrema position and amplitude obtained from fitting a power function to converted wave AVO curves. Shear wave reflection coefficient sections have clearer physical meaning than conventional converted wave stacked sections and establish the theoretical foundation for geological structural interpretation and event correlation. ＂The method of inverting average velocity ratio and shear wave reflection coefficient from the extrema position and amplitude obtained from fitting a power function is applied to real CCP gathers. The inverted average velocity ratios are consistent with those computed from compressional and shear wave well logs.     

地震波反射系数偏导矩阵的精确解及对近似计算的精度分析

目前叠前反演方法大多是基于Zoeppritz方程近似式实现的,它仅适应于弱反射介质界面、中小角度(或小偏移距)的地震数据反演,不能满足勘探开发的地质需求.本文建立了基于zoeppritz方程精确求解反射系数的梯度矩阵,分析了矩阵特点和精度,为研究利用反射系数梯度精确解反演地震参数奠定了基础.     

An insightful parametrization for the flatlander's interpretation of time‐lapsed seismic data

An approximation is developed that allows mapped 4D seismic amplitudes and time‐shifts to be related directly to the weighted linear sum of pore pressure and saturation changes. The weights in this relation are identified as key groups of parameters from a petroelastic model and include the reservoir porosity. This dependence on groups of parameters explains the inherent non‐uniqueness of this problem experienced by previous researchers. The proposed relation is of use in 4D seismic data feasibility studies and inversion and interpretation of the 4D seismic response in terms of pore pressure and water saturation changes. A further result is drawn from analysis of data from the North Sea and West Africa, which reveals that the relative interplay between the effects of pore pressure and saturation changes on the seismic data can be simplified to the control of a single, spatially variant parameter C_S/C_P. Combining these results with those from published literature, we find that C_S/C_P = 8 appears to be a generality across a range of clastic reservoirs with a similar mean porosity. Using this C_S/C_P value, an in situ seismic‐scale constraint for the rock stress sensitivity component of the petroelastic model is constructed considering this component carries the largest uncertainty.     

Prestack amplitude versus angle inversion for Young's modulus and Poisson's ratio based on the exact Zoeppritz equations

Elastic parameters such as Young's modulus, Poisson's ratio, and density are very important characteristic parameters that are required to properly characterise shale gas reservoir rock brittleness, evaluate gas characteristics of reservoirs, and directly interpret lithology and oil‐bearing properties. Therefore, it is significant to obtain accurate information of these elastic parameters. Conventionally, they are indirectly calculated by the rock physics method or estimated by approximate formula inversion. The cumulative errors caused by the indirect calculation and low calculation accuracy of the approximate Zoeppritz equations make accurate estimation of Young's modulus, Poisson's ratio, and density difficult in the conventional method. In this paper, based on the assumption of isotropy, we perform several substitutions to convert the Zoeppritz equations from the classical form to a new form containing the chosen elastic constants of Young's modulus, Poisson's ratio, and density. The inversion objective function is then constructed by utilising Bayesian theory. Meanwhile, the Cauchy distribution is introduced as a priori information. We then combine the idea of generalised linear inversion with an iterative reweighed least squares algorithm in order to solve the problem. Finally, we obtain the iterative updating formula of the three elastic parameters and achieve the direct inversion of these elastic parameters based on the exact Zoeppritz equations. Both synthetic and field data examples show that the new method is not only able to obtain the two elastic parameters of Young's modulus and Poisson's ratio stably and reasonably from prestack seismic data but also able to provide an accurate estimation of density information, which demonstrates the feasibility and effectiveness of the proposed method. The proposed method offers an efficient seismic method to identify a “sweet spot” within a shale gas reservoir.     

可展宽地震资料有效频宽的随机噪声衰减方法

很多地区地震资料的信噪比较低,而用于压制与信号具有不同方向的随机噪声的常规二维滤波方法常常产生假信息。基于相邻信号具有相干性这一假设,本文提出了一种叠后衰减随机噪声的多道滤波方法。该方法利用信噪比最高的中频段信息(含有主频的这一频率区间)分时窗计算信号单位矢量,并将该时窗内全频段数据向信号单位矢量方向投影,对各时窗(包括时间方向和空间方向)重叠部分按比例进行加权。我们利用这种方法对含有陡倾角的合成地震数据和海上二维实际地震资料进行了处理,处理效果很好。这种方法较为费时,但不受倾角限制,应用范围广。     

Suppressing random noise to broaden the useful bandwidth of seismic reflection data

The signal-to-noise ratio （SNR） of seismic reflection data in many areas is rather poor and conventional two-dimensional filters designed to suppress noise with different moveout from the signal tend to generate artifacts. We have extended a method of multichannel filtering, based on the hypothesis that signals on adjacent channels are similar, for enhancing the SNR on stacked sections. Using only the mid-range frequencies where the SNR is highest, the event trend is found for overlapping windows on the section and the average signal vector is calculated. Then the data from the full bandwidth section are projected onto the spatially varying unit similarity vectors and the results are merged for the overlapping windows. Application of the method to synthetic data containing steeply dipping events and to a stacked section for a marine 2D line has produced good results. The modifications we have introduced carry a small overhead in computing time but they should enable the method to be used effectively even on sections containing steep dips.     

Receiver function analysis for seismic structure of the crust and uppermost mantle in the Liupanshan area, China

A portable broadband seismic array was deployed from the northeast Tibetan Plateau to the southwest Ordos block, China. The seismic structure of the crust and uppermost mantle of the Liupanshan area is obtained using receiver function analysis of teleseismic body waves. The crustal thickness and Poisson's ratios are estimated by stacking the weighted amplitudes of receiver functions. Our results reveal complex seismic phases in the Liupanshan area, implying intense deformation at the boundary between the Tibetan Plateau and the Ordos block. The average crustal thickness is 51.5 km in the northeast Tibetan Plateau, 53.5 km in the Liupan Mountain and 50 km in the southwest Ordos block, resulting in a concave Moho beneath the Liupan Mountain. The Poisson's ratio of the Liupanshan area varies between 0.27-0.29, higher than the value of 0.25-0.26 to the east and west of the Liupan Mountain, suggesting partial melting in the lower crust. The variance in Poisson's ratio across the Liupan Mountain indicates notable changes in the crustal composition and mechanical properties, which may be formed by the northeastward flow of the Tibetan lower crust during the India-Eurasia collision.