Numerical modeling of PP- and PS-wave azimuthal anisotropy in HTI media

This study focuses on the factors that may affect the feasibility of performing elliptical anisotropy analysis on azimuthal PP- and PS-wave data in HTI media, with the aim of using the modeling results as guidance in real seismic data application. Our results reveal that there is an offset limitation for both PP- and PS-waves in elliptical anisotropy fitting, and that PS-waves show a wider applicable offset range and larger observable azimuthal anisotropy than PP-waves. The major axis of the elliptical fit to the amplitudes of the R-component is perpendicular to the fracture strike, which is opposite to that in PP-wave analysis. The azimuthal interval travel time of PS-waves shows a nearly elliptical distribution and the major axis of the fit ellipse is perpendicular to the fracture strike, which is same as that in PP-wave analysis. For data within the applicable offset range, the anisotropic magnitude obtained from amplitude and travel time attributes of PP- and PS-waves exhibits a dependence on fracture density, and the major to minor axis ratio of the fit ellipse may be used to infer the relative distribution of fracture densities.     

东濮凹陷的各向异性叠前深度偏移方法

东濮凹陷属断陷型盆地,沉积环境多变、断块破碎、构造复杂,局部构造主要受断层控制,断层两侧同一时代地层由于埋深不同,导致在大断层附近存在较大的速度横向变化.而时间偏移不能解决速度横向变化的问题,东濮凹陷今后构造勘探的主要目标是小断块和小幅度构造,所以在本区中应用了各向异性叠前深度偏移,在叠前深度偏移基础上,把时间偏移道集的高密度速度分析结果与声波测井资料相结合,形成一套各向异性参数求取方法,通过基于各向异性的叠前深度偏移改善了地震与钻井的吻合度.     

层状各向异性介质转换波克希霍夫叠前时间偏移

在克希霍夫叠前时间偏移处理中,地震波走时的计算方法是决定大偏移距地震资料成像品质的重要因素.在常规的三维转换波各向异性叠前时间偏移公式中,走时的计算是基于等效单层各向异性介质的非双曲线方法.用这种方法处理的成像道集,在偏移/深度比超过一定阈值后,成像道集中的反射同相轴将出现过偏现象,这种偏移不平的同相轴将影响偏移叠加的最佳响应,使得偏移成像波组呈低频化特征,最终降低三维转换波偏移成像质量.我们采用层状介质的走时计算方法代替常规算法,并且利用了常规方法的转换波各向异性偏移速度模型.基于层状介质的算法能够提高大偏移距转换波走时计算精度,克服中浅地层大偏移距远道成像道集中反射同相轴逐渐上翘的问题.两个地区的三维转换波资料处理结果证实,基于层状各向异性介质的转换波克希霍夫叠前时间偏移方法,明显改善了反射成像剖面的连续性和分辨率,提高成像剖面构造的可解释性.     

各向异性介质Low-rank有限差分法纯qP波叠前平面波最小二乘逆时偏移

拟声波最小二乘逆时偏移是一种极具潜力的地震波成像工具,但该方法遭受各向异性拟声波近似的限制,TTI介质正演模拟不稳定、反偏移记录中遭受伪横波二次扰动及数值频散假象,另外拟声波最小二乘逆时偏移还面临计算效率低、收敛速度慢、对速度等模型参数依赖性高等问题.为了克服各向异性拟声波最小二乘逆时偏移的缺陷,在反演框架下,本文借助Low-rank有限差分算法首次提出并实现了TTI介质纯qP波线性正演模拟及纯qP波最小二乘逆时偏移;为了进一步提升反演成像效率,同时改善反演成像方法对模型参数误差的依赖性及对地震数据噪声的适应性,通过引入叠前平面波优化策略,发展了TTI介质纯qP波叠前平面波最小二乘逆时偏移成像方法.在编程实现方法的基础上,通过开展模型成像测试,展示了本方法的优势和潜力：一方面加快了反演成像效率,另一方面也提升了方法的抗噪性,同时还降低了方法对模型参数的依赖性.

     

各向异性叠前时间偏移——以东濮凹陷为例

建立精准的偏移速度场是复杂地质构造成像的核心.常规的速度分析方法在大炮检距、地层界面倾斜或弯曲、盐下及深部多层介质等情况下精度不高,影响到地震成像效果与解释结果的可靠性.为解决这个问题,采用了一套叠前时间偏移速度场建立的新方法:初始偏移速度求取和双谱法高密度逐点速度分析,即通过合理的参数提取和速度计算,提高动校正精度,基本消除各向异性影响.把获得的速度和各向异性参数作为Kirchhoff叠前时间偏移的基本参数进行叠前时间偏移处理,从而提高叠前偏移成像精度.通过在东濮凹陷BM和MC地区的实际应用取得了较好的效果.     

共反射角叠前偏移成像研究及应用

共偏移距道集已被广泛地应用于地震速度建模及振幅随偏移距变化(AVO)的研究中,但复杂构造及射线多路径产生的共偏移距道集不保幅性等一系列缺陷给AVO研究带来很大的困难.共反射角道集包含有能反映地下速度和岩性变化的信息,更有利于速度模型优化、地震振幅属性分析及地下岩性和断裂的研究.本文通过研究共反射角深度偏移方法和理论,完善了基于目标的共反射角深度偏移技术,提出了获得相对保幅共反射角道集方法.该方法克服了共偏移距域道集在复杂介质中遇到的困难,更能有效地反映波场和地质结构方面的信息.通过理论模型数据进行了试算,并采用实际地震数据对此方法进行了验证,在陡倾角成像方面取得较好效果.     

面向目标的合成曲面波叠前深度偏移及其应用

面向目标的控制照明叠前深度偏移属于面炮偏移方法的一种特殊情况.通过对目标区域波场照射方向的控制,实现波场在目的层的最佳入射,提高目标区域成像质量.将目的层定义的目标合成算子外推到地表形成地表合成算子,应用地表合成算子进行波面源和记录的合成,最后通过地表合成算子的一系列旋转,实现旋转控制照明叠前深度偏移.本文系统阐述了面向目标的合成曲面波控制照明叠前深度偏移方法的基本原理和实现方法,通过数值模型试算验证了该方法的有效性,最后将其应用到某探区实际资料的处理中,并进行了实际资料的应用效果分析,总结了其在实际资料应用中的特点.     

Bayesian Markov chain Monte Carlo inversion for anisotropy of PP- and PS-wave in weakly anisotropic and heterogeneous media

A single set of vertically aligned cracks embedded in a purely isotropic background may be considered as a long-wavelength effective transversely isotropy (HTI) medium with a horizontal symmetry axis. The crack-induced HTI anisotropy can be characterized by the weakly anisotropic parameters introduced by Thomsen. The seismic scattering theory can be utilized for the inversion for the anisotropic parameters in weakly anisotropic and heterogeneous HTI media. Based on the seismic scattering theory, we first derived the linearized PP- and PS-wave reflection coefficients in terms of P- and S-wave impedances, density as well as three anisotropic parameters in HTI media. Then, we proposed a novel Bayesian Markov chain Monte Carlo inversion method of PP- and PS-wave for six elastic and anisotropic parameters directly. Tests on synthetic azimuthal seismic data contaminated by random errors demonstrated that this method appears more accurate, anti-noise and stable owing to the usage of the constrained PS-wave compared with the standards inversion scheme taking only the PP-wave into account.     

基于叠前全方位角道集方位振幅梯度各向异性变化的HTI裂缝介质油气检测方法与技术

高角度裂缝介质的反射振幅梯度是随方位变化的,常规AVO分析只能适应层状各向同性介质地下地层含油气性检测,很难适应HTI裂缝各向异性介质地层的油气检测.为此,本文提出了基于叠前全方位角道集方位振幅梯度各向异性变化的HTI裂缝介质油气检测方法,推导出以方位角为变量的方位振幅梯度变化函数,并以之为参变量进一步推导出以入射角为变量的,随方位变化而变化的双向振幅响应强度变化函数,同时推导出方位油气指示因子.通过变量拆分法先固定方位方向,通过该方位角道集振幅随入射角的变化求解该方位振幅梯度,继而求出该方位的油气指示因子;依次类推,可求出其余方位的油气指示因子.如此可求出所有方位的油气指示因子,进而可分析含油气指示敏感性随方位的变化,优选油气指示最敏感的方位作为最终的油气预测结果即可.实际工区应用结果表明,本方法预测结果可靠精度高,可为油气勘探开发提供有效的技术支持.

     

轴对称各向异性介质波动方程深度偏移的对称非平稳相移方法

由所建立的三维qP波相速度表示式出发,导出并解析求解各向异性介质中的频散方程,得到三维各向异性介质中的相移算子,进而将以相移算子为基础的对称非平稳相移方法推广到各向异性介质,发展了一个三维各向异性介质的深度偏移方法. 文中使用的各向异性介质的速度模型与现行的各向异性构造的速度估计方法一致,将各向同性、弱各向异性及强各向异性统一在一个模型中. 所建立的各向异性介质对称非平稳相移波场延拓算子可以同时适应速度及各向异性参数横向变化;文中给出的算例虽然是针对二维VTI介质的,但所提出的算法同样适用于三维TI介质.     

Prestack exploding reflector modelling and migration for anisotropic media

The double‐square‐root equation is commonly used to image data by downward continuation using one‐way depth extrapolation methods. A two‐way time extrapolation of the double‐square‐root‐derived phase operator allows for up and downgoing wavefields but suffers from an essential singularity for horizontally travelling waves. This singularity is also associated with an anisotropic version of the double‐square‐root extrapolator. Perturbation theory allows us to separate the isotropic contribution, as well as the singularity, from the anisotropic contribution to the operator. As a result, the anisotropic residual operator is free from such singularities and can be applied as a stand alone operator to correct for anisotropy. We can apply the residual anisotropy operator even if the original prestack wavefield was obtained using, for example, reverse‐time migration. The residual correction is also useful for anisotropic parameter estimation. Applications to synthetic data demonstrate the accuracy of the new prestack modelling and migration approach. It also proves useful in approximately imaging the Vertical Transverse Isotropic Marmousi model.     

叠前偏移技术在中原复杂断块区的应用

随着油气勘探开发的不断深入及相关学科的发展,复杂地质构造成像与地震岩性成像已成为急需解决的课题.针对中原复杂断块区地震资料的特点,对速度场的建立、叠前偏移中关键参数的选取以及偏移方法展开了深入细致的研究.通过叠前偏移技术在中原油田的应用,结果表明了该技术的有效性.     

单程波叠前深度偏移中的界面深度问题研究

单程波深度偏移计算中,两条主要因素影响到反射层的正确定位,一是算子带来的子波相位变化,二是炮点子波脉冲延迟.本文首先r推导了单程波算子导致的相位变化,并且介绍了一种比水平反射层模型偏移验证方法更简单的脉冲叠加验证方法,并用该方法用脉冲试验对比了单程波偏移相位的变化和改正后的结果,子波延迟导致的反射层深度的变化和改正后结...     

黏声介质平面波有限差分叠前深度偏移及在莺歌海盆地的应用

莺琼盆地诸探区中存在底劈现象,深层气源产生的气体沿底劈产生的裂隙通道向上漫溢.漫溢过程中,一是充填在遇到的砂体中形成气藏;二是弥漫在上溢通道中,使得通道中的纵波速度发生变化,进而纵波波阻抗差异变小,反射变弱.另外,通道中气体的存在,会加强地层的吸收衰减,使得地震波振幅变弱、高频成分损失导致同相轴分辨率降低.利用OBC数据进行多波地震勘探和利用黏声介质的叠前深度偏移都是改善模糊区成像质量的重要方法技术.为此,本文提出用黏声介质平面波有限差分法叠前深度偏移成像方法改善气体充填区域的成像质量.黏声介质成像目的是补偿地震波的吸收衰减;平面波偏移成像目的是适应海上单炮数量巨大,提高波动方程叠前深度偏移成像的效率;有限差分法叠前偏移的目的是适应该区浅层气分布局域性极强、Q值的空间变化大的情况.在莺歌海某探区的实际数据上的黏声介质平面波有限差分叠前深度偏移试验证明,本方法是改善模糊区成像质量的较为有效的途径.     

各向异性介质的矢量波场分离与应用

针对裂缝各向异性介质,本文提出一种非正交假设下的矢量波场分离方法.本文首先对多分量地震勘探中常见的波型泄漏现象进行了数学描述,提出在纵、横波波场分离的同时应该考虑恢复纵、横波的矢量振幅.为了对裂缝方位角与各向异性系数进行定量预测,本文将矢量波场分离拆分成三个步骤来实施：第一步,用Z、R两分量的仿射坐标系变换分离ZR平面内的P波投影与SV波;第二步,用ZR平面内的P波投影与T分量的仿射坐标系变换分离P波与SH波;第三步,用纯净的SV波与SH波的成像剖面分离快慢横波,并预测裂缝发育参数.模型数据与实际数据的试验结果表明,本文提出的纵、横波波场分离方法能够获得完整的矢量振幅信息,并提供裂缝预测的精度.

     

地震叠前时间偏移的一种图形处理器提速实现方法

新近发展的图形处理器（GPU,Graphic Processing Unit）通用计算技术,现已日趋实用成型,并获得诸多应用领域的广泛关注.对油气勘探专项资料处理技术的运用而言,概因GPU与中央处理器（CPU）的计算性能的甚大差异,致使GPU这一通用计算技术在石油工业中的应用研究正在有效开展.本文仅借助于油气勘探中广泛使用的叠前时间偏移,旨在于扼要阐明其基于GPU应用的有效性;文中还提出一种利用GPU实现地震叠前时间偏移的软件构件方法,并针对非对称走时叠前时间偏移所拓展的应用软件提供一种具体实现架构.与以往用个人计算机（PC,Personal Computer）或者PC集群所用的叠前时间偏移相比,本文方法可甚大地提高计算效率,从而在石油物探资料处理中可显著地节约计算成本和维护费用.文中实际例证也表明,基于GPU进行高性能并行计算,当是适应目前石油工业中大规模计算需求的一个重要发展途径.     

Generalized migration in frequency-wavenumber domain (MGF-K) in anisotropic media

In this paper, the background of MGF-K migration in dual domain (wavenumber-frequency K-F and space-time) in anisotropic media is presented. Algorithms for poststack (zero-offset) and prestack migration are based on downward extrapolation of acoustic wavefield by shift-phase with correction filter for lateral variability of medium’s parameters. In anisotropic media, the vertical wavenumber was determined from full elastic wavefield equations for two dimensional (2D) tilted transverse isotropy (TTI) model. The method was tested on a synthetic wavefield for TTI anticlinal model (zero-offset section) and on strongly inhomogeneous vertical transverse isotropy (VTI) Marmousi model. In both cases, the proper imaging of assumed media was obtained.     

2.5D modelling, inversion and angle migration in anisotropic elastic media

2.5D modelling approximates 3D wave propagation in the dip‐direction of a 2D geological model. Attention is restricted to raypaths for waves propagating in a plane. In this way, fast inversion or migration can be performed. For velocity analysis, this reduction of the problem is particularly useful. We review 2.5D modelling for Born volume scattering and Born–Helmholtz surface scattering. The amplitudes are corrected for 3D wave propagation, taking into account both in‐plane and out‐of‐plane geometrical spreading. We also derive some new inversion/migration results. An AVA‐compensated migration routine is presented that is simplified compared with earlier results. This formula can be used to create common‐image gathers for use in velocity analysis by studying the residual moveout. We also give a migration formula for the energy‐flux‐normalized plane‐wave reflection coefficient that models large contrast in the medium parameters not treated by the Born and the Born–Helmholtz equation results. All results are derived using the generalized Radon transform (GRT) directly in the natural coordinate system characterized by scattering angle and migration dip. Consequently, no Jacobians are needed in their calculation. Inversion and migration in an orthorhombic medium or a transversely isotropic (TI) medium with tilted symmetry axis are the lowest symmetries for practical purposes (symmetry axis is in the plane). We give an analysis, using derived methods, of the parameters for these two types of media used in velocity analysis, inversion and migration. The kinematics of the two media involve the same parameters, hence there is no distinction when carrying out velocity analysis. The in‐plane scattering coefficient, used in the inversion and migration, also depends on the same parameters for both media. The out‐of‐plane geometrical spreading, necessary for amplitude‐preserving computations, for the TI medium is dependent on the same parameters that govern in‐plane kinematics. For orthorhombic media, information on additional parameters is required that is not needed for in‐plane kinematics and the scattering coefficients. Resolution analysis of the scattering coefficient suggests that direct inversion by GRT yields unreliable parameter estimates. A more practical approach to inversion is amplitude‐preserving migration followed by AVA analysis. SYMBOLS AND NOTATION A list of symbols and notation is given in Appendix D .     

叠前三参数非高斯反演方法研究

针对地球物理反演中广泛采用的"噪声高斯分布假设",本文研究了叠前地震资料中噪声的非高斯分布特征,提出了针对非高斯噪声的地震叠前非高斯反演概念和思想,构造了能同时压制高斯和非高斯噪声的混合范数作为反演目标函数,采用改进的Powell算法进行求解,有效地抑制了叠前地震资料中的高斯和非高斯混合噪声.模型试算和实际地震数据的反演结果验证了方法的正确性和算法的可靠性.     

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.