子波拉伸校正

依赖于偏移距的反射波调谐是AVO分析的不利因素.无论动校正还是偏移,都会引起子波拉伸、频谱向低频移动.在频率域对动校正或偏移后的地震数据进行反拉伸校正是本文消除子波拉伸采用的方法.从射线参数时距方程出发推导的地震映射压缩因子与反射角存在较精确的余弦关系.角度道中动校正或偏移子波拉伸因子是反射角余弦的倒数.用无拉伸子波频...     

基于角度域转换波的叠前深度偏移

在偏移速度分析领域,共成像点道集对偏移速度分析(MVA)而言是非常重要的.目前,用于偏移速度分析的共成像点道集主要有偏移距域共成像点道集(ODCIG)和角度域共成像点道集(ADCIG).由于ODCIG是一种能量聚焦型道集,且在复杂介质条件下存在运动学假象,使其在MVA中的应用受到限制.ADCIG的出现解决了这些问题,它能够适应射线传播的多路径现象,避免假象的产生,波动方程偏移得到的ADCIG被证明是没有假象的道集,也被认为是当前最为合理的道集.论文在CMP域,利用双平方根算子对记录波场进行反向延拓,因为双平方根算子偏移具有倾角假频少、边界处理简单、无需求取震源子波、无需考虑偏移孔径问题以及计算效率高等特点;在频率-波数域将偏移距信息映射到角度域得到ADCIG.ADCIG的提取过程实际是转化了地震数据中的多偏移距信息,本质上,它仍旧是对地震数据中多偏移距信息的体现.最后论文将ADCIG道集应用在SEG/EAGE岩丘模型中,结果表明,不同反射角下的ADCIG可以对地下不同的区域进行成像,且角度域成像具有地震波成像剖面分辨率高,边界干扰较小等特点.     

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.     

串珠状溶洞模型介质波动方程正演与偏移

为了揭示溶洞储层的地震波场特征,该文采用相移加插值波场延拓算子,该算子能适应介质速度横向变化和纵向变化、对地层无倾角限制、保振幅且可以避免层间多次波的产生.然后用该算子对根据某地区奥陶系储层溶洞的地质特征所设计的五个串珠状溶洞地质模型进行正演和偏移,并分析波场特征.溶洞储层模型数值模拟的结果揭示了在不同大小、形状、间距、分布位置等情况下溶洞地震波场特征,得出了关于串珠状溶洞介质地震波场特征的一些有意义的结论和认识.     

薄互层地震成像中高分辨率处理方法

地震子波在叠前时间偏移前、偏移过程中以及偏移后具有不同特性和非稳态性,使得基于子波压缩原理的反褶积和基于绕射叠加原理的叠前时间偏移不能有效地提高薄互层地震分辨率.本文基于叠前时间偏移前后以及偏移过程中地震子波频率特性的分析,联合三种高分辨率处理方法对薄互层进行成像,即偏移前CMP道集应用反Q滤波补偿高频衰减、偏移过程中应用最优加权Kirchhoff叠前时间偏移降低高频损失、偏移后在CRP道集上应用子波调谐反褶积拓展频带.数值分析和实例证明,本文采用的三种高分辨率处理方法是必要的,对刻画薄互层厚度与边界能够取得好的效果,利于后续的岩性储层预测与AVO/AVP/AVA反演.     

基于虚源估计的复杂上覆地层下地震相干成像

在上覆地层比较复杂的情况下,常规地震勘探方法常常难以得到好的成像.本文研究了基于地震相干避开复杂上覆地层对地震波的影响,利用VSP数据估计地震虚源直接对目的地层进行成像的方法.在地震相干成像过程中,震源子波对分辨率有比较大的影响,尤其是存在薄层的条件下,两个非常近的反射同相轴将无法辨认.利用估计出虚源地震子波的性质,对...     

地震正演模拟在高分辨率隐伏断层地震勘探中的应用

应用波动方程有限差分方法人工合成地震记录进行城市隐伏断层的地震勘探.采用适当的差分算法、震源子波以及有效地边界条件和频散消除方法来提高正演模拟的精度和分辨率.结果表明地震数值模拟可以用来分析地层厚度、断层倾角、断层深度以及断裂带宽度等参数对地震记录的影响;通过实际试验数据和正演模拟的合成单炮地震记录的对比,可以快速判断断层的大致位置和断裂带的大致范围以及目标地层的大致深度.该方法能有效辅助实际野外工作中的数据采集参数的估计,提高勘探效率和精度.     

基于Poynting矢量和方向行波波场分离的逆时偏移成像条件

叠前逆时偏移在解决陡倾角构造和复杂速度模型成像上展示出了极佳的优越性,但是低频噪声的存在严重影响了成像的质量.Poynting矢量的方向代表了介质中地震波的传播方向,根据Poynting矢量可以计算出反射角并且可将地震波场分离成上行波、下行波.本文提出了一种新的成像条件,同方向上下行波互相关成像噪声和大角度成像噪声可以得到较好的压制.相比于常规的互相关成像条件,该方法简单易行,所需额外的计算量和存储量极小,将该成像条件应用在Marmousi模型上,偏移结果显示低频噪声得到很好的压制.     

用于深度域地震剖面衰减与频散补偿的反Q滤波方法

根据地震波在非弹性介质中的传播规律，本文提出了一种在深度域地震剖面进行反Q滤波的新方法. 在深度域的Q滤波算子符合地震波在衰减介质中的传播规律，不仅考虑了介质吸收对地震波振幅的影响，而且还保证了所造成的波形畸变满足因果规律，即地震体波具有某种频散性质. 利用该方法处理了2条总长度约60km的某浅海地区叠后深度偏移地震剖面. 合成记录剖面的正演和反演计算结果表明，在对地震剖面进行深度域反Q滤波之后 ，不仅达到了压缩中、深部目的层子波宽度提高分辨率和信噪比的目的，而且保持了原始地震剖面的整体形态和能量分布.     

零偏移距VSP资料层Q反演及其应用研究(英文)

地层品质因子Q的可用于地震资料高分辨率处理,而从VSP资料下行直达波更容易获取准确的地层品质因子。通过对零偏移距VSP资料的监控子波和下行初至波的频谱进行综合分析,仿照Ricker子波频谱的表达式,本文提出了震源子波频谱新的表达式。在震源子波频谱新的表达式基础上,我们介绍了改进的频谱拟合法和改进的谱比法的层Q值反演方法及相应的处理流程。基于本文提出的层Q值反演方法,利用实际的零偏移距VSP资料的下行直达波,反演稳定的层Q值,并用于零偏移距VSP资料及井旁地面地震资料的反Q滤波振幅补偿处理,提高了地震资料的分辨率。     

The form of the reflection operator and extended image gathers for a dipping plane reflector in two space dimensions

The reflection operator for a simple flat‐lying interface can be thought of as the set of all its plane‐wave reflection coefficients or as the set of virtual surveys with sources and receivers along the interface. When there is dip, however, it is necessary to include the varying effects of propagation between the virtual‐survey level and the interface. Hence, step one in this paper is to derive the reflection operator for a dipping plane interface as observed at a datum level some distance away. The key assumption is that the aperture at the datum level is sufficient to characterize the reflector properties around a particular point. This translates into an assumption that the dip is moderate, though no explicit small‐angle approximation is required. The second step is to find the apparent reflection operator that would relate data that have been extrapolated from the datum towards and possibly beyond the reflector using an assumed migration velocity. This apparent reflection operator is closely related to extended common‐image gathers. The apparent reflection operator may be analysed asymptotically in terms of rays and other signals, shedding light on the structure of extended image gathers. In keeping with the virtual‐survey idea, the results are considered in a subsurface space‐time or slowness‐time domain at various extrapolation levels around the interface. An important distinction is drawn between using subsurface midpoint‐offset coordinates and the wavefield coordinates of the incident and reflected waves. The latter reveal more clearly the effects of dip, because they lead to a more asymmetric apparent reflection operator. Properties such as an up‐dip shift of a traveltime minimum and its associated curvature theoretically provide information about the reflector location and dip and the migration‐velocity error. The space‐time form of the reflection operator can be highly intricate around the offset‐time origin and it was described for a simple flat interface in a background paper. To avoid a layer of mathematics, the reflection‐operator formulas presented here are in the intermediate space‐frequency domain. They are analysed by considering their stationary‐phase and branch‐point high‐frequency contributions. There is no Born‐like assumption of weak reflector contrast and so wide‐angle, total reflection and head‐wave effects are included. Snell’s law is an explicit part of the theory. It is hoped that the work will therefore be a step towards the goal of unifying amplitude‐versus‐offset, imaging and waveform inversion.     

基于目标区的局部角度域方向照明分析及其在偏移成像中的应用

叠前深度偏移已成为近年来地震偏移成像领域广泛应用的技术之一,其中复杂盐丘下方目标区域结构的成像始终是偏移成像中较难解决的问题.局部角度域波场分解可以提供在空间和方向上的双重局部化信息,因而这一技术被广泛地应用在方向照明分析、成像振幅校正等方面.本文在采用局部指数标架小波束进行角度域方向照明分析的基础上,研究采集系统对复杂盐丘下部层状结构成像质量的影响;同时通过分析目标区对应于相对地表采集系统分布的照明能量,确定叠前炮集数据中对盐下目标区成像起重要贡献的部分,并将这些数据用来对目标区成像,从而达到提高盐下结构成像质量的目的.本文将二维SEG-EAGE盐丘模型中盐下反射体作为目标区,分别计算其照明分析和由照明能量分布确定的炮集数据对目标区的偏移成像结果,同时通过与成像振幅校正前后的成像结果对比,说明了该方法对提高目标区结构成像质量的有效性.     

频率-空间域有限差分法叠前深度偏移

为了处理横向强变速介质中的深度成像问题,本文提出一种基于共炮道集的优化系数的傍轴近似方程叠前深度偏移算子,并在基于反射系数估算的成像条件下,可实现叠前深度偏移成像.该算子具有方程阶数低且能对陡倾角成像的特征,并采用有限差分法波场延拓,能适应速度场的任意变化.当在频率-空间域进行计算时,相对于纯粹的时间-空间域有限差分算法有计算效率高、成像方便的优点.脉冲响应测试和对Marmousi模型进行的叠前深度偏移结果表明,该偏移方法在强横向变速情况下具有非常好的成像效果.     

3D ACOUSTIC REVERSE-TIME MIGRATION1

Acoustic reverse-time finite-difference migration for zero-offset data is extended from two- to three-dimensional media. The formulation is based on the full three-dimensional acoustic wave equation and so has no dip restrictions and it involves extrapolation in a velocity distribution variable in three dimensions. The algorithm is demonstrated by successful migration of synthetic data sets for three models: a point diffractor, an oblique pinch-out, and a dome overlying a planar reflector.     

Finding the strike direction of fractures using GPR

GPR reflection energy varies with antenna orientation relative to the strike and dip of the reflector. This directional dependence of GPR responses was investigated through numerical experiments and was used to estimate the azimuth of fractures and joints. Three antenna configurations were considered in this study: perpendicular-broadside (YY mode), parallel-broadside (XX mode) and cross-polarization (YX mode). The reflection energy in the cross-polarization mode shows a shape characteristic similar to the strike, regardless of the dip angle. Those in the other two modes show quite different amplitudes from the strike, depending on the dip angle.  We have developed a strike-direction-finding scheme using data obtained from the three different modes for the same survey line. The azimuth angle of each reflector was displayed in colour on the GPR profile. This scheme was applied to a field survey at a granite quarry in southern Korea. The GPR profiles showed different images of the reflectors depending on the antenna configuration. The estimated azimuths of reflectors obtained using our scheme matched fairly well with those of known fractures and joints.     

STACKING OF P-SV SEISMIC REFLECTION DATA USING DIP MOVEOUT1

The moveout of P-SV mode-converted seismic reflection events in a common-midpoint gather is non-hyperbolic. This is true even if the medium has constant P- and SV-wave velocities. Furthermore, reflection-point smear occurs even along horizontal reflectors. These effects reduce the resolution of the zero-offset stack. In such a medium, the generalization of the dip moveout transformation to P-SV data can be calculated analytically. The resulting P-SV dip moveout operators solve the problem of reflection-point smear, and image any reflector regardless of dip or depth. The viability of this technique is demonstrated on synthetic and field data.     

基于倾角-偏移距域道集的绕射波成像

地震绕射波是地下非连续性地质体的地震响应,绕射波成像对地下断层、尖灭和小尺度绕射体的识别具有重要的意义.在倾角域共成像点道集中,反射波同相轴表现为一条下凸曲线,能量主要集中在菲涅耳带内,绕射波能量则比较发散.由于倾角域菲涅耳带随偏移距变化而存在差异,因此本文提出一种在倾角-偏移距域道集中精确估计菲涅耳带的方法,在各偏移距的倾角域共成像点道集中实现菲涅耳带的精确切除,从而压制反射波.在倾角-偏移距域道集中还可以分别实现绕射波增强,绕射波同相轴相位校正,因此能量弱的绕射波可以清晰地成像.在倾角域共成像点道集中,反射波同相轴的最低点对应于菲涅耳带估计所用的倾角,因此本文提出一种在倾角域共成像点道集中直接自动拾取倾角场的方法.理论与实际资料试算验证了本文绕射波成像方法的有效性.     

Poststack diffraction imaging using reverse‐time migration

We propose a method for imaging small‐scale diffraction objects in complex environments in which Kirchhoff‐based approaches may fail. The proposed method is based on a separation between the specular reflection and diffraction components of the total wavefield in the migrated surface angle domain. Reverse‐time migration was utilized to produce the common image gathers. This approach provides stable and robust results in cases of complex velocity models. The separation is based on the fact that, in surface angle common image gathers, reflection events are focused at positions that correspond to the apparent dip angle of the reflectors, whereas diffracted events are distributed over a wide range of angles. The high‐resolution radon‐based procedure is used to efficiently separate the reflection and diffraction wavefields. In this study, we consider poststack diffraction imaging. The advantages of working in the poststack domain are its numerical efficiency and the reduced computational time. The numerical results show that the proposed method is able to image diffraction objects in complex environments. The application of the method to a real seismic dataset illustrates the capability of the approach to extract diffractions.     

Diffraction imaging using an adaptive phase filter

As an ideal carrier of high-resolution information, seismic diffraction can be used to clarify and locate small-scale discontinuities or inhomogeneities in the subsurface. However, a diffraction is weak and thus be suppressed by the specular reflection. Furthermore, a diffraction would be destroyed by the conventional imaging method due to the polarity reversal of diffraction. In this paper, we analyse the behaviour of diffraction and reflection. For the image point on a horizontal or oblique reflector, the zone on both sides of the stationary point has the same energy after using a cosine weight function. Based on the behaviour, we propose the adaptive phase filter to adjust the polarity of the energy on both sides, and calculate it through the illumination angle and the reflector dip angle. This method avoids the calculation of the Fresnel zones and can further suppress residual reflection that disturb the diffraction images. Synthetic and field data applications show that the desired imaging results can be obtained by the proposed method. The test results demonstrate that the method is efficient in detecting small-scale discontinuities or inhomogeneities in the subsurface and can provide high-resolution information for seismic interpretation.