共查询到18条相似文献，搜索用时 296 毫秒
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研究与实践表明,对于长偏移距、宽方位地震数据,忽略各向异性会明显降低成像质量,影响储层预测与描述的精度.针对典型的横向各向同性(TI)介质,本文面向深度域构造成像与偏移速度分析的需要,研究基于射线理论的局部角度域叠前深度偏移成像方法.它除了像传统Kirchhoff叠前深度偏移那样输出成像剖面和炮检距域的共成像点道集,还遵循地震波在成像点处的局部方向特征、基于扩展的脉冲响应叠加原理获得入射角度域和照明角度域的成像结果.为了方便快捷地实现TI介质射线走时与局部角度信息的计算,文中讨论和对比了两种改进的射线追踪方法:一种采用从经典各向异性介质射线方程演变而来的由相速度表征的简便形式;另一种采用由对称轴垂直的TI(即VTI)介质声学近似qP波波动方程推导出来的射线方程.文中通过坐标旋转将其扩展到了对称轴倾斜的TI(即TTI)介质.国际上通用的理论模型合成数据偏移试验表明,本文方法既适用于复杂构造成像,又可为TI介质深度域偏移速度分析与模型建立提供高效的偏移引擎. 相似文献
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本文通过选取合适的叠前时间偏移软件,对两块三维地震资料进行偏移成像试验,验证叠前时间偏移中影响偏移成像效果的几个主要因素.该软件偏移算法的核心技术是弯曲射线偏移处理,这不同于工业界常用的直射线假设.偏移速度是偏移成像好坏的主要因素,通过迭代进行偏移、速度分析,使共成像点道集拉平,从而实现构造的准确成像;偏移孔径也是影响偏移成像的一个关键参数,其选取与成像目标层的倾斜角、深度、速度等有关;反假频参数对偏移成像效果有一定影响,是偏移中需要考虑的因素之一. 相似文献
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《应用地球物理》2019,(3)
变偏移距VSP反射波射线路径是不对称、覆盖次数也不均匀,因此通常使用偏移速度分析、层析反演建立准确的2D、3D速度场,尤其角度域共成像道集最适合偏移速度分析,通常拾取其剩余曲率更新速度,建立准确的速度场。为了建立高精度速度模型,本文推导了VSP角度域共成像道集剩余深度与旅行时残差的关系,用最小二乘求解更新速度,建立了一个四参数层析反演方程,包括地层倾角、入射角、剩余深度、灵敏度矩阵等四个参数。在角度域中将反射波分解为上行、下行两个透射波计算其旅行时。采用"逐步-累加"方式进行复杂地表叠前深度偏移ωx。通过叠前深度偏移得到偏移距域共成像道集,拾取剩余深度;在叠加成像剖面上拾取层位获取地层倾角;利用Runge-Kutta射线追踪计算地层反射点到检波点的射线路径,确定入射角,再计算地层反射点到复杂地表的射线路径;将偏移距域剩余深度映射为角度域,建立层析方程并求解。经模型和塔里木盆地"双复杂"地区Walkaway VSP实测资料验证表明,推导的层析反演方程能建立较准确的速度模型,偏移算法能适应复杂地表。 相似文献
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Thomsen各向异性参数的求取对于正确的时深转换和深度域偏移成像处理至关重要。相比其它各向异性参数估算方法,从VSP资料中更容易获取准确的各向异性参数用于地面地震偏移成像。本文分析研究了利用Walkaway VSP资料估算VTI介质Thomsen各向异性参数的方法,该方法基于VTI介质近偏移距动校正公式利用Walkaway VSP近偏移距初至信息求取各向异性参数δ;基于各向异性介质纵波速度Thomsen近似公式采用射线追踪时差扫描方法求取各向异性参数ε。数值模型正演表明利用该方法估算的各向异性参数误差较小。利用塔里木盆地8个方位的Walkaway VSP实际资料求取了该区深度域Thomsen各向异性参数ε和δ值,同时结合地面三维地震资料建立了较为准确的各向异性深度一速度模型用于叠前深度偏移成像,进一步提高了碳酸盐岩储层的成像精度,减小了目标地质体的深度误差。 相似文献
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各向异性射线理论基础上的局部角度域叠前深度偏移方法能够为深度域构造成像与基于角道集的层析反演提供有力支撑,但是对于复杂地质构造而言,高斯度叠前深度偏移在不失高效、灵活等特点的情况下,具有明显的精度优势.为此,本文研究局部角度域理论框架下的高斯束叠前深度偏移方法.为提高算法效率与实用性,文中讨论了一种从经典弹性参数表征的各向异性介质运动学和动力学射线方程演变而来的由相速度表征的简便形式,并提出了一种比较经济的各向异性高斯束近似合成方案.结合地震波局部角度域成像原理,讨论一种适合高斯束偏移的角度参数计算方法.国际上通用的理论模型合成数据试验表明：相比局部角度域Kirchhoff叠前深度偏移成像方法,本文方法具有更高的成像精度与抗噪能力,既适用于复杂构造成像,也可为TI介质深度域偏移速度分析与模型建立提供高效的偏移引擎. 相似文献
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是否能够正确地建立深度域三维速度模型是三维叠前深度偏移成败的关键 .本文根据Deregowski循环 ,利用叠前深度域地震成像对速度模型变化的敏感性 ,采用偏移迭代逐次逼近最佳成像速度 ,研究开发了一套快捷有效的三维叠前深度偏移深度域速度模型建立技术 .借鉴时间域CDP(共深度点 )道集上常规叠加速度分析的策略 ,在深度域CRP(共反射点 )道集上 ,提出剩余慢度平方谱的概念并建立相应的实现技术 .导出深度域中均方根速度与层速度之间的关系 ;按照串级偏移原理确定偏移循环过程中初始速度、剩余速度及修改后速度之间的关系 ;采用蒙特卡洛非线性优化算法实现从剩余慢度平方谱中自动拾取层速度 ,讨论了其地质速度约束条件和蒙特卡洛非线性优化的收敛准则 ,使得所拾取的层速度模型具有合理的地质意义并获得最佳偏移成像效果 .SEG EAGE理论模型数值试算验证了方法的有效性 ,在海拉尔盆地霍多莫尔工区 ,5 8km2 三维资料的速度模型建立并获得满意的三维叠前深度偏移成像 . 相似文献
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A robust approach to time‐to‐depth conversion and interval velocity estimation from time migration in the presence of lateral velocity variations 
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下载免费PDF全文 Sergey Fomel 《Geophysical Prospecting》2015,63(2):315-337
The problem of conversion from time‐migration velocity to an interval velocity in depth in the presence of lateral velocity variations can be reduced to solving a system of partial differential equations. In this paper, we formulate the problem as a non‐linear least‐squares optimization for seismic interval velocity and seek its solution iteratively. The input for the inversion is the Dix velocity, which also serves as an initial guess. The inversion gradually updates the interval velocity in order to account for lateral velocity variations that are neglected in the Dix inversion. The algorithm has a moderate cost thanks to regularization that speeds up convergence while ensuring a smooth output. The proposed method should be numerically robust compared to the previous approaches, which amount to extrapolation in depth monotonically. For a successful time‐to‐depth conversion, image‐ray caustics should be either nonexistent or excluded from the computational domain. The resulting velocity can be used in subsequent depth‐imaging model building. Both synthetic and field data examples demonstrate the applicability of the proposed approach. 相似文献
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BRUCE J. VERWEST 《Geophysical Prospecting》1989,37(2):149-166
The study of wave propagation in media with elliptical velocity anisotropy shows that seismic energy is focused according to the horizontal component of the velocity field while the vertical component controls the time-to-depth relation. This implies that the vertical component cannot be determined from surface seismic velocity analysis but must be obtained using borehole or regional geological information. Both components of the velocity field are required to produce a correctly focused depth image. A paraxial wave equation is developed for elliptical anisotropic wave propagation which can be used for modelling or migration. This equation is then transformed by a change of variable to a second paraxial equation which only depends on one effective velocity field. A complete anisotropic depth migration using this transformed equation involves an imaging step followed by a depth stretching operation. This allows an approximate separation or splitting of the focusing and depth conversion steps of depth migration allowing a different velocity model to be used for each step. This split anisotropic depth migration produces a more accurate result than that obtained by a time migration using the horizontal velocity field followed by an image-ray depth conversion using the vertical velocity field. The results are also more accurate than isotropic depth migration and yield accurate imaging in depth as long as the lateral variations in the anisotropy are slow. 相似文献
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P. HUBRAL 《Geophysical Prospecting》1977,25(4):738-745
Using an elementary theory of migration one can consider a reflecting horizon as a continuum of scattering centres for seismic waves. Reflections arising at interfaces can thus be looked upon as the sum of energy scattered by interface points. The energy from one point is distributed among signals upon its reflection time surface. This surface is usually well approximated by a hyperboloid in the vicinity of its apex. Migration aims at focusing the scattered energy of each depth point into an image point upon the reflection time surface. To ensure a complete migration the image must be vertical above the depth point. This is difficult to achieve for subsurface interfaces which fall below laterally in-homogeneous velocity media. Migration is hence frequently performed for these interfaces as well by the Kirchhoff summation method which systematically sums signals into the apex of the approximation hyperboloid even though the Kirchhoff integral is in this case not strictly valid. For a multilayered subsurface isovelocity layer model with interfaces of a generally curved nature this can only provide a complete migration for the uppermost interface. Still there are various advantages gained by having a process which sums signals consistently into the minimum of the reflection time surface. The position of the time surface minimum is the place where a ray from the depth point emerges vertically to the surface. The Kirchhoff migration, if applied to media with laterally inhomogeneous velocity, must necessarily be followed by a further time-to-depth migration if the true depth structure is to be recovered. Primary normal reflections and their respective migrated reflections have a complementary relationship to each other. Normal reflections relate to rays normal to the reflector and migrated reflections relate to rays normal to the free surface. Ray modeling is performed to indicate a new approach for simulating seismic reflections. Commonly occuring situations are investigated from which lessons can be learned which are of immediate value for those concerned with interpreting time migrated reflections. The concept of the ‘image ray’ is introduced. 相似文献
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在反射地震转换波资料处理中,准确求取共转换点一直是一个难题,采用叠前时间偏移技术能避免共转换点道集的抽取,而且能够使转换波归位到真正的反射点上,实现准确成像.本文针对火山岩地震屏蔽层的转换波成像问题,通过对转换波共近似转换点道集进行速度分析,建立了转换波叠前时间偏移的初始速度场,通过速度扫描和纵、横波速度比值扫描确定最佳的偏移速度场和纵、横波速度比值,实现了在火山岩高速层覆盖区域的转换波偏移成像.实际资料的成像结果表明,本文采用的近似转换点计算以及转换波叠前时间偏移方法是有效的. 相似文献
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Estimation of Thomsen＇s anisotropic parameters is very important for accuratetime-to-depth conversion and depth migration data processing. Compared with othermethods, it is much easier and more reliable to estimate anisotropic parameters that arerequired for surface seismic depth imaging from vertical seismic profile （VSP） data, becausethe first arrivals of VSP data can be picked with much higher accuracy. In this study, wedeveloped a method for estimating Thomsen＇s P-wave anisotropic parameters in VTImedia using the first arrivals from walkaway VSP data. Model first-arrival travel times arecalculated on the basis of the near-offset normal moveout correction velocity in VTI mediaand ray tracing using Thomsen＇s P-wave velocity approximation. Then, the anisotropicparameters 0 and e are determined by minimizing the difference between the calculatedand observed travel times for the near and far offsets. Numerical forward modeling, usingthe proposed method indicates that errors between the estimated and measured anisotropicparameters are small. Using field data from an eight-azimuth walkaway VSP in TarimBasin, we estimated the parameters 0 and e and built an anisotropic depth-velocity modelfor prestack depth migration processing of surface 3D seismic data. The results showimprovement in imaging the carbonate reservoirs and minimizing the depth errors of thegeological targets. 相似文献
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Improved amplitude preservation for prestack depth migration by inverse scattering theory 总被引：6，自引：1，他引：6
A prestack reverse time-migration image is not properly scaled with increasing depth. The main reason for the image being unscaled is the geometric spreading of the wavefield arising during the back-propagation of the measured data and the generation of the forward-modelled wavefields. This unscaled image can be enhanced by multiplying the inverse of the approximate Hessian appearing in the Gauss–Newton optimization technique. However, since the approximate Hessian is usually too expensive to compute for the general geological model, it can be used only for the simple background velocity model.We show that the pseudo-Hessian matrix can be used as a substitute for the approximate Hessian to enhance the faint images appearing at a later time in the 2D prestack reverse time-migration sections. We can construct the pseudo-Hessian matrix using the forward-modelled wavefields (which are used as virtual sources in the reverse time migration), by exploiting the uncorrelated structure of the forward-modelled wavefields and the impulse response function for the estimated diagonal of the approximate Hessian. Although it is also impossible to calculate directly the inverse of the pseudo-Hessian, when using the reciprocal of the pseudo-Hessian we can easily obtain the inverse of the pseudo-Hessian. As examples supporting our assertion, we present the results obtained by applying our method to 2D synthetic and real data collected on the Korean continental shelf. 相似文献
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复杂构造地震成像主要取决于叠前地震数据品质、偏移速度可靠性和偏移算子成像精度. 库车坳陷异常复杂的近地表条件导致极低信噪比的地震采集数据. 该区逆冲推覆高陡构造刺穿盐体大面积分布, 盐层厚度变化大、顶底面形态复杂, 盐下断裂带破碎、小断块发育, 形成异常复杂的地震成像问题. 本文重点研究三个关键环节:(1)精细的叠前地震预处理研究: 根据该区地震地质复杂性和地震资料特征, 采用一些新的方法技术和技术组合从振幅与时移的大、中、小尺度变化三个层次来解决资料信噪比问题, 重建深部反射信号; (2)三级偏移速度分析研究:利用库车坳陷盐刺穿逆冲推覆构造建模理论及变速成图配套技术解决叠前时间偏移速度场时深转换问题,利用井约束低频速度地震迭代反演技术解决连井层速度场与偏移速度场的融合问题,实现从DMO速度分析、叠前时间偏移速度分析到叠前深度偏移速度分析的有机衔接,建立拓扑结构相对保持的叠前深度偏移速度模型;(3)基于退化Fourier偏移算子的半解析波动方程叠前时间和深度偏移研究, 极大地改善了地震偏移过程中高波数波的成像问题. 通过对库车坳陷大北、博孜、却勒、西秋4和西秋10等复杂高陡构造的叠前时间和深度偏移地震成像处理,取得了较好的应用效果. 相似文献
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Martin Tygel Bjørn Ursin Einar Iversen Maarten V. de Hoop 《Geophysical Prospecting》2012,60(2):201-216
Starting from a given time‐migrated zero‐offset data volume and time‐migration velocity, recent literature has shown that it is possible to simultaneously trace image rays in depth and reconstruct the depth‐velocity model along them. This, in turn, allows image‐ray migration, namely to map time‐migrated reflections into depth by tracing the image ray until half of the reflection time is consumed. As known since the 1980s, image‐ray migration can be made more complete if, besides reflection time, also estimates of its first and second derivatives with respect to the time‐migration datum coordinates are available. Such information provides, in addition to the location and dip of the reflectors in depth, also an estimation of their curvature. The expressions explicitly relate geological dip and curvature to first and second derivatives of reflection time with respect to time‐migration datum coordinates. Such quantitative relationships can provide useful constraints for improved construction of reflectors at depth in the presence of uncertainty. Furthermore, the results of image‐ray migration can be used to verify and improve time‐migration algorithms and can therefore be considered complementary to those of normal‐ray migration. So far, image‐ray migration algorithms have been restricted to layered models with isotropic smooth velocities within the layers. Using the methodology of surface‐to‐surface paraxial matrices, we obtain a natural extension to smooth or layered anisotropic media. 相似文献