共查询到20条相似文献，搜索用时 562 毫秒
1.
Zhang Liyan Liu Yang 《应用地球物理》2006,3(1):18-26
Pseudo-offset migration （POM） is a new method for prestack time migration of converted waves that improves on equivalent-offset migration （EOM）. The mapping of POM is different than EOM but the purpose of the two methods is to map the input samples to the common conversion scatter point （CCSP） gathers. This paper introduces the principles of the two migration methods and model parameter sensitivity tests for both POM and EOM. At large offset-to-depth ratios the hyperbolic approximation, the three-term approximation and the double square root （DSR） equation are used to NMO-correct the mapped POM gathers to obtain more accurate migration velocities. These equations were derived and calculated by small pseudo offset. POM is then used to image complex structure and prestack time migration. 相似文献
2.
基于虚拟偏移距方法的各向异性转换波保幅叠前时间偏移 总被引：2，自引：1，他引：1
In this paper, we use the method of pseudo-offset migration （POM） to complete converted wave pre-stack time migration with amplitude-preservation in an anisotropic medium. The method maps the original traces into common conversion scatter point （CCSP） gathers directly by POM, which simplifies the conventional processing procedure for converted waves. The POM gather fold and SNR are high, which is favorable for velocity analysis and especially suitable for seismic data with low SNR. We used equivalent anisotropic theory to compute anisotropic parameters. Based on the scattering wave traveltime equation in a VTI medium, the POM pseudo-offset migration in anisotropic media was deduced. By amplitude-preserving POM gather mapping, velocity analysis, stack processing, and so on, the anisotropic migration results were acquired. The forward modeling computation and actual data processing demonstrate the validity of converted wave pre-stack time migration with amplitude-preservation using the anisotropic POM method. 相似文献
3.
Xiong Xiaojun He Zhenhua Huang Deji 《应用地球物理》2006,3(1):13-17
Mathematical geophone （MG） and equal-time stacking （ETS） principles are used to implement seismic prestack forward modeling with irregular surfaces using the oneway acoustic wave-equation. This method receives seismic primary reflections from the subsurface using a set of virtual MGs. The receivers can be located anywhere on an irregular observing surface. Moreover, the ETS method utilizes the one-way acoustic wave equation to easily and quickly image and extrapolate seismic reflection data. The method is illustrated using high single-noise ratio common shot gathers computed by numerical forward modeling of two simple models, one with a flat surface and one with an irregular surface, and a complex normal fault model. A prestack depth migration method for irregular surface topography was used to reoroduce the normal fault model with high accuracy. 相似文献
4.
The conventional nonstationary convolutional model assumes that the seismic signal is recorded at normal incidence. Raw shot gathers are far from this assumption because of the effects of offsets. Because of such problems, we propose a novel prestack nonstationary deconvolution approach. We introduce the radial trace （RT） transform to the nonstationary deconvolution, we estimate the nonstationary deconvolution factor with hyperbolic smoothing based on variable-step sampling （VSS） in the RT domain, and we obtain the high-resolution prestack nonstationary deconvolution data. The RT transform maps the shot record from the offset and traveltime coordinates to those of apparent velocity and traveltime. The ray paths of the traces in the RT better satisfy the assumptions of the convolutional model. The proposed method combines the advantages of stationary deconvolution and inverse Q filtering, without prior information for Q. The nonstationary deconvolution in the RT domain is more suitable than that in the space-time （XT） domain for prestack data because it is the generalized extension of normal incidence. Tests with synthetic and real data demonstrate that the proposed method is more effective in compensating for large-offset and deep data. 相似文献
5.
Cauchy priori distribution-based Bayesian AVO reflectivity inversion may lead to sparse estimates that are sensitive to large reflectivities. For the inversion, the computation of the covariance matrix and regularized terms requires prior estimation of model parameters, which makes the iterative inversion weakly nonlinear. At the same time, the relations among the model parameters are assumed linear. Furthermore, the reflectivities, the results of the inversion, or the elastic parameters with cumulative error recovered by integrating reflectivities are not well suited for detecting hydrocarbons and fuids. In contrast, in Bayesian linear AVO inversion, the elastic parameters can be directly extracted from prestack seismic data without linear assumptions for the model parameters. Considering the advantages of the abovementioned methods, the Bayesian AVO reflectivity inversion process is modified and Cauchy distribution is explored as a prior probability distribution and the time-variant covariance is also considered. Finally, we propose a new method for the weakly nonlinear AVO waveform inversion. Furthermore, the linear assumptions are abandoned and elastic parameters, such as P-wave velocity, S-wave velocity, and density, can be directly recovered from seismic data especially for interfaces with large reflectivities. Numerical analysis demonstrates that all the elastic parameters can be estimated from prestack seismic data even when the signal-to-noise ratio of the seismic data is low. 相似文献
6.
A modified method for simulating non-stationary multi-point earthquake ground motion 总被引：1，自引：1，他引：0
A spectral-representation-based algorithm is proposed to simulate non-stationary and stochastic processes with evolutionary power,according to a prescribed non-stationary cross-spectral density matrix. Non-stationary multi-point seismic ground motions at different locations on the ground surface are generated for use in engineering applications. First,a modified iterative procedure is used to generate uniformly modulated non-stationary ground motion time histories which are compatible with the prescribed power spectrum. Then,ground motion time histories are modeled as a non-stationary stochastic process with amplitude and frequency modulation. The characteristic frequency and damping ratio of the Clough-Penzien acceleration spectrum are considered as a function of time in order to study the frequency time variation. Finally,two numerical examples are presented to validate the efficiency of the proposed method,and the results show that this method can be effectively applied to the dynamic seismic analysis of long and large scale structures. 相似文献
7.
Seismic velocity is important to migration of seismic data,interpretation of lithology and lithofacies as well asprediction of reservoir.The information of shear wave velocity is required to reduce the uncertainty for discrimi-nating lithology,identifying fluid type in porous material and calculating gas saturation in reservoir prediction.Based on Zoeppritz equations,a numeral and scanning method was proposed in this paper.Shear wave velocitycan be calculated with prestack converted wave data.The effects were demonstrated by inversion of theoreticaland real seismic data. 相似文献
8.
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. 相似文献
9.
基于三角网格的有限差分法叠后逆时偏移 总被引：1，自引：1，他引：0
Compared with other migration methods, reverse-time migration is based on a precise wave equation, not an approximation, and performs extrapolation in the depth domain rather than the time domain. It is highly accurate and not affected by strong subsurface structure complexity and horizontal velocity variations. The difference method based on triangular grids maintains the simplicity of the difference method and the precision of the finite element method. It can be used directly for forward modeling on models with complex top surfaces and migration without statics preprocessing. We apply a finite difference method based on triangular grids for post-stack reverse-time migration for the first time. Tests on model data verify that the combination of the two methods can achieve near-perfect results in application. 相似文献
10.
Based on arbitrarily wide-angle wave equations,a reverse-time propagation scheme is developed by substituting the partial derivatives of depth and time with central differences. The partial derivative of horizontal direction is replaced with high order difference. The imaging condition is computed by solving the eikonal equations. On the basis of above techniques,a prestack reverse-time depth migration algorithm is developed. The processing exam-ples of synthetic data show that the method can remove unwanted internal reflections and decrease the migration noise. The method also has the advantage of fidelity and is applicable of dip angle reflector imaging. 相似文献
11.
基于共炮偏移的AVO反演 总被引：8，自引：0，他引：8
常规AVO多是利用CMP道集的振幅进行反演。主要有三个方面影响其精度:首先,CMP道集假设地下为水平层状介质,但是实际地下介质多为倾斜地层,地层倾角越大CMP道集的振幅所反映地下介质的位置与实际位置差距就越大。其次,NMO、DMO和反褶积等常规处理流程,都会造成振幅值失真。第三,反演所用的反射系数公式是与入射角有关的量,而欲从CMP道集得到准确的入射角与振幅之间的对应关系,则十分困难。波动方程叠前深度偏移除对复杂介质和陡倾角地层具有较强的成像能力,还可以最大限度的减少常规处理所带来的误差并使振幅归位。本文综合了保幅偏移、角度道集提取以及AVO反演等前人的工作,提出直接从炮集数据反演AVO属性的方法,以期显著减少上述三个因素对AVO反演精度的影响。 相似文献
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13.
针对传统Kirchhoff叠前时间偏移方法的一些不足,以及振幅随入射角、方位角变化(AVA/AVAZ)分析的需要,本文提出一种基于射线理论的三维叠前时间偏移角度域成像方法.它通过横向均匀介质中稳健的射线追踪建立单程波走时和传播角度的数值表,然后在此基础上估算反射波双程走时以及在界面处传播的方位角和入射角,最后基于脉冲响应叠加原理获得三维构造图像和方位\|角度域共成像点道集.与传统方法不同之处在于,上述过程均考虑了地震波在垂向变速介质中的射线弯曲效应和三维传播特征,有利于准确提取随入射角和方位角变化的振幅和时差信息.理论模型合成数据和实际地震资料测试结果展示了方法的优越性与实用性. 相似文献
14.
逆时偏移在提高复杂介质的成像质量方面表现出了优越的性能,但逆时偏移对速度精度的要求比较高.共成像点道集是一种非常重要的叠前深度偏移输出,它除了能为深度偏移处理提供速度信息外,还能够提供振幅和相位等信息,为后续的属性解释提供依据.本文提出一种在逆时偏移成像过程中提取角度域共成像点道集的方法,该方法采用矢量波动方程进行波场传播,并用能流密度矢量(Poynting vector)计算反射角,最后应用互相关成像条件输出角度域共成像点道集.该方法简单易于实现,且几乎不需要额外的计算量和存储量,非常适合于进行逆时偏移速度分析,同时提出的角道集也能用于进行AVA等分析.最后通过模型算例和实际数据检验了方法的有效性和优越性. 相似文献
15.
16.
2D multiscale non-linear velocity inversion 总被引：2，自引：0，他引：2
An efficient and robust non-linear inversion method for velocity optimization combining a global random search followed by a simplex technique is presented. The background velocity field is estimated at different spatial scales by analysing image gathers after iterative prestack depth migrations. First, the global random search is used to determine the main features/trends of the velocity model (large-scale component). Then, the simplex technique improves the resolution of the velocity field by estimating smaller-scale features. A measure of the quality of the velocity model (objective function) is based on flattening offset events in depth-migrated image gathers. To help constrain the solution, the algorithm can incorporate a priori information about the model and a smoothness condition. This 2D velocity estimation offers the benefit of being semi-automatic (requiring minimal human intervention) as well as providing a global and objective solution (which is a useful approach to an interpretation-derived velocity-estimation technique). The method is applied to a real data set where AVO analysis is carried out after prestack depth migration, as structural effects are non-negligible. It is demonstrated that the method can successfully estimate a laterally inhomogeneous velocity model at a computational cost modest compared with an interpretation-based iterative prestack depth velocity-analysis technique. 相似文献
17.
The hazards of amplitude versus offset (AVO) technique mostly applied in seismic explorations for predicting coalbed methane (CBM) content mainly derive from multi-stage amplitude modifications during seismic signal preprocessing. The modifications are undoubtedly necessitated by improving high signal-to-noise ratio (SNR) and high resolution, and achieve high fidelity to some extent; and nevertheless lead to an unfavorable possibility to implement CBM AVO analysis. Similar to sandstone reservoir with gas, AVO analysis preprocessing for CBM reservoir strictly abides by a relative amplitude preserved (RAP) principle and particularly emphasizes on preserving the evanescent class IV AVO anomaly. As for those indispensable dealings with linear noise attenuations, near-surface variety compensations and time/depth spatial imaging, the key technologies adapted to CBM AVO preprocessing should use radial trace (RT) filter, refined surface-consistent amplitude compensation (SCAC), and RAP Kirchhoff prestack time migration (PSTM). The theoretical analysis and one real 3D example in this paper demonstrate that three key technologies compliant to RAP principle in CBM AVO preprocessing can preserve the class IV AVO anomaly and benefit an operation of CBM AVO analysis and an improvement of CBM evaluation. 相似文献
18.
基于波场延拓的叠前深度偏移是实现复杂构造地质体成像的最可靠方法,但存在着计算量大、对观测系统适应性差等缺点.面炮偏移是波动方程实现精确叠前成像的另一类方法,具有较高的计算效率,不存在偏移孔径问题,而且可以通过控制照明方法,解决平面波在目标区域的能量补偿问题.本文采用面炮成像技术进行叠前深度偏移,通过对面炮震源下行波场的质量控制和优选射线个数和范围,以达到最佳的成像效果.采用控制照明技术,较大地提高了目标地层的成像精度.与此同时,得到振幅随入射角变化(AVA)道集,有利于叠前振幅解释和储层岩性预测.数据实验表明面炮成像技术是一种快速有效的方法,其成像精度与单平方根算子的共炮点道集偏移和双平方根算子的共中心点道集偏移相当,但在计算速度上要快得多,而且易于并行计算. 相似文献
19.
Jia-Jia Yang Xi-Wu Luan Bing-Shou He Gang Fang Jun Pan Wei-Min Ran Tao Jiang 《应用地球物理》2017,14(4):492-504
Angle-domain common-image gathers (ADCIGs) transformed from the shotdomain common-offset gathers are input to migration velocity analysis (MVA) and prestack inversion. ADCIGs are non-illusion prestack inversion gathers, and thus, accurate. We studied the extraction of elastic-wave ADCIGs based on amplitude-preserving elastic-wave reversetime migration for calculating the incidence angle of P-and S-waves at each image point and for different source locations. The P-and S-waves share the same incident angle, namely the incident angle of the source P-waves. The angle of incidence of the source P-wavefield was the difference between the source P-wave propagation angle and the reflector dips. The propagation angle of the source P-waves was obtained from the polarization vector of the decomposed P-waves. The reflectors’ normal direction angle was obtained using the complex wavenumber of the stacked reverse-time migration (RTM) images. The ADCIGs of P-and S-waves were obtained by rearranging the common-shot migration gathers based on the incident angle. We used a horizontally layered model, the graben medium model, and part of the Marmousi-II elastic model and field data to test the proposed algorithm. The results suggested that the proposed method can efficiently extract the P-and S-wave ADCIGs of the elastic-wave reverse-time migration, the P-and S-wave incident angle, and the angle-gather amplitude fidelity, and improve the MVA and prestack inversion. 相似文献
20.
地震波传播算子的计算效率和精度是制约三维叠前深度偏移的关键因素. 广义屏传播算子(GSP, Generalized Screen Propagator)是一种在双域中实现的广角单程波传播算子. 这一方法略去了在非均匀体之间发生的交混回响,但它可以正确处理包括聚焦、衍射、折射和干涉在内的各种多次前向散射现象. 通过背景速度下的相移和扰动速度下的陡倾角校正,广义屏算子能够适应地层速度的强烈横向变化. 这种算子可以直接应用于炮集叠前偏移,通过将广义屏算子作用于双平方根方程,还可以获得一种高效率、高精度的炮检距域叠前深度偏移方法,用于二维共炮检距道集和三维共方位角道集的深度域成像. 本文首先简述了炮检距域广义屏传播算子的理论,进而讨论了共照射角成像(CAI, Common Angle Imaging)条件,由此给出各个不同照射角(炮检距射线参数)下的成像结果,进而得到共照射角像集. 由于照射角和炮检距的对应关系,共照射角像集又为偏移速度分析和AVO(振幅随炮检距变化)分析等提供了有力工具. 相似文献