Anisotropic converted wave amplitude-preserving prestack time migration by the pseudo-offset method

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.

Amplitude.preserving plane-wave prestack time migration for AVO analysis

To support amplitude variation with offset （AVO） analysis in complex structure areas, we introduce an amplitude-preserving plane-wave prestack time migration approach based on the double-square-root wave equation in media with little lateral velocity variation. In its implementation, a data mapping algorithm is used to obtain offset-plane-wave data sets from the common-midpoint gathers followed by a non-recursive phase-shift solution with amplitude correction to generate common-image gathers in offset-ray-parameter domain and a structural image. Theoretical model tests and a real data example show that our prestack time migration approach is helpful for AVO analysis in complex geological environments.

Fast least-squares prestack time migration via accelerating the explicit calculation of Hessian matrix with dip-angle Fresnel zone

Amplitude versus offset analysis is a fundamental tool for determining the physical properties of reservoirs but generally hampered by the blurred common image gathers(CIGs).The blurring can be optimally corrected using the blockwise least-squares prestack time migration(BLS-PSTM),where common-offset migrated sections are divided into a series of blocks related to the explicit offsetdependent Hessian matrix and the following inverse filtering is iteratively applied to invert the corresponding reflectivity.However,calculating the Hessian matrix is slow.We present a fast BLS-PSTM via accelerating Hessian calculation with dip-angle Fresnel zone(DFZ).DFZ is closely related to optimal migration aperture,which significantly attenuates migration swings and reduces the computational cost of PSTM.Specifically,our fast BLS-PSTM is implemented as a two-stage process.First,we limit the aperture for any imaging point with an approximated the projected Fresnel zone before calculating the Hessian matrix.Then,we determine whether a seismic trace contributes to the imaging point via DFZ during calculating the Hessian matrix.Numerical tests on synthetic and field data validate the distinct speedup with higher-quality CIGs compared to BLS-PSTM.

Traveltime tomography and prestack depth migration for vertical seismic profiling of an angle-domain walkaway on a complex surface

Walkaway VSP cannot obtain accurate velocity field,as it asymmetrically reflects ray path and provides uneven coverage to underground target,thereby presenting issues related to imaging quality.In this study,we propose combining traveltime tomography and prestack depth migration for VSP of an angle-domain walkaway,in a bid to establish accurate two-dimensional and three-dimensional(3 D)velocity models.First,residual curvature was defined to update velocity,and an accurate velocity field was established.To establish a high-precision velocity model,we deduced the relationship between the residual depth and traveltime of common imaging gathers(CIGs)in walkaway VSP.Solving renewal velocity using the least squares method,a four-parameter tomographic inversion equation was derived comprising formation dip angle,incidence angle,residual depth,and sensitivity matrix.In the angle domain,the reflected wave was divided into up-and down-transmitted waves and their traveltimes were calculated.The systematic cumulative method was employed in prestack depth migration of a complex surface.Through prestack depth migration,the offset-domain CIGs were obtained,and dip angle was established by defining the stack section horizon.Runge–Kutta ray tracing was employed to calculate the ray path from the reflection point to the detection point,to determine the incident angle,and to subsequently calculate the ray path from the reflection point to the irregular surface.The offset-domain residual depths were mapped to the angle domain,and a new tomographic equation was established and solved.Application in the double complex area of the Tarim Basin showed the four-parameter tomographic inversion equation derived in this paper to be both correct and practical and that the migration algorithm was able to adapt to the complex surface.

Internal Multiple Prediction Based on Imaging Profile Prediction and Kirchhoff Demigration

This paper introduces an internal multiple prediction method based on imaging profile prediction and Kirchhoff demigration.First,based on an inputted prestack time migration profile,the method predicts the prestack time migration profile that only includes internal multiples by inverse scattering series method.Second,the method uses velocity-weighted Kirchhoff demigration to create shot gathers that contains only internal multiples.Internal multiple prediction based on the prestack time migration profile effectively reduces the computational cost of multiple predictions,and the internal-multiple shot gathers created by Kirchhoff demigration remarkably reduces the complexity of the practical problem.Internal multiple elimination can be conducted through the combined adaptive multiple subtraction based on event tracing.Synthetic and field data tests show that the method effectively predicts internal multiples and possesses considerable potential in field data processing,particularly in areas where internal multiples develop seriously.

Reverse-Time Prestack Depth Migration of GPR Data from Topography for Amplitude Reconstruction in Complex Environments

With increased computational power, reverse-time prestack depth migration（RT-PSDM） has become a preferred imaging tool in seismic exploration, yet its use has remained relatively limited in ground-penetrating radar（GPR） applications. Complex topography alters the wavefield kinematics making for a challenging imaging problem. Model simulations show that topographic variation can substantially distort reflection amplitudes due to irregular wavefield spreading, attenuation anomalies due to irregular path lengths, and focusing and defocusing effects at the surface. The effects are magnified when the topographic variations are on the same order as the depth of investigation––a situation that is often encountered in GPR investigations. Here, I use a full wave-equation RT-PSDM algorithm to image GPR data in the presence of large topographic variability relative to the depth of investigation. The source and receiver wavefields are propagated directly from the topographic surface and this approach inherently corrects for irregular kinematics, spreading and attenuation. The results show that when GPR data are acquired in areas of extreme topography, RT-PSDM can accurately reconstruct reflector geometry as well as reflection amplitude.

库车坳陷复杂高陡构造地震成像研究

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.

山地地震资料叠前时间偏移方法及其GPU实现

山地地区地下地质结构复杂,地表高差大,变化剧烈.目前该类地区地震勘探中主要的成像手段依然是Kirchhoff叠前时间偏移.但地表高程的剧烈变化使叠前时间偏移的基准面很难选择.本文在传统方法的基础上,提出了一种在浮动基准面上修正常规叠前时间偏移走时计算的叠前时间偏移方法,该方法能够很大程度上提高山地地区、特别是地表高差变化大地区的成像效果.本文还介绍了GPU在叠前时间偏移上的应用,通过GPU对叠前时间偏移的优化和实现,得出如下结论:应用单颗NVIDIA Tesla C1060 GPU进行叠前时间偏移,相比应用主频2.5 GHz的单核CPU计算效率可提高70倍以上.

各向异性叠前偏移技术及应用

以塔里木盆地碳酸盐岩实际地震资料为例,论述了各向异性叠前偏移技术、各向异性参数的求取方法以及各向异性偏移的处理流程。应用效果证实,相对保幅的各向异性叠前偏移技术,通过求取更为准确的各向异性速度和保留丰富的远偏移距振幅信息,提高了偏移速度和偏移算子的精度,有效提高了塔里木盆地碳酸盐岩地震成像品质,使"串珠"反射特征更清楚,断层和断点刻画更加清晰,从而提高地震储集层描述的精度。

多方位AVO技术在裂缝检测中的应用

在共反射点三维道集的地震资料中,振幅不仅随入射角变化而变化,而且也随方位角变化而变化。振幅随方位角的变化与地层的各向异性具有一定的对应关系,尤其当地层出现一定方位的裂缝时,近平行裂缝和近垂直裂缝方向上共反射点道集的AVO属性参数会表现出明显的差异,这种差异的大小和平面展布正好反映了裂缝的发育程度和分布。本文在对三维纵波道集资料进行叠前时间偏移的基础上,分别抽取沿主测线和联络测线两个方向的道集资料进行AVO异常属性参数分析,然后对比分析两个方向的属性参数的差异,最后应用差异的大小和分布检测了裂缝的发育状况。结果表明,这种方法预测的裂缝与钻井取心和成像测井反映的裂缝发育状况有较好吻合性,与相干体所指示的断裂分布也有一定的关系。

三维地震资料叠前时间偏移应用研究

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.

2D共炮时间域高斯波束偏移

针对传统射线方法在奇异区成像精度不高,而2D频率域高斯波束叠前深度偏移需要计算成像点处每个频率的格林函数,影响计算效率的问题,本文通过使用复走时代替实走时,改变频率域下成像公式的积分顺序,给出了在时间域下进行高斯波束偏移的方法和计算公式.本文使用复杂数值模型验证了2D时间域高斯波束叠前偏移方法的正确性,并同传统射线偏移成像结果做了对比.对比结果表明时间域高斯波束偏移在成像精度上优于传统射线偏移.

克希霍夫叠前时间偏移技术在复杂构造带地震资料处理中的应用

在辽河盆地东部凹陷中部的A区块地下构造复杂,以往的资料虽然反应了该区的整体面貌,但断裂带的成像效果不是很好,为此,开展了叠前时间偏移处理技术研究.详细介绍了保福克希霍夫叠前时间偏移的原理和数据的预处理,讨论了主要的偏移参数的测试和选取方法,通过Deregowski循环法和百分比偏移扫描速度建立和优化速度模型.处理结果表明,该区三维叠前偏移剖面较常规三维叠后偏移剖面有明显改善.

谱元法叠前逆时偏移研究

谱元法是基于弹性力学方程的弱形式,运用有限元的思想在单元上进行谱展开,理论上该方法具备有限元适应任意复杂介质模型的韧性和伪谱法的精度.这里借助谱元法这一思想,在正演算法的基础上,进行偏移算法的改编,并在各向异性介质的二个模型中进行叠前逆时偏移.结果表明:这二个模型上进行的偏移结果与模型吻合较好.

基于叠前时间偏移资料的AVO处理技术

与国外的处理流程相比,国内AVO资料处理过程中一般不作归位处理,这使AVO资料在应用上受到一定限制。针对这一问题,在胜利油田永安地区的AVO资料处理过程中,使用克希霍夫叠前时间偏移技术对常规CMP道集进行归位,得到了CRP道集。在此基础上进行AVO分析,不但较好地解决了AVO异常的归位问题,而且叠前时间偏移使绕射能量归位,削弱了随机噪音的干扰,使AVO响应更清晰,提高了AVO资料的分析质量。介绍了AVO资料处理过程中叠前时间偏移的实现步骤,包括数据准备、偏移速度场的建立、偏移实现过程和偏移后CRP道集处理等,并结合实际资料进行了效果分析。

起伏地表叠前时间偏移处理流程及其应用研究

复杂山地地表高程变化剧烈,影响速度分析和速度建模,造成偏移归位不准确。为消除山地地震资料偏移处理因高程变化大引起成像聚焦变差的问题,有效避开低信噪比下的深度域速度建模,提出了一套基于起伏地表叠前时间偏移的处理流程,主要处理步骤包括成像基准面构建、基于成像基准面的速度模型更新和起伏地表叠前时间偏移。构建成像基准面的目的是使获得的速度模型与实际速度模型最大程度相吻合;基于成像基准面的速度模型更新能使速度模型更有效地收敛;还原实际炮、检点关系的起伏地表叠前时间偏移提高了时间偏移的聚焦能力。西部某山区实际资料的处理结果表明,采用该处理流程得到的剖面品质高、分辨率显著提升、断点清晰、断面刻画明显,为后续解释工作提供了很好的资料。

断陷盆地大面积三维叠前时间偏移连片处理的地质意义及关键技术

中国东部陆相断陷盆地含油气构造带已经基本完成了三维地震勘探工作。为了能够按现代层序地层学理 论重新认识和评价这些断陷盆地,开展断陷盆地大面积三维叠前时间偏移是一项必然的选择。本文以南堡凹陷 为例,重点对叠前时间偏移连片处理的可行性及关键技术进行了分析。通过南堡凹陷取得的处理效果表明,在 陆相断陷盆地实施大面积三维地震资料叠前时间偏移连片处理,对于深化地质认识、挖掘老区潜力、突破新区 勘探、实现油田的可持续发展具有重要意义。

一种补偿介质吸收叠前时间偏移技术

通过引入描述黏性吸收的等效Q值参数,发展了补偿介质吸收的叠前时间偏移方法。该方法基于地表观测数据建立等效Q值模型,应用补偿因子的光滑性阈值控制解决介质黏性吸收补偿的稳定性问题。基于倾角域菲涅尔带估计,结合稳相偏移的补偿介质吸收叠前时间偏移技术能够在压制介质吸收补偿噪声的同时提高计算效率。利用多流、双缓存机制实现补偿介质吸收叠前时间偏移的GPU/CPU协同计算,缩短了计算时间。大庆油田实际地震数据的应用结果表明,该技术可恢复地震波中被衰减的高频成分,提高地震成像的分辨率,其成果数据支持了大庆油田扶余油层致密油的水平井勘探部署。

几种叠前深度偏移技术效果的对比

在回顾叠前深度偏移发展历程的基础上,概述了当前几类叠前深度偏移方法:克希霍夫积分法、波动方程法、逆时偏移。在分析叠前深度偏移的波场成像方法、适用性、近地表条件敏感性及存在问题的基础上,对比偏移剖面,比较不同偏移方法的成像效果,指出叠前深度偏移的发展方向,为以后的叠前深度偏移的研究提供参考建议。

DMO和叠前时间偏移的共同起点

王华忠 ,徐蔚亚 ,徐兆涛 ,匡斌 ,马在田 .DMO和叠前时间偏移的共同起点 .石油地球物理勘探 ,2 0 0 2 ,37(3) :2 2 4～ 2 2 9DMO和叠前时间偏移对于改善速度分析及叠加效果 ,最终提高剖面成像质量都是很有用的工具 ,一般在共偏移距道集中进行。其实现方法有多种 ,如等价偏移距方法 (equivalent offset migration,Bancroft et al,1994 )、DMO+PSI(prestack imaging)方法 (Gardner,1986 )和非成像的炮集偏移 (non- imaging shot- record m i-gration,Berryhill,1996 )等。这些方法的一个共同特点是用一个新定义的偏移距替代原来的偏移距。在每一种方法中 ,成像过程都归结为以新偏移距定义的共反射点双曲线型时—距关系上的动校正。本文中 ,我们证明了不同方法的 DMO和叠前时间偏移有其共同起点——双平方根算子 ,说明它们在原理上是等价的 ;最后我们提出了基于波动方程的 DMO和叠前时间偏移方法。