地质雷达有限差分逆时偏移方法研究

地质雷达技术是用于研究水文、环境与气候变化等重大科学问题最有效的地球物理技术之一,并广泛应用于检测道路和建筑内部结构,探测冻土层、沙漠沙丘演化特征,进行地质灾害和考古探测等.具有探测速度快、分辨率高和探测结果直观成像的优势.但由于受到介质横向速度变化,孤立块体的绕射波和倾斜界面复杂反射波的影响等,在雷达探测剖面上经常难以真实地反映地下目标体的空间位置和形态.偏移处理技术可以提高成像的真实性.逆时偏移能有效地利用回转波、多次波成像,使反射波准确归位,绕射波完全收敛,是一种受横向变化影响小,倾斜界面成像精度高的偏移方法.本文推导出基于麦克斯韦方程组TM波方程的有限差分格式、稳定性条件和PML边界条件,并编程实现有限差分零偏移距逆时偏移算法.两层模型和空洞模型的逆时偏移剖面与对应的原速度模型完全相同,有效地验证了有限差分零偏移距逆时偏移算法的准确性.相比于两层模型和空洞模型的Kirchhoff偏移剖面,逆时偏移剖面能更有效地提高垂直界面和空洞底界面的成像分辨率,更真实地反映两层模型和空洞模型的空间形态和内部结构信息.     

关于共反射面元叠加方法在实际应用中的一些思考

共反射面元（Common Reflection Surface=CRS）叠加是一种特殊的零偏移距成像方法,实践中它具有独立于宏观速度模型和完全数据驱动实现的鲜明特色,CRS叠加理论认为在得到高质量的零偏移距剖面的同时,还可以得到三个有用的波场属性参数剖面反演宏观速度模型,CRS叠加剖面之后的叠后深度偏移质量将超过叠前深度偏移.虽然CRS叠加倡导的成像方式和承诺的上述理想境界带来了全新的启示,但是实践中这些特色同样带来了令人困扰的问题,为此我们提出了倾角分解CRS叠加方法解决这些问题.本文即是作者通过上述实践之后对CRS叠加方法形成的一些思考和总结.     

CGP叠加柱面波偏移成像方法

针对松辽盆地薄砂层油藏的地震勘探问题,提出了一种共检波器接收点(CGP)叠加柱面波偏移成像方法。该方法对小炮点距、小检波器点距、中间放炮观测系统采集地震资料,经CGP道集叠加组合成柱面波剖面;采用下行波射线法向下延拓和上行波波动方程向下延拓的方法,使柱面波剖面偏移成像。通过模型分析和对松辽盆地TK8157测线资料进行处理证明该方法的地震分辨率和保真度较高,在发现小砂体、小断层、地层尖灭等方面有较好的效果。     

多波高斯束叠前深度偏移速度分析(英文)

多分量地震资料叠前深度偏移技术可以对地下复杂地质构造进行更准确的成像,精确成像的前提是获取准确的纵横波偏移速度。本文采用高斯束偏移方法对多波地震数据进行偏移速度分析,首先分别给出纵波和转换波共偏移距域高斯束叠前深度偏移方法原理,在此基础上抽取纵波和转换波偏移距域共成像点道集;然后根据共成像点道集拉平准则,分别对纵波和横波速度进行更新;当两种波成像深度不一致时,对纵波和转换波成像剖面进行深度匹配,完成高精度的纵横波偏移速度分析。模型数据和实际资料试算表明,该方法是一种有效的多波偏移速度分析方法。     

深反射地震资料的偏移处理

本文在对偏移理论和相关算法进行概括性的梳理和总结之外,主要针对深反射地震资料叠前偏移方法进行介绍,对初始数据的规则化、偏移孔径、去假频因子以及速度模型等关键参数进行详细的测试和深入地探讨.适当的规则化处理能提高深反射地震资料中反射信号的连续性和剖面整体能量的均一性;合理的偏移孔径能让波场能量很好地收敛、陡倾角反射层能够准确归位以及岩石圈中、深部的精细结构能较好地成像,同时又不至于引入严重的偏移噪音;通过选择适当的去假频因子来减少剖面上的高频干扰,使得整个剖面的高、低频能量分布适中;精确的速度模型是影响偏移结果的关键性因素,通过对速度模型的不断迭代优化,能显著地提高深反射地震剖面的中、深部偏移成像的精度和准确性,为后续深反射地震资料的综合解释打下良好基础.     

叠前地震数据的平面波深度偏移法

提出了一套基于平面波分解的波动方程叠前地震数据深度偏移方法. 通过对共炮点道集和共偏移距道集地震数据的平面波分解，分别得到适用于单平方根波场外推方程和双平方根波场外推方程的共ps（炮点坐标平面波参数）平面波道集和共ph（偏移距坐标平面波参数）平面波道集. 在对共炮点道集和共偏移距道集地震数据的平面波分解时，不需要进行通常意义下的τ p变换计算. 通过对共ps平面波道集和共ph平面波道集的偏移效果对比，我们认为在速度弱横向变化介质中，两种平面波道集偏移方法的效果相当，但对于速度强横向变化介质，共ps平面波道集偏移方法的效果要优于共ph平面波道集偏移方法. 在计算效率方面，共ps平面波道集偏移方法与共ph平面波道集偏移方法基本相同.     

输出道方式的共反射面元叠加方法Ⅱ--实践

CRS MZO方法是一种以输出道成像方式合成零偏移距剖面的共反射面元（Common Reflection Surface）叠加算法,它以完全不同的方式实现了CRS叠加.理论I已经对CRS MZO叠加方法的理论进行了详细介绍,本文进一步将CRS MZO方法用于对实际资料的处理.处理结果表明CRS MZO方法有效地改善了零偏移距剖面的成像质量,体现了CRS叠加理论的特点.在结合倾角分解策略消除了倾角歧视现象后,倾角分解CRS MZO方法完全能够用于处理实际数据,为得到高质量的零偏移距剖面提供了一个新的手段.     

柴达木盆地三湖地区天然气地震预测关键技术及应用

针对柴迭木盆地三湖生物天然气预测,提出了地震预测方法的三项关键技术:地震资料处理中的静校正技术(初至波折射静校正技术);地震叠后预测技术(包括如下5项内容:共偏移距扫描;频率扫描;速度谱剖面分析;反射同相轴下拉量分析;烃类检测);地震叠前预测技术(包括如下2项内容:不同偏移距叠加剖面分析;叠前反演分析).在三湖北斜坡地区应用这三项关键技术,发现了台东2号舍气异常,成功钻探了台东2井.     

Kirchhoff偏移法在探地雷达正演图像处理中的应用

本文首先通过对波动方程的分析,得出了声波波动方程和雷达波波动方程形式一致性,从而说明了把广泛应用在地震数据处理中的偏移技术引入到GPR资料处理中的可行性;其后说明了时域有限差分法（FDTD）的原理,并用它合成了几种常见的雷达正演剖面;最后利用Kirchhoff积分偏移法对正演所得的雷达剖面进行偏移处理,通过对比偏移处理前后的雷达正演剖面,可知Kirchhoff积分偏移法能使雷达正演剖面中的反射波的归位,绕射波收敛,从而大大地提高了雷达正演剖面的分辨率,更好地指导GPR剖面的地质解释和验证偏移方法的有效性.     

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.     

Imaging of offset VSP data acquired in complex areas with modified reverse-time migration

A modified reverse-time migration algorithm for offset vertical seismic profiling data is proposed. This algorithm performs depth imaging of target areas in the borehole vicinity without taking into account the overburden. Originally recorded seismograms are used; reliable results can be obtained using only the velocity profile obtained along the well. The downgoing wavefield emitted from a surface source is approximated in the target area using the transmitted P-wave, recorded by the receivers deployed in the well. This is achieved through a reverse-time extrapolation of the direct transmitted P-wave into the target area after its separation in offset vertical seismic profiling seismograms generated using a finite-difference scheme for the solution of the scalar wave equation.
The proposed approach produces 'kinematically' reliable images from reflected PP- and PS-waves and, furthermore, can be applied as a salt proximity tool for salt body flank imaging based on the transmitted PS-waves. Our experiments on synthetic data demonstrate that the modified reverse-time migration provides reliable depth images based on offset vertical seismic profiling data even if only the velocity profile obtained along the borehole is used.     

Near-surface velocity model construction based on a Monte-Carlo scheme

In tomographic statics seismic data processing, it is crucial to determine an optimum base for a near-surface model. In this paper, we consider near-surface model base determination as a global optimum problem. Given information from uphole shooting and the first-arrival times from a surface seismic survey, we present a near-surface velocity model construction method based on a Monte-Carlo sampling scheme using a layered equivalent medium assumption. Compared with traditional least-squares first-arrival tomography, this scheme can delineate a clearer, weathering-layer base, resulting in a better implementation of datuming correction. Examples using synthetic and field data are used to demonstrate the effectiveness of the proposed scheme.     

基于实例分析的绿色钢结构抗震与环保性能研究

为优化绿色钢结构建筑的安全性能与环保性能,基于一40层框架-支撑钢结构建筑实例进行抗震性能与环保性能分析。根据实际建筑参数构建该绿色钢结构建筑剖面图,基于时程分析法记录不同地震波作用下建筑水平位移随时间变化情况,基于Pushover分析法分析方钢管混凝土组合异形柱在罕见地震中的基底剪力和弹塑性变形,基于对比实验方法验证其环保优越性,并得出以下结论：建筑的方钢管混凝土组合异形柱符合国家抗震性能要求,整体建筑的抗震性能随楼层的增加而减弱;与钢筋混凝土结构、砖混结构相比,钢结构能有效节约施工水电用量、降低施工噪声,是一种抗震性强、环保性能优的绿色建筑形式。     

In situ experiments and seismic analysis of existing buildings. Part II: Seismic integrity threshold

The interest of in situ measurements (presented in Part I paper) for a seismic assessment of existing buildings is analysed in this paper. It is shown that the experimental modal characteristics obtained on regular concrete structures are described successfully by suited Timoshenko beam modelling. For a given structure, taking into account the experimental data, the corresponding beam model, and choosing the maximum tensile strain of concrete as damage criterion for key structural elements, a maximum level of the ground acceleration can be determined. This so‐called seismic integrity threshold is directly related to the onset of structural damages. This new approach is illustrated on one of the studied buildings. The advantages of using ambient vibrations survey for the vulnerability assessment of existing buildings are discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

LARGE-OFFSET APPROXIMATIONS IN THE MODIFIED CAGNIARD METHOD FOR COMPUTING SYNTHETIC SEISMOGRAMS: A SURVEY1

Large horizontal offset and large vertical offset approximations in the modified Cagniard method for computing synthetic seismograms in a horizontally layered model of the earth are derived. They apply to each of the generalized-ray constituents into which the seismic wave motion is decomposed. For the results applying to large horizontal offset, which are known in the seismological literature, a simplified derivation is given. The results for large vertical offset, which are of particular interest to vertical seismic profiling, are new. The use of the large-offset approximations, both horizontal and vertical, leads to a considerable reduction in computation time for synthetic seismograms compared with the full three-dimensional version of the modified Cagniard method.     

Seismic attenuation in Faroe Islands basalts

We analysed vertical seismic profiling (VSP) data from two boreholes at Glyvursnes and Vestmanna on the island of Streymoy, Faroe Islands, to determine the magnitude and causes of seismic attenuation in sequences of basalt flows. The work is part of SeiFaBa, a major project integrating data from vertical and offset VSP, surface seismic surveys, core samples and wireline log data from the two boreholes. Values of effective seismic quality factor (Q) obtained at Glyvursnes and Vestmanna are sufficiently low to significantly degrade the quality of a surface reflection seismic image. This observation is consistent with results from other VSP experiments in the North Atlantic region. We demonstrate that the most likely cause of the low values of effective Q at Glyvursnes and Vestmanna is a combination of 1D scattering and intrinsic attenuation due to seismic wave‐induced fluid flow within pores and micro‐cracks. Tests involving 3D elastic wave numerical modelling with a hypothetical basalt model based on field observations, indicate that little scattering attenuation is caused by lateral variations in basalt structure.     

基于多射线联合反演的速度无关叠前地震数据Q值估计

描述地震波衰减特征的品质因子Q对地震数据处理和油藏描述非常重要,在地震勘探领域,Q值一般通过垂直地震剖面(VSP)数据或地面地震数据得到.由于叠前地面地震数据具有复杂的射线路径且存在噪声、调谐干涉效应等影响,从叠前地震数据中准确估计Q值相对困难.本文以地震波射线传播为基础,根据同相轴局部斜率和射线参数的映射关系,将多射线波形频谱同时带入谱比法联合反演估计Q值,提出了基于多射线联合反演的速度无关叠前Q值估计方法.该方法通过局部斜率属性避开了速度对Q值估计的影响,局部斜率携带地震波传播的速度信息,具有相同局部斜率的地震反射波具有相同的传播射线参数.同相轴局部斜率是地震数据域的属性,而速度是模型域的参数,在估计Q值中采用数据域的属性参数可以直接应用于数据的联合反演,而不需要通过速度对其做进一步的转化,从而提高了Q值估计的精度.同时,本方法采用预测映射(predictive mapping)技术将非零炮检距反射信息映射到零炮检距处,从而获得零偏移距走时对应的Q值.模拟和实际算例验证了本文方法的有效性.     

Dreamlet source‐receiver survey sinking prestack depth migration

Survey sinking migration downward continues the entire surface observed multi‐shot data to the subsurface step by step recursively. Reflected energy from reflectors at current depth appear at zero time and zero offset in the extrapolated wavefield. The data (seismic records) of t > 0 at this depth are equivalent to the data acquired by a survey system deployed at this depth. This is the reason to name the process ‘survey sinking’. The records of negative time need not to be further propagated since they carry no information to image structures beneath the new survey system. In this paper, we combine survey sinking with dreamlet migration. The dreamlet migration method decomposes the seismic wavefield and one‐way wave propagator by complete time‐space localized bases. The localization on time gives flexibility on time‐varying operations during depth extrapolation. In dreamlet survey sinking migration, it only keeps the data for imaging the structures beneath the sunk survey system and gets rid of the data already used to image structures above it. The deeper the depth is, the shorter is the valid time records of the remaining data and less computation is needed for one depth step continuation. For data decomposition, in addition to time axis, dreamlet survey sinking also decomposes the data for source and receiver gathers, which is a fully localized decomposition of prestack seismic data. A three‐scatter model is first used to demonstrate the computational feature and principle of this method. Tests on the two‐dimensional SEG/EAGE salt model show that with reduced data sets the proposed method can still obtain good imaging quality on complex geology structures and a strong velocity contrast environment.     

菲涅耳体地震层析成像分辨率研究

层析成像分辨率的研究,不仅可以帮助分析层析方法的反演能力,评价层析反演的效果,还可以帮助指导层析参数设置,优化观测系统设计等.本文对比研究了前人提出的两种菲涅耳体层析成像分辨率的计算方法,并针对其存在的问题进行了优化.文中通过对二维理论模型的定量计算,总结了菲涅耳体地震层析成像分辨率的一些规律,并将其与射线层析的分辨率...     

Seismic cracking and energy dissipation in concrete gravity dams

A finite element method for seismic fracture analysis of concrete gravity dams is presented. The proposed smeared crack analysis model is based on the non-linear fracture behaviour of concrete. The following features have been considered in the development of the model: (i) the strain softening of concrete due to microcracking; (ii) the rotation of the fracture band with the progressive evolution of microcrack damage in finite elements; (iii) the conservation of fracture energy; (iv) the strain-rate sensitivity of concrete fracture parameters; (v) the softening initiation criterion under biaxial loading conditions; (vi) the closing-reopening of cracks under cyclic loading conditions. The seismic fracture and energy response of dams and the significance of viscous damping models to take account of non-cracking structural energy dissipation mechanisms are discussed. The influences of global or local degradation of the material fracture resistance on the seismic cracking response of concrete dams were also studied. Two-dimensional seismic response analyses of Koyna Dam were performed to demonstrate the application of the proposed non-linear fracture mechanics model.