利用斯通利波速度反演地层横波速度的方法与应用研究

从严格的Ｂｉｏｔ－Ｒｏｓｅｎｂａｕｍ模型出发，在低频近似下得到井孔中斯通利波相速度的解析表达式。它与Ｔａｎｇ等从简化的Ｂｉｏｔ－Ｒｏｓｅｎｂａｕｍ模型所得到的结果类似。从理论上说明了在低频近似下简化模型的合理性，在不同频率下，对其结果中所含的声系大小修正和Ｎｏｒｒｉｓ修正作了比较。     

转换波叠前横波速度反演

摘要 地震波速度对地震资料偏移成像、岩性和岩相解释以及储层预测,均起着非常重要的作用. 在储层预测中,需要获得横波层速度信息,以减少仅用纵波速度在区分岩性和孔隙中流体类型以及含气饱和度方面的不确定性. 基于Zoeppritz方程组,提出了数值求解和速度扫描方法,对叠前转换波资料求取横波层速度. 理论模型和实际转换波资料的反演结果, 均表明该方法的效果较好.      

基于约束条件横波速度反演和流体替代

依据辽东湾地区一组在地层条件和不同流体相态下（气饱和与水饱和）实验室测定的岩石纵波速度、横波速度及密度等数据,讨论Gassmann方程在横波速度反演和流体替代方面的应用效果,指出岩石骨架剪切模量和体积模量估算精度是影响纵波、横波速度预测精度的关键因素之一,提出基于约束条件横波速度反演和流体替代方法,速度预测精度的改善十分明显.     

利用平面波地震记录同时反演层状介质纵、横波速度

提出一种利用纵波激发、纵波和横波同时接收的单个入射角平面波地震记录同时反演层状介质纵波速度和横波速度的层剥离方法.文中给出了有限带宽反演算法,对有限带宽记录及含有噪声的数据进行了试算,获得了比前人的研究有明显进展的效果.     

利用测井数据实现横波速度的反演及应用效果分析

在地震数据的AVO(Amplitude Versus Offset)反演以及储层预测分析等中都需要横波速度信息,然而目前多数地区横波速度测井资料十分匮乏,在AVO反演中,往往凭经验公式获得,其精度很低.为了获得准确的横波速度信息,我们利用测井资料由最小二乘法实现横波速度的反演,针对华北油区赛83井实际测井数据,利用纵波速度、密度测井数据反演计算了该区的横波速度,并与实测横波速度作了对比,结果发现反演与实测结果取得了较好的一致性;还将该方法反演的横波速度与几种不同反演方法反演结果作了对比,获得较为一致的结果,算例证明了该方法的有效性.在测井资料缺少的情况下,该方法作为AVO反演横波速度的初始速度建模及储层预测分析应该是一种较为实用的方法.     

软地层横波速度的偶极随钻测井反演

在电缆测井中,可以利用偶极声场中的弯曲波反演软地层的横波速度.然而,在随钻声波测井（LWD）中,钢制钻铤的存在使得井孔结构变得复杂,同时改变了井孔声场,弯曲波也变得难以测定.此外,弯曲波与钻铤波耦合在一起,使得地层横波速度的反演变得困难.本文计算分析了随钻声场的频散曲线和激发曲线,注意到了偶极舒尔特波在较宽频带内速度频散很弱,特别是在本文研究的软地层情况下,偶极舒尔特波速度在3至25 kHz的频率范围内几乎为一个常值,并且该值与地层横波速度存在一一对应关系.舒尔特波速度远小于其他模式波速度,与其他模式波在时域上易分离.相对于其他地层参数,舒尔特波对地层横波速度十分敏感.因此,它可以用来反演软地层的横波速度.

     

部分叠加资料纵横波速度测井约束反演

本文提出一种角度部分叠加资料同时反演纵波和横波速度的方法,以角度部分叠加资料为基础,利用地震波振幅随入射角变化与弹性参数间的数学关系,基于非线性最优化理论,通过将最小平方问题转化为大型带状矩阵的求解问题,采用逐道外推技术依次求得该角度剖面的每个点纵波和横波速度值,利用地震波速度在各向异性介质中与入射角的关系,进一步得到地震波零入射角纵、横波速度,从而可以求得纵横波速度比及泊松比,为地震资料的岩性及含油气性解释提供了丰富的参数信息,为保证反演的稳定性,降低多解性,采用测井、叠后构造层位解释结果的共同约束,并做好叠前去噪以及振幅保持处理.     

基于面波频散曲线聚类分析的近地表横波速度反演

获取准确的近地表横波速度对复杂地表条件下弹性波地震数据处理和成像非常重要.在浅层面波工程勘探中通过反演提取的频散曲线可以获得近地表横波速度结构.在多道面波频散曲线分析中, 频散关系拾取的精度直接影响速度反演结果的可靠性.本文在多道面波叠加及自动拾取频散曲线基础上, 提出了基于面波频散曲线聚类分析的近地表横波速度反演方法.该方法充分考虑了低信噪比条件下面波频散曲线的不确定性, 通过在频散曲线拾取中引入曼哈顿距离K-Means聚类算法提高频散曲线拾取的准确性.采用多道多窗口叠加技术提高了面波反演对横向速度变化的适应性, 通过聚类算法和多窗口叠加提高反演的可靠性, 聚类算法获得较准确的频散曲线更利于后续横波速度反演过程.模拟数据算例对比表明本文提出的方法比常规算法效果更好, 精度更高.将提出的方法应用于工程勘探和油气勘探的面波数据反演中, 结果也验证了该方法的有效性.

     

利用地震回以资料反演界面位置与速度分布

论述了利用地震回折波资料以界面位置与速度分布的方法，推导了地震波走时对于界面位置偏导数的计算公式。数值模拟和实测资料的计算结果表明了该方法的有效性和编制的计算程序的实用性，该方法最的特点是充分地利用了透射波资料中所含的界面位置的信息。界面位置的分辩率与界面两边的速度反差有关，速度判别越大，则分辨率越高。     

利用背景噪声成像研究合肥-金华剖面地壳速度结构及径向各向异性的东西差异

背景噪声成像能够为地壳内部结构提供地震波速的观测证据,能够增进对地壳结构与物性的认识.本文利用背景噪声成像方法对合肥-金华流动地震台阵55个台站数据进行了分析反演,获得了华北克拉通与华南块体东部构造边界附近区域的地壳S波速度与径向各向异性结构.成像结果表明,以东经118°-118.5°附近为界,西北部表现为地壳低速异常和中下地壳正的径向各向异性,东南部表现为地壳高速异常,下部地壳存在负的径向各向异性.由此,本文推测地震波速结构差异反映了地壳内部物质与温度的差异,这种差异与两个地区自中生代晚期以来经历了截然不同的岩浆活动相关.

     

Inversion of shear wave interval velocity on prestack converted wave data

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.     

云南地区地壳上地幔三维S波速度与径向各向异性结构研究

云南地区地处青藏高原东南缘, 一直是地球科学研究的热点地区.目前, 一些热点问题, 如云南地区是否存在中下地壳低速流及其空间分布, 仍有一定的争议.通过建立云南地区精细的地壳上地幔速度与各向异性结构, 可为深入认识上述问题提供重要信息.本文利用天然地震波形记录, 采用双台法提取了12~60 s周期的Rayleigh和Love波相速度频散, 并进一步反演获得了云南地区10~100 km的三维地壳上地幔SV和SH波速度及径向各向异性结构.结果表明:S波速度与径向各向异性结构在横向和垂向均存在显著变化.在20~30 km深度, 存在两个低速条带, 且条带内呈现出正径向各向异性(V_SH>V_SV)特征, 暗示了中下地壳低速物质的水平向运动.在80~100 km深度, 云南西南和东南部显示为低速异常和正径向各向异性特征, 暗示了软流圈物质的水平流动.在云南北部的丽江、攀枝花和昭通地区, 岩石圈地幔中则存在明显的负径向各向异性(V_SH<V_SV), 可能反映了地幔物质的上涌痕迹.历史强震多发生在地壳低速区域或高低速过渡带, 且地震附近的径向各向异性为负或者较弱.一些地震震源下方存在低速层, 地壳低速层可能会促进强震发生.

     

Inversion of waveforms from. Xiangtang borehole seismic array for soil dynamic property

In order to understand the site soil response of the Xiangtang borehole seismic array under real strong ground motion, reveal the site response, verify the technique of borehole exploration, and improve the precision of in-situ test and laboratory test, this paper presents a new approach, which is composed of two methods. One is the layered site seismic response method, whose layer transform matrix is always real. The other is a global-local optimization technique, which uses genetic algorithm (GA)-simplex method. An inversion of multi-component waveforms of P, SV and SH wave is carried out simultaneously. By inverting the records of three moderate and small earthquakes obtained from the Xiangtang borehole array (2# ) site, the soil dynamic characteristic parameters, including P velocity, damping ratio and frequency-dependent coefficient b, which has not been given in previous literatures, are calculated. The results show that the soil S wave velocity of the Xiangtang 2# borehole is generally greater than that obtained from the 1994 in-situ test, and is close to the velocity of the 3# borehole, which is more than 200 m away from the 2# borehole. Meanwhile, perceptible soil nonlinear behavior under peak ground motion of about 60×10-2m/s2 is detected by the inversion analysis. The presented method can be used for studying the soil response of other borehole array sites.     

On the propagation of an in-plane shear fault with super-S-wave velocity

The speedv, especially the problem whether super S-wave velocity in the classical model (linear elasticity fracture mechanics) exists, of spontaneous propagation of a shear fault is investigated theoretically. An in-plane shear crack propagating in the crack plane is taken as the model of the shear fault. The results obtained firstly by Kostrov (1975) is extended from sub-Rayleigh wave velocity to super S-wave velocity, and the analytical expression for the stress intensity factorK ₂ in the case ofα>v>β is derived. It is proved that for Poisson mediumK ₂ is positive and real in the velocity range (β, 1.70β). This demonstrates that (β, 1.70β) is the velocity range which fulfils the conditions for spontaneous crack propagation. The existence, convergence and positiveness or negativeness ofK ₂ forv in individual sections are examined, and it is found that for an in-plane shear crack: 1. There are three sections forv, i.e., [0.v _R], (β, 1.70β), andα, respectively, and 2. There are two physically reasonable sections forv, the first is [v _R, β], and the second is [1.70β, α]. These two forbidden sections behave as barriers to fault propagation. The analytical expressions derived in this paper are not only suitable to classical model, but also to the other derivative models (e. g., the slip-weakening model and the renomalization model etc.). The model considered in this paper is more realistic than the static model employed by previous authors. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica, 15, 9–14, 1993.     

Surface‐wave inversion for a P‐velocity profile with a constant depth gradient of the squared slowness

Surface waves are often used to estimate a near‐surface shear‐velocity profile. The inverse problem is solved for the locally one‐dimensional problem of a set of homogeneous horizontal elastic layers. The result is a set of shear velocities, one for each layer. To obtain a P‐wave velocity profile, the P‐guided waves should be included in the inversion scheme. As an alternative to a multi‐layered model, we consider a simple smooth acoustic constant‐density velocity model, which has a negative constant vertical depth gradient of the squared P‐wave slowness and is bounded by a free surface at the top and a homogeneous half‐space at the bottom. The exact solution involves Airy functions and provides an analytical expression for the dispersion equation. If the ratio is sufficiently small, the dispersion curves can be picked from the seismic data and inverted for the continuous P‐wave velocity profile. The potential advantages of our model are its low computational cost and the fact that the result can serve as a smooth starting model for full‐waveform inversion. For the latter, a smooth initial model is often preferred over a rough one. We test the inversion approach on synthetic elastic data computed for a single‐layer P‐wave model and on field data, both with a small ratio. We find that a single‐layer model can recover either the shallow or deeper part of the profile but not both, when compared with the result of a multi‐layer inversion that we use as a reference. An extension of our analytic model to two layers above a homogeneous half‐space, each with a constant vertical gradient of the squared P‐wave slowness and connected in a continuous manner, improves the fit of the picked dispersion curves. The resulting profile resembles a smooth approximation of the multi‐layered one but contains, of course, less detail. As it turns out, our method does not degrade as gracefully as, for instance, diving‐wave tomography, and we can only hope to fit a subset of the dispersion curves. Therefore, the applicability of the method is limited to cases where the ratio is small and the profile is sufficiently simple. A further extension of the two‐layer model to more layers, each with a constant depth gradient of the squared slowness, might improve the fit of the modal structure but at an increased cost.     

Inversion of local S-wave velocity structures from average H/V ratios, and their use for the estimation of site-effects

H/V spectral ratios from microtremors areused to retrieve the S-velocity structurefrom a single ambient vibration record, byusing its relation to the ellipticity ofthe fundamental mode Rayleigh wave and theamplitude of observed H/V ratio.Constraints are needed in order to restrictthe possible range of solutions, and theinversion is applied to sites where thethickness of the unconsolidated sedimentsis approximately known from boreholeinformation. Within the uncertainty, theinverted structures agree well with theresults from other S-wave measuringtechniques such as downhole and cross-holemeasurements, and the analysis of ambientvibrations measured on an array.The influence of the inversion uncertaintyon site-amplification estimates forearthquakes is then investigated. For allinverted models, site response is computedfor a large number of events, which allowsto define the uncertainty by the aprioriunknown source position and mechanism of afuture earthquake. In most cases thevariability between the results obtainedfor the different models is much smallerthan the variability introduced by theunknown source position. The accuracy withwhich S-wave velocity structures can beretrieved from observed H/V ratios istherefore sufficient for an application ofthe method in seismic hazard analysis for aspecific site.     

An empirical method to estimate shear wave velocity of soils in the New Madrid seismic zone

In this study, a set of charts are developed to estimate shear wave velocity of soils in the New Madrid seismic zone (NMSZ), using the standard penetration test (SPT) N values and soil depths. Laboratory dynamic test results of soil samples collected from the NMSZ showed that the shear wave velocity of soils is related to the void ratio and the effective confining pressure applied to the soils. The void ratio of soils can be estimated from the SPT N values and the effective confining pressure depends on the depth of soils. Therefore, the shear wave velocity of soils can be estimated from the SPT N value and the soil depth. To make the methodology practical, two corrections should be made. One is that field SPT N values of soils must be adjusted to an unified SPT N′ value to account the effects of overburden pressure and equipment. The second is that the effect of water table to effective overburden pressure of soils must be considered. To verify the methodology, shear wave velocities of five sites in the NMSZ are estimated and compared with those obtained from field measurements. The comparison shows that our approach and the field tests are consistent with an error of less than of 15%. Thus, the method developed in this study is useful for dynamic study and practical designs in the NMSZ region.     

偶极横波远探测在裸眼井及套管井中接收波场的方位响应特征

偶极横波远探测技术的快速发展及其在裸眼和套管井中应用的需求增加使得研究井中远探测波场的方位特征和接收响应具有重要意义.将远探测声场看作是声源在反射体一侧的镜像点的辐射声场并对其做柱面波展开,得到了充液裸眼和套管井中偶极横波方位远探测接收声场的渐近解.据此对声场在井内流体中产生的径向位移和声压进行了模拟分析,深入研究了接收器偏心距、声源频率和地层类型对井中方位接收波场的影响,并对裸眼和套管井中的响应特征进行了对比,预示了快速和慢速地层条件下声场方位响应中的180°相位反转现象.渐近解析解与三维有限差分数值解的结果对比证实了这一现象,同时也验证了解析解的正确性和普适性.结果表明：接收器偏心距、声源频率和地层类型是井中接收声场方位响应特征的主要影响因素;SH横波入射引起的井内流体的径向位移和声压方位响应特征基本一致,而SV横波入射时二者特征却有较大差异;因此,接收信号中的SV分量有助于识别反射体方位;相对于裸眼井,套管井中接收声场的方位灵敏度更高,更有利于识别井外反射体的方位.本文的分析结果为偶极横波方位远探测技术的进一步发展和应用提供了理论支持.

     

Evaluation of shear wave velocity profile using SPT based uphole method

The uphole method is a field seismic test which uses receivers on the ground surface and an underground source. A modified form of the uphole method is introduced in order to obtain efficiently the shear wave velocity (V_S) profile of a site. This method is called the standard penetration test (SPT)-uphole method because it uses the impact energy of the split spoon sampler in the SPT test as a source. Since the SPT-uphole method can be performed simultaneously with the SPT test it is economical and not labor intensive compared to the original uphole methods which use small explosives or a mechanical source. Field testing and interpretation procedures for the proposed method are described. To obtain reliable travel time information of the shear wave, the first peak point of the shear wave using two component geophones is recommended. Through a numerical study using the finite element method (FEM), the procedure of the proposed method was verified. Finally, the SPT-uphole method was performed at several sites, and the field applicability of the proposed method was verified by comparing the V_S profiles determined by the SPT-uphole method with the profiles determined by the downhole, the spectral analysis of surfaces waves (SASW) method and from the SPT-N values.