共查询到19条相似文献，搜索用时 822 毫秒
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为了实现三维倾斜界面真正的共反射点叠加,获得更加精确的P波速度模型,进行可靠的AVO/AVA分析,形成与三维多分量PS转换波共转换点道集配套的技术,在常速介质共反射点精确走时的基础上,推导并给出三维倾斜界面P波共反射点道集近似双曲时距关系及NMO速度;认识到近似时距在偏移距与深度比小于2时具有较高的拟合精度;指出P波共反射点道集NMO速度是P波速度、界面倾角、界面倾向和测线方位的函数,且随测线方位变化而呈现椭圆特征.与P波共中心点道集NMO速度不同.P波共反射点道集NMO速度小于介质速度.且随界面倾角增大而减小;椭圆长轴方向为倾斜界面走向方位,短轴方向为倾斜界面倾向方位. 相似文献
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在PS转换波资料处理过程中,往往需要联合P波资料提供相应的模型.在实际应用中存在P波和PS转换波层位对比困难.本文仅利用PS转换波数据,通过三维倾斜界面PS转换波CMP道集精确时距关系推导了近似时距解析表达式;分析了PS波的精确与近似时距关系随测线方位、界面倾角与倾向的变化规律及其拟合误差;并讨论了近似时距关系的三个时距参数随方位的变化特征;理论上给出描述时距的三维倾斜界面倾角、倾向、深度、纵波速度和横波速度这5个独立参数的估计方法,并通过理论模拟数据证明了该方法的可行性. 相似文献
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对于三维反射地震,文中将三维弯曲界面视为倾向和倾角变化的三维倾斜界面的包络,并依据三维倾斜界面反射提出计算三维弯曲界面P波反射时距的一种新方法。该方法基于倾角CDP理论,从界面反射点出发,给出地表CDP网格点,由检波点位置计算炮点位置,得到三维地震的炮点网格和检波点网格的分布关系,最终计算P波的三维反射时距。炮集数值模拟的结果表明,该方法有较高的计算效率,便于分析反射时距随炮点位置的变化,特别能揭示界面反射点位置和时距的关系。三维弯曲界面和三维倾斜界面的反射时距特征对比表明,仅从同一测线方位的时距难以将这两种类型的界面反射区分开来,但比较不同方位的时距差异可以解决这一问题。 相似文献
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转换波共转换点的叠加和道集选取都需要准确地计算转换点的位置.Tessmer和Behle、Taylor分别给出了水平单层介质中P SV转换波转换点坐标的解析解,由于其表达式的复杂性,在应用中几乎不被采用.在本文中,运用Snell定律重新建立了在水平反射界面上反射的P SV转换波的转换点坐标的四次方程,并严格地推导出与纵波速度、横波速度、炮检距和反射深度有关的转换点坐标的解析解,确定了惟一的解析表达式.将这一结果应用于P SV转换波的速度分析和叠加处理中.简化的公式有较好的应用价值. 相似文献
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《地球物理学进展》2016,(1)
近年来,由于勘探区域构造的逐渐复杂化,要求我们对复杂界面反射的时距特征有更进一步认识.本文在已有对复杂界面研究的基础上,结合实际3D复杂地质构造特征,对复杂条件做了两个限定:一是反射界面有界,二是复杂界面有多个不同性质界面组合而成.在这两条限定条件下,从界面反射点出发,进行炮集P波反射时距特征研究.结果表明,复杂界面反射会生产多条时距曲线,反射时距特征随测线方位的变化而变化,不同方位的时距对应的三维反射路径、反射点范围、反射点位置以及界面特征不同.其次时距曲线之间存在着比较复杂的位置关系,包括交叉、断续和无信号道等特征,这些复杂特征与组合模型中倾斜界面的倾向、倾角、模型范围和深度有关.最后对复杂模型的理论数值分析得出了反射点范围与接收点范围的对应关系,并理论证明了复杂条件下部分反射特征以及反射盲区的存在,这与实际三维地震勘探相符合.此研究有助于实际生产的观测设计及数据处理解释,对于提高三维复杂构造反射界面的认识具有理论意义. 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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多波多分量地震资料解释工作要开展好,确定PS波地震剖面上的地质层位是致关重要的内容之一.实际多波勘探工区中VSP资料常常不充足,甚至缺乏,此时借助PS波合成记录进行PS波层位标定是标定PS波层位的有效方法.为了在实际多波资料解释工作中确定好PS波地震剖面上的地质层位,对中心角度法、角道集叠加法、偏移距道集叠加法、递推法、波动方程正演及伪转换横波反射系数法6种PS波合成记录方法的原理进行了分析.依据研究区的实际地质情况建立了理论模型,对比了6种方法合成PS波记录的效果,表明各种方法合成的PS波记录的波组波系特征相似,只有少许同相轴有能量、波形差异.在实际PS波资料层位标定工作中对6种方法进行了应用研究,表明波动方程正演法、偏移距道集叠加法计算慢,不便于在层位标定工作中使用.递推法、伪转换横波反射系数法速度最快,但振幅近似精度略差.中心角度法、角道集叠加法计算速度和精度都较适应在PS波剖面层位标定工作中使用,并对研究区实际PS波资料进行了较好的标定.同时也提出了在PS波层位标定工作中发展PS波合成记录方法的一些建议,以期PS波井震资料能匹配得更好. 相似文献
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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. 相似文献
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Common‐midpoint moveout of converted waves is generally asymmetric with respect to zero offset and cannot be described by the traveltime series t2(x2) conventionally used for pure modes. Here, we present concise parametric expressions for both common‐midpoint (CMP) and common‐conversion‐point (CCP) gathers of PS‐waves for arbitrary anisotropic, horizontally layered media above a plane dipping reflector. This analytic representation can be used to model 3D (multi‐azimuth) CMP gathers without time‐consuming two‐point ray tracing and to compute attributes of PS moveout such as the slope of the traveltime surface at zero offset and the coordinates of the moveout minimum. In addition to providing an efficient tool for forward modelling, our formalism helps to carry out joint inversion of P and PS data for transverse isotropy with a vertical symmetry axis (VTI media). If the medium above the reflector is laterally homogeneous, P‐wave reflection moveout cannot constrain the depth scale of the model needed for depth migration. Extending our previous results for a single VTI layer, we show that the interval vertical velocities of the P‐ and S‐waves (VP0 and VS0) and the Thomsen parameters ε and δ can be found from surface data alone by combining P‐wave moveout with the traveltimes of the converted PS(PSV)‐wave. If the data are acquired only on the dip line (i.e. in 2D), stable parameter estimation requires including the moveout of P‐ and PS‐waves from both a horizontal and a dipping interface. At the first stage of the velocity‐analysis procedure, we build an initial anisotropic model by applying a layer‐stripping algorithm to CMP moveout of P‐ and PS‐waves. To overcome the distorting influence of conversion‐point dispersal on CMP gathers, the interval VTI parameters are refined by collecting the PS data into CCP gathers and repeating the inversion. For 3D surveys with a sufficiently wide range of source–receiver azimuths, it is possible to estimate all four relevant parameters (VP0, VS0, ε and δ) using reflections from a single mildly dipping interface. In this case, the P‐wave NMO ellipse determined by 3D (azimuthal) velocity analysis is combined with azimuthally dependent traveltimes of the PS‐wave. On the whole, the joint inversion of P and PS data yields a VTI model suitable for depth migration of P‐waves, as well as processing (e.g. transformation to zero offset) of converted waves. 相似文献
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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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Converted waves require special data processing as the wave paths are asymmetrical. The CMP concept is not applicable for converted PS waves, instead a sorting algorithm for a common conversion point (CCP) has to be applied. The coordinates of the conversion points in a single homogeneous layer can be calculated as a function of the offset, the reflector depth and the velocity ratio vP/ vs. For multilayered media, an approximation for the coordinates of the conversion points can be made. Numerical tests show that the traveltime of PS reflections can be approximated with sufficient accuracy for a certain offset range by a two-term series truncation. Therefore NMO corrections can be calculated by standard routines which use the hyperbolic approximation of the reflection traveltime curves. The CCP-stacking technique has been applied to field data which have been generated by three vertical vibrators. The in-line horizontal components have been recorded. The static corrections have been estimated from additional P- and SH-wave measurements for the source and geophone locations, respectively. The data quality has been improved by processes such as spectral balancing. A comparison with the stacked results of the corresponding P- and SH-wavefield surveys shows a good coherency of structural features in P-, SH- and PS-time sections. 相似文献
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Raphael Di Carlo Silva dos Santos João Carlos Ribeiro Cruz Manuel de Jesus dos Santos Costa 《Geophysical Prospecting》2020,68(7):2046-2063
Recently, the interest in PS-converted waves has increased for several applications, such as sub-basalt layer imaging, impedance estimates and amplitude-versus-offset analysis. In this study, we consider the problem of separation of PP- and PS-waves from pre-stacked multicomponent seismic data in two-dimensional isotropic medium. We aim to demonstrate that the finite-offset common-reflection-surface traveltime approximation is a good alternative for separating PP- and PS-converted waves in common-offset and common shot configurations by considering a two-dimensional isotropic medium. The five parameters of the finite-offset common-reflection-surface are firstly estimated through the inversion methodology called very fast simulated annealing, which estimates all parameters simultaneously. Next, the emergence angle, one of the inverted parameters, is used to build an analytical separation function of PP and PS reflection separation based on the wave polarization equations. Once the PP- and PS-converted waves were separated, the sections are stacked to increase the signal-to-noise ratio using the special curves derived from finite-offset common-reflection-surface approximation. We applied this methodology to a synthetic dataset from simple-layered to complex-structured media. The numerical results showed that the inverted parameters of the finite offset common-reflection-surface and the separation function yield good results for separating PP- and PS-converted waves in noisy common-offset and common shot gathers. 相似文献
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ZDOAN YILMAZ 《Geophysical Prospecting》1989,37(4):357-382
A conventional velocity-stack gather consists of constant-velocity CMP-stacked traces. It emphasizes the energy associated with the events that follow hyperbolic traveltime trajectories in the CMP gather. Amplitudes along a hyperbola on a CMP gather ideally map onto a point on a velocity-stack gather. Because a CMP gather only includes a cable-length portion of a hyperbolic traveltime trajectory, this mapping is not exact. The finite cable length, discrete sampling along the offset axis and the closeness of hyperbolic summation paths at near-offsets cause smearing of the stacked amplitudes along the velocity axis. Unless this smearing is removed, inverse mapping from velocity space (the plane of stacking velocity versus two-way zero-offset time) back to offset space (the plane of offset versus two-way traveltime) does not reproduce the amplitudes in the original CMP gather. The gather resulting from the inverse mapping can be considered as the model CMP gather that contains only the hyperbolic events from the actual CMP gather. A least-squares minimization of the energy contained in the difference between the actual CMP gather and the model CMP gather removes smearing of amplitudes on the velocity-stack gather and increases velocity resolution. A practical application of this procedure is in separation of multiples from primaries. A method is described to obtain proper velocity-stack gathers with reduced amplitude smearing. The method involves a t2-stretching in the offset space. This stretching maps reflection amplitudes along hyperbolic moveout curves to those along parabolic moveout curves. The CMP gather is Fourier transformed along the stretched axis. Each Fourier component is then used in the least-squares minimization to compute the corresponding Fourier component of the proper velocity-stack gather. Finally, inverse transforming and undoing the stretching yield the proper velocity-stack gather, which can then be inverse mapped back to the offset space. During this inverse mapping, multiples, primaries or all of the hyperbolic events can be modelled. An application of velocity-stack processing to multiple suppression is demonstrated with a field data example. 相似文献
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自然界的裂隙排列并非都是直立的,在复杂地壳应力作用下裂隙排列很可能是倾斜的.本文从各向异性弹性动力学基本方程出发,在特征矩阵方法基础上提出了计算任意倾斜裂隙介质水平界面上的反射、透射系数的简单方法,并利用该方法计算了倾斜裂隙介质P-P波、P-SV波和P-SH波的反透射系数.结果表明,P-P波、P-SV波和P-SH波的反透射系数与倾斜裂隙的倾角、测线方位以及偏移距这些物理参数之间存在一定的依赖关系.此外我们计算了C波的零入射相角时的反射系数,发现该反射系数跟裂隙倾角、裂隙的方位角有着明显的对应规律,且各向异性越强时,该反射系数越大.这些研究对于深入了解倾斜裂隙的动力学特征具有一定的意义. 相似文献
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Despite the complexity of wave propagation in anisotropic media, reflection moveout on conventional common-midpoint (CMP) spreads is usually well described by the normal-moveout (NMO) velocity defined in the zero-offset limit. In their recent work, Grechka and Tsvankin showed that the azimuthal variation of NMO velocity around a fixed CMP location generally has an elliptical form (i.e. plotting the NMO velocity in each azimuthal direction produces an ellipse) and is determined by the spatial derivatives of the slowness vector evaluated at the CMP location. This formalism is used here to develop exact solutions for the NMO velocity in anisotropic media of arbitrary symmetry. For the model of a single homogeneous layer above a dipping reflector, we obtain an explicit NMO expression valid for all pure modes and any orientation of the CMP line with respect to the reflector strike. The contribution of anisotropy to NMO velocity is contained in the slowness components of the zero-offset ray (along with the derivatives of the vertical slowness with respect to the horizontal slownesses) — quantities that can be found in a straightforward way from the Christoffel equation. If the medium above a dipping reflector is horizontally stratified, the effective NMO velocity is determined through a Dix-type average of the matrices responsible for the ‘interval’ NMO ellipses in the individual layers. This generalized Dix equation provides an analytic basis for moveout inversion in vertically inhomogeneous, arbitrarily anisotropic media. For models with a throughgoing vertical symmetry plane (i.e. if the dip plane of the reflector coincides with a symmetry plane of the overburden), the semi-axes of the NMO ellipse are found by the more conventional rms averaging of the interval NMO velocities in the dip and strike directions. Modelling of normal moveout in general heterogeneous anisotropic media requires dynamic ray tracing of only one (zero-offset) ray. Remarkably, the expressions for geometrical spreading along the zero-offset ray contain all the components necessary to build the NMO ellipse. This method is orders of magnitude faster than multi-azimuth, multi-offset ray tracing and, therefore, can be used efficiently in traveltime inversion and in devising fast dip-moveout (DMO) processing algorithms for anisotropic media. This technique becomes especially efficient if the model consists of homogeneous layers or blocks separated by smooth interfaces. The high accuracy of our NMO expressions is illustrated by comparison with ray-traced reflection traveltimes in piecewise-homogeneous, azimuthally anisotropic models. We also apply the generalized Dix equation to field data collected over a fractured reservoir and show that P-wave moveout can be used to find the depth-dependent fracture orientation and to evaluate the magnitude of azimuthal anisotropy. 相似文献
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Moshe Reshef 《Geophysical Prospecting》2014,62(6):1453-1467
We present an innovative approach for seismic image enhancement using multi‐parameter angle‐domain characterization of common image gathers. A special subsurface angle‐domain imaging system is used to generate the multi‐parameter common image gathers in a summation‐free image space. The imaged data associated with each common image gathers depth point contain direction‐dependent opening‐angle image contributions from all the available incident and scattered wave‐pairs at this point. Each direction‐dependent opening‐angle data can be differently weighted according to its coherency measure. Once the optimal migration velocity is used, it is assumed that in the actual specular direction, the coherency measure (semblance) along reflection events, from all available opening angles and opening azimuths, is larger than that along non‐specular directions. The computed direction‐dependent semblance attribute is designed to operate as an imaging filter which enhances specular migration contributions and suppresses all others in the final migration image. The ability to analyse the structural properties of the image points by the multi‐parameter common image gather allows us to better handle cases of complicated wave propagation and to improve the image quality at poorly illuminated regions or near complex structures. The proposed method and some of its practical benefits are demonstrated through detailed analysis of synthetic and real data examples. 相似文献