共查询到20条相似文献，搜索用时 15 毫秒
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Synthetic seismograms can be very useful in aiding understanding of wave propagation through models of real media, verification of geologic models derived from interpretation of field seismic data, and understanding the nature and complexity of wave phenomena. If meaningful results are to be obtained from synthetic seismograms, the method of their computation must, in general, include three-dimensional geometrical spreading of wavefronts associated with highly concentrated (i.e., point) sources. The method should also adequately represent the seismic response of solid-layered media by including enough primaries, multiples, and converted phases to accurately approximate the total wavefield. In addition to these features, it is also very helpful, although not always essential, if the method of seismogram computation provides for explicit identification of wave type and ray path for each arrival. Various seismograms, computed via asymptotic ray theory and an automatic ray generation scheme, are presented for a highly simplified North Sea velocity structure. This is done to illustrate the importance of the above features and to demonstrate the inadequacy of the plane-wave synthesis method of seismogram computation for point sources and the limitations of acoustic models of solid-layered media. 相似文献
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复地震道分析又称三瞬分析,该分析方法可将反映地震信号局部变化情况的地震波的瞬时振幅、瞬时相位和瞬时频率等信息分离开.本文应用Hilbert变换求解虚地震记录,用复地震道分析方法求取"三瞬"信息,并用该方法计算了理论合成地震记录的瞬时振幅、瞬时相位和瞬时频率,获得了较好的效果.同时,本文也利用该方法对某区块实际地震资料进行了处理,结果表明,复地震道分析方法获得的"三瞬"信息可反映地震信号的局部变化,有助于进行地震薄互层分析,并能提高数据的解释精度. 相似文献
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Kaja Pietsch Paweł Marzec Marcin Kobylarski Tomasz Danek Andrzej Leśniak Artur Tatarata Edward Gruszczyk 《Acta Geophysica》2007,55(2):191-208
The thin-layer build of the Carpathian Foredeep Miocene formations and large petrophysical parameter variation cause seismic
images of gas-saturated zones to be ambiguous, and the location of prospection wells on the basis of anomalous seismic record
is risky. A method that assists reservoir interpretation of standard recorded seismic profiles (P waves) can be a converted wave recording (PS waves).
This paper presents the results of application of a multicomponent seismic survey for the reservoir interpretation over the
Chałupki Dębniańskie gas deposit, carried out for the first time in Poland by Geofizyka Kraków Ltd. for the Polish Oil and
Gas Company. Seismic modeling was applied as the basic research tool, using the SeisMod program based on the finite-difference
solution of the acoustic wave equation and equations of motion. Seismogeological models for P waves were developed using Acoustic Logs; S-wave model (records only from part of the well) was developed on the basis of theoretical curves calculated by means of the
Estymacja program calibrated with average S-velocities, calculated by correlation of recorded P and PS wavefields with 1D modeling.
The conformity between theoretical and recorded wavefields makes it possible to apply the criteria established on the basis
of modeling for reservoir interpretation. Direct hydrocarbon indicators (bright spots, phase change, time sag) unambiguously
identify gas-prone layers within the ChD-2 prospect. A partial range of the indicators observed in the SW part of the studied
profile (bright spot that covers a single, anticlinally bent seismic horizon) points to saturation of the horizon. The proposed
location is confirmed by criteria determined for converted waves (continuous seismic horizons with constant, high amplitude)
despite poorer agreement between theoretical and recorded wavefields. 相似文献
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—Comparison of deep seismic sounding (DSS) results of different profiles across the Narmada-Son Lineament (NSL), India indicates the anomalous nature of the crust along the Ujjain-Ma han profile. Forward travel time and synthetic seismogram modeling, using normalized record sections of refraction and wide angle reflection data acquired along the Ujjain-Mahan deep seismic sounding profile across NSL, brings into focus the presence of high velocity (7.0–7.3?km/s) subhorizontal layers from a depth of 8–12?km down to Moho. The tectonic implication of such reflections (layering in the crust) is discussed. The two fault zones, reported by earlier workers, flanking the rift might have acted as feeders for the mantle material to intrude into the middle and lower crustal columns. 相似文献
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In this study we derive expressions for particle displacement or particle velocity anywhere inside a stratified earth and at its surface due to horizontal torque source located in the top layer. Equivalently, invoking Green's function reciprocity theorem, the solution applies also to the case of a surface or subsurface source when the resulting displacement or velocity is measured within the top layer. In order to evaluate the closed-form analytical solution economically and accurately it is advisable to introduce inelastic attenuation. Causal inelastic attenuation also lends the necessary realism to the computed seismic trace. To provide proof that the analytical solution is indeed correct and applicable to the multilayer case, a thick uniform overburden was assumed to consist of many thin layers. The correctness of the computed particle velocity response can be very simply verified by inspection. The computed response can also serve as a check on other less accurate methods of producing synthetic seismograms, such as the techniques of finite differences, finite elements, and various sophisticated ray-tracing techniques. It is not difficult to construct horizontal surface torque source. It appears that such source is well suited for seismic exploration in areas with a high-velocity surface layer. A realistic source function is analyzed in detail and normalized displacement response evaluated at different incidence angles in the near and the far fields. In an effort to distinguish the features of an SH torque seismogram from a pressure seismogram two models with identical layerings and layer parameters have been set up. As expected the torque seismogram is very different from the compressional seismogram. One desirable feature of a torque seismogram is the fast decay of multiples. Exact synthetic seismograms have many uses; some of them, such as the study of complex interference phenomena, phase change at wide angle reflection, channeling effects, dispersion (geometrical and material), absolute gain, and inelastic attenuation, can be carried out accurately and effortlessly. They can also be used to improve basic processing techniques such as deconvolution and velocity analysis. The numerical evaluation of the analytical solution of the wave equation as described in this paper has a long history. Most of the work leading to this paper was carried out by one of us (M. J. K.) in the years 1957 to 1968 at the Geophysical Research Corporation. However, the full testing of the various computer codes was carried out only very recently at the Phillips Petroleum Company. 相似文献
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Site characterization for design of deep foundations is very crucial, as unanticipated site conditions still represent significant problems and disputes occur during construction. Traditional surface-based geophysical methods, which use wave velocity dispersion or first-arrival times, have been widely used recently to assess spatial variation; however they cannot well characterize reverse profiles or buried low-velocity zones. For better characterization of these challenging site conditions, a full waveform inversion based on Gauss–Newton method is presented. The inversion scheme is based on a finite-difference solution of the 2-D elastic wave equation in the time domain. The strength of this approach is the ability to generate all possible wave types of seismic wavefields that are then compared with observed data to infer complex subsurface properties. Virtual sources and reciprocity of wavefields are used for calculation of partial derivative wavefields to reduce computer time. Cross convolution between observed and estimated wavefields are also employed to allow the technique to be independent of the source signatures. The capability of the presented technique is tested with both synthetic and real experimental data sets. The inversion results from synthetic data show the ability of characterizing anomalies of low- and high-velocity zones, and the inversion results from real data are generally consistent with SPT N-value, including the identification of a buried low-velocity layer. 相似文献
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Oziel Souza de Araújo Eduardo Chemas Hindi Augustinho Rigoti Fábio Henrique Rigoti 《Geophysical Prospecting》2019,67(7):1965-1976
Geophysical investigations using conventional techniques applied to groundwater exploration can often present strong limitations involving high financial costs, complex acquisition logistics and high ambiguity in results. Dispersion of the electric current flow, induced polarization) effects, cultural noises and shallow lateral heterogeneities represent the main problems faced by geoelectric methods in these types of surveys. Moreover, elements such as intrusions and mineralization at different depths may be responsible for signal attenuation as well as high resistivity in unsaturated zones and complex three-dimensional formations or clayey zones cause variations in the electric current. The focused source electromagnetic and differentially normalized method approaches can help to solve some these issues. Aiming at a higher signal-to-noise ratio, the focused source electromagnetic method and approaches of the differentially normalized method, first applied to petroleum exploration, are tested on a groundwater target, in a karst environment sectioned by a diabase dyke. We performed the processing and analysis on real IP resistivity profiling data acquired with two-way dipole-dipole array, guided by magnetic data acquired on the same profile, mapping a diabase dyke. The inversion of focused source electromagnetic method/differentially normalized method was not performed, instead that we converted the induced polarization–resistivity data to a differential signal to qualitatively prove the presence of aquifer. Joint interpretation of focused source electromagnetic method curves and inverted two-dimensional induced polarization–resistivity sections allowed for precise delineation of a conductive zone associated with the karst aquifer, le magnetics allowed for the definition of a neighbour dyke. The techniques have great potential in the aid of groundwater exploration, contributing substantially to the reduction of interpretation ambiguity. Focused source electromagnetic method/differentially normalized method/ approaches show that a simple linear combination of the conventional geoelectric data is able to remove the geological noise and provide the vertical focusing of the electric current. 相似文献
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The phase and group velocity surfaces are essential for wave propagation in anisotropic media. These surfaces have certain features that, especially, for shear waves result in complications for modelling and inversion of recorded wavefields. To analyse wave propagation in an anisotropic model, it is important to identify these features in both the phase and group domains. We propose few characteristics for this analysis: the energy flux angle, decomposed in the polar and azimuth angle correction angles and enhancement factor, which is able to characterize both singularity points and triplication zones. The very simple equation that controls the triplications is derived in the phase domain. The proposed characteristics are illustrated for elastic and acoustic anisotropic models of different symmetry classes. 相似文献
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在各向异性地震波场中,qP波与qS波常常是耦合在一起的.多分量地震数据处理中一个关键环节就是波型分离(即模式解耦),以纵波成分为主的常规单分量地震数据的成像则需要合理描述标量qP波的传播算子.本文作者曾构建了在运动学上同弹性波动方程等价,动力学上突出标量qP波的伪纯模式波动方程.为了彻底消除qS波残余,本文根据波矢量与qP波偏振矢量之间的偏差,提出从伪纯模式波场提取纯模式标量qP波的方法.数值分析展示了投影偏差算子在波数域和空间域的特征.基于不同复杂程度理论模型的试验结果表明,联合"伪纯模式传播算子"与"投影偏差校正"可为各向异性介质分离模式波场传播过程提供一种简便的描述工具. 相似文献
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Wavefield extrapolation and prestack depth migration in anelastic inhomogeneous media 总被引：6，自引：0，他引：6
Wavefield depth extrapolation and prestack depth migration in complex anelastic media are studied. Kjartansson's frequency‐independent Q law is used to describe the absorption of seismic energy. The macromodel used is analogous to the macromodel used for current migration schemes except that an additional frequency‐independent Q macromodel needs to be provided. Absorption in the forward one‐way propagator is introduced by assuming a complex phase velocity, and the inverse one‐way propagator is obtained using the reciprocity theorem for one‐way wavefields in dissipative media. The stability of the inverse propagator is achieved by limiting the angle of propagation of wavefields. A table‐driven explicit operator scheme for imaging complex 2D anelastic media is presented. High‐accuracy, short convolution operators are designed by the weighted least‐squares method, and two kinds of imaging conditions are proposed. Numerical examples of depth extrapolation in laterally varying media, the migration of a spatial impulse with dispersion as well as shot record depth migration demonstrate the potential of the proposed explicit forward operator, the explicit inverse operator and the prestack depth migration scheme, respectively. 相似文献
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尽管叠前逆时偏移成像精度高,但仅针对单一纵波的成像也可能形成地下介质成像盲区,由于基于弹性波方程的逆时偏移成像可形成多波模式的成像数据,因此弹性波逆时偏移成像可提供更为丰富的地下构造信息.本文依据各向同性介质的一阶速度-应力方程组构建震源和检波点矢量波场,再利用Helmholtz分解提取纯纵波和纯横波波场,使用震源归一化的互相关成像条件获得纯波成像,避免了直接使用坐标分量成像而引起的纵横波串扰问题.针对转换波成像的极性反转问题,文中提出一种共炮域极性校正方法.为有效节约存储成本,也提出一种适用于弹性波逆时偏移的震源波场逆时重建方法,在震源波场正传过程中,仅保存PML边界内若干层的速度分量波场,进而逆时重建出所有分量的震源波场.本文分别对地堑模型和Marmousi2模型进行了弹性波逆时偏移成像测试,结果表明:所提出的共炮域极性校正方法正确有效,基于波场分离的弹性波逆时偏移成像的纯波数据能够对复杂地下构造准确成像. 相似文献
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赵荣国 《地震地磁观测与研究》1994,15(1):21-37
本文是１９９３年大震速报培训班讲课的一部分。主要讨论了仅用某一地震台的地震图分析远震和极远震震相方法问题。包括地震波和震相的异同、地震图的复杂性、震相特征和分析方法。讲座的第一、二章刊登在本刊１９９３年第６期上。此处为接续。 相似文献
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The scattering of elastic energy by random clusters of fractures and/or cavities in a massive rock is studied. The interpretation of the scattered seismic response reveals crucial information about the clusters of inhomogeneities (fractures/cavities), which may correspond to reservoirs. The study is based on a new two‐dimensional numerical‐modelling method that relaxes the constraints on the location and orientation of the inhomogeneities, accounts for inhomogeneities that have almost no volume but a finite surface area (fractures) and improves the accuracy of the calculation when the size of the inhomogeneities is comparable to the mesh size. It is shown that the nature of the seismic response of zones of diffuse fracturing and/or cavities is associated with the non‐uniformity of micro‐inhomogeneities in such zones; accumulations of these micro‐inhomogeneities are known as clusters. The relationship between the non‐uniformity of micro‐inhomogeneities and the strength of the seismic response has been established and measured. Considerable differences in the structure of the seismic response of zones of diffuse fracturing and diffuse cavities have been identified. Converted PS‐waves dominate in the scattered wavefield associated with fractures. This is explained, as the modelling results show, by a greater transparency of fluid‐filled fractures, which reduces the reflected energy of compressional waves. The wavefield associated with cavities is characterized by the predominance (in terms of strength) of compressional PP‐waves. The strength of converted PS‐waves in the scattered wavefields for both media is approximately the same. On the whole, according to the results of the modelling, the energy of the scattered response of fractured reservoirs is considerably less (about two times) than that of cavernous reservoirs. 相似文献
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A synthetic seismogram that closely resembles a seismic trace recorded at a well may not be at all reliable for, say, stratigraphic interpretation around the well. The most accurate synthetic seismogram is, in general, not the one that displays the smallest errors of fit to the trace but the one that best estimates the noise on the trace. If the match is confined to a short interval of interest or if the seismic reflection wavelet is allowed to be unduly long, there is considerable danger of forcing a spurious fit that treats the noise on the trace as part of the seismic reflection signal instead of making a genuine match with the signal itself. This paper outlines tests that allow an objective and quantitative evaluation of the accuracy of any match and illustrates their application with practical examples. The accuracy of estimation is summarized by the normalized mean square error (NMSE) in the estimated reflection signal, which is shown to be (/n)(PN/PS) where PS/PN is the signal-to-noise power ratio and n is the spectral smoothing factor. That is, the accuracy varies directly with the ratio of the power in the signal (taken to be the synthetic) to that in the noise on the seismic trace, and the smoothing acts to improve the accuracy of the predicted signal. The construction of confidence intervals for the NMSE is discussed. Guidelines for the choice of the spectral smoothing factor n are given. The variation of wavelet shape due to different realizations of the noise component is illustrated, and the use of confidence intervals on wavelet phase is recommended. Tests are described for examining the normality and stationarity of the errors of fit and their independence of the estimated reflection signal. 相似文献
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波动方程宽角抛物逼近得到的通常是非常系数的单程波传播算子,其系数是速度横向变化的函数,因此需要利用有限差分(FD)进行数值实施. 通过对Lippmann Schwinger单程波动积分方程的退化核逼近,本文研究了一类宽角退化算子的偏移成像. 这种退化偏移算子只用快速Fourier变换进行波场延拓,将常规的Fourier分裂步地震偏移方法(SSF)推广适应强速度横向变化介质和大角度传播波场. 退化的Fourier偏移算子通过在两个分裂步项之间作波数域线性插值来实现波场延拓,每延拓一层需要比常规的SSF地震偏移方法多一次快速Fourier变换(FFT). 通过SEG/EAGE盐丘模型和实际地震资料的应用表明,退化Fourier偏移算子能很好地对盐下的陡倾角断层和实际地震剖面上的复杂小断块和大断裂地质构造成像. 相似文献
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采用弹性波全波形反演方法精确重建深部金属矿多参数模型,建模过程采用基于地震照明的反演策略.首先给出基于照明理论的观测系统可视性定义,利用可视性分析构建新的目标函数,对反演目标可视性较高的炮检对接收到的地震记录在波场匹配时占有更高的权重,确保了参与反演计算中的地震数据的有效性;其次将给定观测系统对地下介质的弹性波场照明强度作为优化因子,根据地震波在波阻抗界面处的能量分配特点,自适应补偿波场能量分布和优化速度梯度,以提高弹性波全波形反演过程的稳定性和反演结果的精度.理论模型和金属矿模型反演试验结果表明,基于可视性分析和能量补偿的反演策略可以使弹性波全波形反演更快地收敛到目标函数的全局极小值,获得适用于金属矿高分辨率地震偏移成像的多参数模型. 相似文献
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Synthesis of a seismic virtual reflector* 总被引：1，自引：0，他引：1
We describe a method to process the seismic data generated by a plurality of sources and registered by an appropriate distribution of receivers, which provides new seismic signals as if in the position of the receivers (or sources) there was an ideal reflector, even if this reflector is not present there. The data provided by this method represent the signals of a virtual reflector. The proposed algorithm performs the convolution and the subsequent sum of the real traces without needing subsurface model information. The approach can be used in combination with seismic interferometry to separate wavefields and process the reflection events. The application is described with synthetic examples, including stationary phase analysis and with real data in which the virtual reflector signal can be appreciated. 相似文献