基于二维三分量伪谱法模拟数据的EDA介质中横波分裂研究
摘要
为了检测定向裂隙介质中横波分裂的方位属性特征,分析地震属性随裂隙密度和方位变化,采用人工吸收边界和反周期扩展边界,用伪谱法获得不同裂隙密度和不同方位地质模型三分量地面记录;应用时频分析和剪切波偏振分析研究由于裂隙方位和密度引起的横波分裂.结果显示,裂隙密度和方位决定着横波分裂的时差和偏振.快慢横波的延迟时间随裂隙密度增大而增加,不同方位相同裂隙密度的横波分裂时差有微小的变化.在45°方位检测时间延迟时间最大.通过时频分析,可以看到不同方位的瞬时主频有显著的变化,在横波分裂处瞬时主频有明显变化.因此,瞬时主频和快横波的偏振以及延迟时间可以作为裂隙方位和密度的指示.
In order to evaluate the detecting performance of azimuthal dependence of shear wave splitting on preferred oriented cracks/fractures,we made analyses of seismic attributes variations with respect to crack/fracture density and orientation. A set of three-component gathers are obtained from two-dimensional modeling with the popular pseudo-spectral wavefield simulation method. In our modeling,the absorbing boundary and antiperiodic extension method are applied to suppress surface-observed synthetic seismograms from the layered models with different orientation azimuth and density of cracks/fractures. Then,the time-frequency analysis and splitting shear wave's polarization check techniques are adopted to understand azimuthal dependence of shear wave splitting on preferred oriented cracks/fractures. The results demonstrate that the orientation and density of cracks/fractures determine the delay time and polarization of shear-wave splitting. With density of cracks/fractures increasing,the delay time of fast and slow shear wave increases. The delay time varies slightly with crack orientation,and reaches maximum at 45°. On the other hand,by applying time-frequency analysis,we obtain that instantaneous dominant frequency is obviously different for different cracks/fractures orientation and it changes sharply with the shear wave splitting. Thus,the azimuthal variation of instantaneous amplitude and frequency as well as the delay time and fast splitting shear wave polarization can be used as seismic signatures of azimuth and density of orientated cracks/fractures.
In order to evaluate the detecting performance of azimuthal dependence of shear wave splitting on preferred oriented cracks/fractures,we made analyses of seismic attributes variations with respect to crack/fracture density and orientation. A set of three-component gathers are obtained from two-dimensional modeling with the popular pseudo-spectral wavefield simulation method. In our modeling,the absorbing boundary and antiperiodic extension method are applied to suppress surface-observed synthetic seismograms from the layered models with different orientation azimuth and density of cracks/fractures. Then,the time-frequency analysis and splitting shear wave's polarization check techniques are adopted to understand azimuthal dependence of shear wave splitting on preferred oriented cracks/fractures. The results demonstrate that the orientation and density of cracks/fractures determine the delay time and polarization of shear-wave splitting. With density of cracks/fractures increasing,the delay time of fast and slow shear wave increases. The delay time varies slightly with crack orientation,and reaches maximum at 45°. On the other hand,by applying time-frequency analysis,we obtain that instantaneous dominant frequency is obviously different for different cracks/fractures orientation and it changes sharply with the shear wave splitting. Thus,the azimuthal variation of instantaneous amplitude and frequency as well as the delay time and fast splitting shear wave polarization can be used as seismic signatures of azimuth and density of orientated cracks/fractures.
引文
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[20]Arthur E B.Instantaneous spectral bandwidth and dominant frequency with application to seismic reflection data.Geophysics,1993,58(3):419~427
[21]汪和杰,董敏煜.EDA介质中的弹性波.石油地球物理勘探,1994,29(6):706~712Wang HJ,Dong M Y.Elastic wave in EDA medium.Oil Geophysical Prospecting(in Chinese),1994,29(6):706~712
[2]Yang D H,Liu E R.Zhang ZJ,et al.Finite-difference modelingin two-dimensional anisotropic media using a flux-corrected transport technique.Geophysical Journal International,2002,148(2):320~328
[3]Yang D H,Teng J W,Zhang Z J,et al.A nearly analytic discrete methodfor acoustic and elastic wave equations in anisotropic media.Bulletin ofthe Seismological Society ofAmerica,2003,93(2):882~890
[4]Zhang ZJ,He Q D,Teng J W,et al.Simulation of3-component seismic records in a2-dimensional transversely isotropic media with finite-difference.Can.J.Expl.Geophys.,1993,29:51~58
[5]郑海山,张中杰.横向各向同性(VTI)介质中非线性地震波场模拟.地球物理学报,2005,48(3):660~671Zheng HS,Zhang Z J.Synthetic seismograms of nonlinear seismic waves in anisotropic(VTI)media.Chinese J.Geophys.(in Chinese),2005,48(3):660~671
[6]杨顶辉.双相各向异性介质中弹性波方程的有限元解法及波场模拟.地球物理学报,2002,45(4):575~583Yang D H.Finite element method of the elastic wave equation and wavefield simulation in two-phase anisotropic media.Chinese J.Geophys.(in Chinese),2002,45(4):575~583
[7]Liu E R,Zhang Z J.Numerical study of elastic wave scattering by cracks or inclusions using the boundary integral equation method.Journal ofComputational Acoustics,2001,9(3):1039~1054
[8]Takashi Furumura,Hiroshi Takenaka.A wraparound elimination technique for the pseudospectral wave synthesis using an antiperiodic extension of the wavefield.Geophysics,1995,60(1):302~307
[9]Dan D,Kosloff,Edip Baysal.Forward modeling by a Fourier method.Geophysics,1982,47(10):1402~1412
[10]张文生,何樵登.二维横向各向同性介质的伪谱法正演模拟.石油地球物理勘探,1998,33(3):310~319Zhang WS,He Q D.Pseudo-spectral forward modeling in2-D transversellyisotropic medium.Oil Geophysical Prospecting,1998,33(3):310~319
[11]侯安宁,何樵登.各向异性介质中弹性波传播特征的伪谱法模拟研究.石油物探,1995,34(2):36~45Hou AN,He Q D.Study on characteristics of elastic wave propagationin pseudo-spectral modeling.Geophysical Prospectingfor Petrolum(in Chinese),1995,34(2):36~45
[12]何樵登,张中杰.横向各向同性介质中地震波及其数值模拟.长春:吉林大学出版社,1996He QD,Zhang Z J.Waves in Transversely Isotropic Medium and Numerical Modelling(in Chinese).Changchun:Jilin University Press,1996
[13]Hudson J A.A high order approximation to the wave propagation constants for a cracked solid.Geophys J.R.astr Soc.,1986,87:265~274
[14]Crampin S,Chesnokov E M,Hipkin R G.Seismic anisotropy—the state of the art:II.Geophys.J.R.astr.Soc.,1984,76(1):1~16
[15]Cerjan C,Kosloff D,Kosloff R,Reshef M.Anonreflecting boundary condition for discrete acoustic and elastic wave equations.Geophysics,1985,50:705~708
[16]张中杰,滕吉文,何樵登等.三分量地震资料中各向异性检测.长春地质学院学报,1994,24(1):77~83Zhang ZJ,Teng J W,He Q D,et al.Detection of anisotropy in3-component seismic data.Journal of Changchun University of Earth Sciences(in Chinese),1994,24(1):77~83
[17]Grossmann A,Kronland-Martinent R,Morlet J.Reading and understanding continueous wavelet transforms.In:Wavelets,Time-Frequency Method and Phase Space.1st Int.Wavelets Conf.,Marseille,1989.2~20
[18]Farge M.Wavelet transforms and their applications to turbulence.Ann.Rev.Fluid Mech.,1992,24:395~457
[19]高静怀,汪文秉,朱光明.小波变换与瞬时特征分析.地球物理学报,1997,40(6):821~832Gao J H,Wang WB,Zhu G M.Wavelet transformandinstantaneous attributes analysis.Chinese J.Geophys.(in Chinese),1997,40(6):821~832
[20]Arthur E B.Instantaneous spectral bandwidth and dominant frequency with application to seismic reflection data.Geophysics,1993,58(3):419~427
[21]汪和杰,董敏煜.EDA介质中的弹性波.石油地球物理勘探,1994,29(6):706~712Wang HJ,Dong M Y.Elastic wave in EDA medium.Oil Geophysical Prospecting(in Chinese),1994,29(6):706~712
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