VTI介质中弹性参数地震反演方法
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摘要
根据地震波在具有垂直对称轴的横向各向同性 (VTI)介质中的运动学特征 ,应用传播时间反演方法 ,进行了水平层状VTI介质的地层弹性参数反演方法研究。在VTI介质中 ,P P波的传播时间曲线不再是双曲线 ,尤其在长排列情况下 ,已不能用二项泰勒展式精确地反演P P波的传播时间 ,用三项泰勒展式则可以达到更高精度 ;P SV波的传播时间也可用三项泰勒展式表达 ,在中等及短排列长度时可达到一定精度。对P P波、P SV波的传播时间进行三项泰勒展开时 ,它们的系数中包含了地震波的各向异性信息及垂直速度信息 ,可以为地震波的弹性参数反演提供基础。模型试验分析及江苏油田某地区的二维多波资料实际反演结果表明 ,在最大炮间距为 1.5倍地层埋深时 ,可以很精确地得到三项泰勒展式的系数 ,应用这些系数能精确反演地层弹性参数 ,包括P波、S波的垂直速度和各向异性参数。图 4表 1参 5 (杜丽英摘 )
In this paper, seismic inversion of elastic parameters in horizontally layered VTI (transverse isotropy media with vertical symmetry axis) is well studied, on the basis of seismic wave kinematics theories in transverse isotropic media with vertical symmetry axis. The reflection travel time of P-P wave deviates from hyperbolic greatly, especially for relative long spreads, so the travel time can be approximated more exactly by three terms Taylor series than by two-term Taylor series. However P-wave reflection travel time formula in the weak anisotropy hypothesis can be approximated at the highest precision even in relative moderate or long spreads. For the P-SV wave travel time, it also can be expressed exactly by a three-term Taylor series in short or moderate spreads. The three term Taylor series of P-P wave or P-SV wave reflection travel times in VTI media are the function of elastic parameters. Therefore they can be used to inverse the seismic elastic parameters. When elastic parameter inversion is done, it is known that when the maximum source-receiver distance is 1.5 times Interface depth, coefficients of three-term Taylor series could be gotten accurately, the elastic parameters including vertical velocity of P-wave, vertical velocity of S-wave and dimensionless elastic anisotropy parameters
In this paper, seismic inversion of elastic parameters in horizontally layered VTI (transverse isotropy media with vertical symmetry axis) is well studied, on the basis of seismic wave kinematics theories in transverse isotropic media with vertical symmetry axis. The reflection travel time of P-P wave deviates from hyperbolic greatly, especially for relative long spreads, so the travel time can be approximated more exactly by three terms Taylor series than by two-term Taylor series. However P-wave reflection travel time formula in the weak anisotropy hypothesis can be approximated at the highest precision even in relative moderate or long spreads. For the P-SV wave travel time, it also can be expressed exactly by a three-term Taylor series in short or moderate spreads. The three term Taylor series of P-P wave or P-SV wave reflection travel times in VTI media are the function of elastic parameters. Therefore they can be used to inverse the seismic elastic parameters. When elastic parameter inversion is done, it is known that when the maximum source-receiver distance is 1.5 times Interface depth, coefficients of three-term Taylor series could be gotten accurately, the elastic parameters including vertical velocity of P-wave, vertical velocity of S-wave and dimensionless elastic anisotropy parameters
引文
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[2]TsvankinL ,ThomsenL .Nonhyperbolicreflectionmoveoutinanisotropicmedia[J].Geophysics,1994,59:12901304.
[3] HakeH ,etal..Three termTaylorseriesfort2χ2 curvesofP waveandS waveoverlayeredtransverselyisotropicground[J ].GeophysicalProspecting,1984,32:828850.
[4] TanerMT ,KoehlerF .Velocityspectrumcomputerderivationandapplicationofvelocityfunction[J].Geophysics,1969,34:859881.
[5] TsvankinL ,ThomsenL .Inversionofreflectiontraveltimesfortransverseisotropicmedia[J].Geophysics,1995,59:12901304.
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