VTI介质P波非双曲时差分析

Analysis of P-Wave nonhyperbolic reflection moveout in VTI media

具有垂直对称轴的横向各向同性介质模型(VTI)是目前各向异性理论研究和多波多分量地震资料叠前成像处理中最常用的一种各向异性模型.VTI介质中反射P波时距曲线一般不再是双曲线.基于不同的相速度近似公式会得到不同的时距关系式.文中对几种典型的非双曲时距曲线与射线追踪得到的准确时距曲线在不同各向异性强度下进行了对比,结果表明Muir等和Stovas等提出的非双曲时距公式由于过高地考虑了横波垂直速度的影响与精确的时距曲线有很大偏差;Tsvankin等提出的弱各向异性非双曲时距公式在ε-δ<0时误差增大;Alkhalifah等提出的非双曲时距公式在大炮检距任意各向异性强度下都具有较高的精度,适于在实际资料处理中应用.

Transverse isotropy (TI) with a vertical symmetry axis (VTI) is the most common model for academic research on anisotropy and prestack imaging of multi-wave and multi-component reflection seismic data. The traveltime-distance curve of reflected P-wave in VTI media is not hyperbolic anymore. Based on different P-wave phase velocity approximations, different traveltime-distance formulae can be deduced. In this paper, we compare several traveltime approximations with exact traveltime obtained by using ray trace method on different anisotropic degree. The results show that Muir's and Stovas's traveltime approximations have large error owing to their overestimation the influence of SV-wave vertical velocity; moreover, that Tsvankin's weak anisotropic traveltime approximation has a little large error when ε-δ<0; furthermore, that Alkhalifah's traveltime approximation has enough accuracy for strong anisotropy and large offset, which is suitable for seismic data processing.