横向各向同性介质纵波非双曲时差速度分析

P-wave nonhyperbolic moveout velocity analysis in transversely isotropic medium

在各向异性介质中,P波反射具有非双曲时差特性,地震波走时亦随排列长度的加大呈现非双曲现象。因此,常规双曲时距曲线方程已经不能满足描述地震勘探中日益复杂的地球介质模型的需求。为此,我们对双曲时距曲线进行了改进——在走时公式中加入了含炮检距的四次项,并采用分式展开法表示。改进后的表达式在形式上接近于常规地震波双曲型时距关系,清楚地描述了横向各向同性介质中速度随炮检距的变化。实例中可见其提高了复杂介质速度分析精度、改善了剖面叠加效果。

P-wave reflections in horizontally layered anisotropic media have pssessed characteristics of the nonhyperbolic moveout. The seismic traveltime also shows nonhyperbolic with increasing spread length. Therefore, the conventional traveltime equation which has hyperbolic character is insufficient to describe the more and more complicated geologic media. In this paper, a term relating to the fourth power of offset is added in the traveltime equation, and expressed by fraction expansion. The expression of improved equation is similar to the previous conventional one in its form. The velocity versus offsets in transversely isotropic medium can be clearly described. It is shown from actual example that the accuracy of velocity analysis using this method in complicated medium is improved. The stack effect is better than before.