Kirchhoff叠前时间偏移角度道集

Common-angle gathers based on Kirchhoff pre-stack time migration

提出三维Kirchhoff叠前时间偏移角度域共像点道集的改进算法,克服传统角度求取算法局限,可计算相对倾斜地层法线入射角;与Kirchhoff直射线叠前时间偏移求角度算法相比,本文方法考虑射线弯曲效应,包含层速度,角度范围加大,更接近真实入射角;计算走时采取弯曲射线或者适应线性横向变速介质的非对称走时等算法,角度道集在大角度处得到拉平;采用相对保幅的权因子以及覆盖次数校正技术,有利于叠前AVA反演.模型测试结果表明:叠前时间偏移角度道集,相对CMP、CRP所转化角度道集,更准确反应AVA效应;实际三维数据测试表明本文方法可以提供品质优良的角度道集,适用于AVA分析、反演,提高叠前反演分辨率.

In this paper we present the improved algorithm for common-angle gathers based on Kirchhoff pre-stack time migration. The algorithm can calculate relatively true incident angle under three-dimensional circumstance, while the traditional ray-parameter method could not handle the incident angle for the dipping events. Compared with the straight-ray Kirchhoff angle domain gathers method proposed in recent years, our method is able to extract much wider angle for taking interval velocity and ray bending effect into account. Moreover, we apply non-hyperbolic moveout equation to calculate the travel time, thus the common-angle gathers are flatter at the large angle than straight ray method. Efficient true-amplitude weighting function as well as hit-count correction is beneficial for AVA inversion. The results of synthetic model data have verified that compared with angle gathers transformed from offset to angle domain with CMP gathers and CRP gathers after migration, the common-angle gathers based on Kirchhoff pre-stack time migration have the following advantages： much more accurate incident angle, the effect of amplitude versus angle （AVA） is robust and clear. The real 3-D data test showed that the angle gathers provided with our method were beneficial for AVA analysis and AVA inversion, and could improve pre-stack inversion resolution.