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如何建立一个合理的速度模型一直困扰着叠前深度偏移。当前所使用的两个主要的偏后和叠前速度分析技术(即深度聚焦和剩余时差校正)在多数情况下得以很好的应用,但它们在复杂构造的情况下仍有一定的局限性。为强调这个问题,在保证算法对实际资料的应用有足够的稳健性的同时,我们把剩余时差分析技术推广到非均匀速度场和大倾角的一般情形。这种方法不是基于时差的解析表达式,也不要求先验模型,而是使用非均匀介质中的几何射线追踪法、层剥离偏移方法和局部波前分析法来计算出剩余速度校正量,用一种类似于层析重建的方法沿着射线路径把剩余速度校正量回射到速度模型中。和现有的偏移速度分析法相比,这种方法更具普遍性,该方法还可以大大增强计算机的能力并能够更好地应用于构造相当复杂的局部区域中。我们根据具有大速度梯度的模型来说明使用合成数据的技术方法,然后将它应用于一海上地震数据集来改善主断层的位置。
How to build a reasonable speed model has plagued the prestack depth migration. The two main post-migration and prestack velocity analysis techniques currently in use (ie depth focusing and residual time difference correction) are well suited for many situations, but they still have some limitations in the case of complex structures. To emphasize this problem, we extend the residual time difference analysis technique to the general case of non-uniform velocity field and large dip angle while ensuring that the algorithm is sufficiently robust to the practical application of the data. This method is not based on the analytical expression of the time difference, nor does it require a priori model, but uses the geometric ray tracing method, layer delamination offset method and local wavefront analysis in inhomogeneous media to calculate the residual velocity correction, A method similar to tomography reconstruction is used to reverberate the remaining velocity correction into the velocity model along the ray path. Compared with the existing migration velocity analysis method, this method is more universal, this method can also greatly enhance the computer’s ability and can be better applied to the construction of quite complex local area. We describe a technique that uses synthetic data based on a model with a large velocity gradient and then apply it to an offshore seismic data set to improve the location of the main fault.