逆时深度偏移中的子波拉伸校正

Wavelet stretch correction for reverse-time migration

文中提出一种在逆时偏移的波场延拓后、应用成像条件前对地震数据进行子波拉伸校正的方法,在延拓过程中分别提取各网格点震源波场和接收点波场在成像时刻的地震子波,对其进行压缩处理,再应用归一化波场分离互相关成像条件,得到拉伸校正后的成像结果。该方法不改变成像结果的振幅与相位。其中,子波压缩计算需要的各网格点的反射角和局部地层倾角由地震波场的坡印廷矢量(Poynting vector)计算得到。数值算例表明,该方法能够校正由于反射角增大引起的子波拉伸效应,提高逆时偏移的成像品质,为AVA/AVO分析提供高精度的输入道集。

Wavelet stretch effects of large reflection angle affect seriously the image resolution of prestack reverse-time migration.According to Tygel's study,wavelet is stretched with the increase of reflection angle and local reflector dip in the vertical direction.We develop a wavelet stretch correction method after extrapolation of reverse-time migration and before applying imaging condition.First we extract wavelets in imaging time at each spatial grid point of both source wavefield and receiver wavefield,then shrink the extracted wavelets,and finally apply normalized wavefield separation cross-correlation imaging condition,and obtain stretch correction results.This method does not change the amplitude and phase of imaging.Reflect angle and local reflector dip used for shrink operation are calculated from Poynting vector of seismic wavefield.Numerical examples show that this proposed method can correct wavelet stretch effects caused by large reflection angle,improve the image quality ofprestack reverse-time migration,and provide high resolution data for AVA/AVO analysis.