基于共聚焦点道集的叠前深度偏移及其应用

PRESTACK DEPTH MIGRATION BASED ON COMMON FOCUS POINT GATHER AND ITS APPLICATION

共聚焦点叠前深度偏移是一种基于等时原理、通过检波聚焦和激发聚焦的双聚焦 (共聚型 )偏移实现地震成像的方法 ,它的关键技术是聚焦算子的计算。考虑到计算效率、精度和稳定性 ,提出了利用适于任意矩形网格的有限差分法计算聚焦算子的方法。为了提高成像信噪比和分辨率的精度 ,采用变孔径扫描叠加法获取了共聚焦点道集和聚焦点响应 ,进行了共聚焦点叠加和实现叠前深度偏移成像。模型的试算结果表明 ,利用此方法 ,在宏观速度场正确的情况下 ,能够实现地下构造的准确成像 ,尤其是明显提高了深层的信噪比。对实际资料的试处理说明 ,共聚焦点偏移的效果基本达到了利用FFD法获得叠前深度偏移的效果 ,而其计算效率主要取决于偏移孔径和计算网格的大小。

Common focus point (CFP) migration is a seismic imaging method by means of the double focusing (confocal imaging) migration (focusing in detection and focusing in emission) based on the principle of equal travel time. The key technique for the method is the computation of focusing operators. In consideration of efficiency, accuracy and stability of computation, a finite-difference method fitting to any rectangular grids for computing the focusing operators was presented. In order to enhance the signal to noise ratio and resolution of seismic imaging, the stacking method of variable-aperture scanning was adopted to obtain CFP gathers and focus-point responses and realize CFP stacking and complete CFP prestack depth migration. The computation of a sag model shows that for a correct macro velocity field, this method can realize the accurate imaging of subsurface structures and enhance significantly the signal to noise ratio in deep layers. The real seismic data processing proved that CFP migration has the same quality as FFD migration basically. The computing efficiency of CFP migration mainly depends on the sizes of migration aperture and computing grid.