基于波动方程的广义屏叠前深度偏移

地震波传播算子的计算效率和精度是制约三维叠前深度偏移的关键因素. 广义屏传播算子(GSP, Generalized Screen Propagator)是一种在双域中实现的广角单程波传播算子. 这一方法略去了在非均匀体之间发生的交混回响,但它可以正确处理包括聚焦、衍射、折射和干涉在内的各种多次前向散射现象. 通过背景速度下的相移和扰动速度下的陡倾角校正,广义屏算子能够适应地层速度的强烈横向变化. 这种算子可以直接应用于炮集叠前偏移,通过将广义屏算子作用于双平方根方程,还可以获得一种高效率、高精度的炮检距域叠前深度偏移方法,用于二维共炮检距道集和三维共方位角道集的深度域成像. 本文首先简述了炮检距域广义屏传播算子的理论,进而讨论了共照射角成像(CAI, Common Angle Imaging)条件,由此给出各个不同照射角(炮检距射线参数)下的成像结果,进而得到共照射角像集. 由于照射角和炮检距的对应关系,共照射角像集又为偏移速度分析和AVO(振幅随炮检距变化)分析等提供了有力工具.

WAVE EQUATION BASED PRESTACK DEPTH MIGRATION USING GENERALIZED SCREEN PROPAGATOR

Computational efficiency and accuracy of seismic wave propagators are major concerns for 3 D prestack depth migration. Generalized screen propagator (GSP) is a dual domain one way propagator, which neglects reverberations between heterogeneities but correctly handles the forward multiple scattering including focusing, diffraction, refraction and interference of seismic waves. Downward continuation of the wavefield using GSP is performed with a phase shift in a background medium followed by a wide angle correction that accommodates strong lateral velocity variations. In this paper, we implement GSP in double square root equation and propose an efficient and accurate offset domain prestack depth migration method for 2 D common offset and 3 D common azimuth seismic data. Combined with common angle imaging (CAI) condition, offset domain GSP migration produces high quality images at a number of angles (or offset ray parameter values). Since offset ray parameter is proportional to angle of incidence at the reflector, CAI gathers provide a complete set of tools for migration velocity analysis and AVO analysis.