表驱Kirchhoff叠前时间偏移角度域成像方法

为解决垂向变速介质中的射线弯曲效应问题,获得可直接用于AVO分析和反演的角度域共成像点道集,提出了一种基于射线追踪的表驱Kirchhoff叠前时间偏移方法.方法实现的基本原理是:首先基于横向均匀介质中的反射时距关系,利用改进的两点射线追踪算法建立走时和反射张角的数值表;然后在偏移过程中利用该数值表得到成像孔径内各反射路径对应的双程走时与入射角信息;进而通过脉冲响应叠加方法得到角度域共成像点道集和偏移成像剖面.由于加权函数部分考虑了射线弯曲效应的影响,因此更有利于振幅的相对保真.角度域共成像点道集波形拉伸效应的时不变特征也有利于后续的波形恢复处理.理论模型和实际地震资料验证了该方法的可行性.

Imaging method of table-driven Kirchhoff pre-stack time migration within the angle-domain

For dealing with ray-bending effect in vertically varied velocity media and directly providing the common imaging point gathers within angle-domain for AVO analysis and inversion, the table-driven Kirchhoff pre-stack time migration based on ray tracing algorithm was proposed. The basic principles are that, according to the reflection time-distance equation in laterally homogeneous media, numerical tables of travel-time and reflecting angle are established through improved two points ray tracing algorithm, and then, during the course of migration, the information of two-way travel-time and incidence angle of each reflection path in imaging aperture can be obtained from these tables, finally, the angle-domain common-image gathers and migration sections are obtained by using the impulse responses stacking method. For partially considering the ray-bending effect into the weighting function, the imaging amplitudes should be more accurate. Moreover, the time invariant feature of waveform stretching in angle domain is beneficial to the sequent waveform correction. Test results of synthetic data and actual seismic data have verified the feasibility of this method.