VTI介质角度域Kirchhoff叠前时间偏移方法

Angle-domain Kirchhoff prestack time migration approach in VTI media

为了支持VTI介质下的振幅随偏移距/入射角变化(AVO/AVA)技术,提出一种基于射线追踪的VTI介质角度域Kirchhoff叠前时间偏移方法。从VTI介质反射波时距关系出发,通过稳健的射线追踪算法建立反射走时和界面上入射角的数值表,进而估算射线路径对应的双程走时及入射角,利用脉冲响应叠加方法实现叠前时间偏移,得到构造图像和角度域共成像点道集。由于在振幅加权因子求取时考虑射线弯曲效应的影响,因此成像保幅性更好。所提方法获得的角度域共成像点道集同相轴平直,且有效入射角度范围更宽,有利于后续的AVO/AVA或反演处理。理论模型合成数据和实际地震资料测试结果展示了方法的优越性与实用性。

An angle-domain Kirchhoff prestack time migration approach in VTI media based on ray-tracing was presented to provide more powerful supports for AVO/AVA technique. Starting from the relationship between travel time and path length of the reflection waves in VTI media, a robust ray-tracing algorithm is developed to construct the numerical table for the travel time and incidence angle of the reflection waves on the interfaces, and then the two-way travel time and incident angle corre- sponding to the ray path can be estimated. As the result of a prestack time migration by using the impulse response superposi- tion method, the structural image and the angle domain common image gathers can be obtained. During prestaek time migra- tion, impulse responses are stacked to obtain the migrated profile and angle-domain common-image gathers. This imaging method preserves the amplitude better than the traditional methods, because it includes ray bending in the calculations of the weighting factor for amplitude preserving. The angle-domain common image gathers of this method have straight in-phase axis and a wide range of the effective incidence angle, which is beneficial to the subsequent AVO/AVA and inversion processing. The synthetic and real data tests demonstrate the validity of this approach.