地下局部角度域高斯束偏移成像

Gaussian beam migration in subsurface local angle domain

针对克希霍夫偏移无法适用于复杂构造、偏移距域偏移存在偏移假象及保幅性差的问题,本文研究了一种高效的地下局部角度域高斯束偏移方法。与常规地面偏移距域克希霍夫偏移采用地面炮检点射线追踪及走时计算不同,该方法采用地下成像点向地面进行射线追踪及走时计算,同时获得炮检点所对应地下成像点的反射角,再结合射线束偏移方法,该方法综合了射线偏移高效、高斯束偏移高精度、地下角度域成像高保幅保真的特点。模型及实际数据应用表明,该方法成像效果明显优于常规偏移距域克希霍夫成像。此外,不同于克希霍夫偏移距域偏移道集,其角度域道集为地下真共反射角道集,反应了观测系统与地下构造形态两方面的共同影响,具有更高的保幅保真度,更加适用于叠前AVA分析。

As to the problem of conventional Kirchhoff migration,namely inapplicable to complex structure,migration artifacts generated in offset domain,poor amplitude preservation,an efficient Gaussian beam migration method in subsurface local angle domain is studied in this paper.Different from conventional Kirchhoff offset domain migration,which adopts ray tracing and travel time calculation at the surface,method proposed in this paper traces ray-path and calculate travel time from subsurface imaging point to surface.Meanwhile,the local reflection angle can be obtained conveniently,and then beam migration is applied.This method incorporates high efficiency of ray migration,high accuracy of beam migration,high fidelity and amplitude preservation of subsurface angle domain imaging.Synthetic and field data tests demonstrate obviously high quality of this method compared with conventional Kirchhoff migration.Besides,migrated gather in subsurface local angle domain instead of offset domain gather of Kirchhoff migration,takes both structure and survey configuration into consideration.Hence,migrated gather of this method,which is more suitable for pre-stack AVA analysis,shares higher fidelity and amplitude preservation degree.