复杂地表条件下叠前菲涅尔束偏移方法  

Prestack Fresnel beam migration method under complex topographic conditions

作　　者：杨继东[1] 黄建平[1] 王欣[1] 李振春[1] 段心意 

机构地区：[1]中国石油大学(华东)地球物理系,青岛266580

出　　处：《地球物理学报》2015年第10期3758-3770,共13页Chinese Journal of Geophysics

基　　金：国家973课题(2014CB239006;2011CB202402);国家自然科学基金(41104069;41274124);山东省自然科学基金(ZR2011DQ016);中央高校科研业务费专项基金(R1401005A)联合资助

摘　　要：高斯束偏移虽然克服了Kirchhoff偏移不能处理多波至和单程波动方程偏移不能对陡倾构造准确成像的问题,但在复杂地表条件下其偏移精度取决于所选择的初始束宽度,即当初始宽度较小时,近地表成像精度较高,但此时中深层成像质量较差;反之当初始宽度较大时,中深层成像质量提高,但近地表成像精度降低.针对高斯束偏移中深层和浅层成像精度的矛盾,本文发展了一种适用于陆地复杂地表条件的叠前菲涅尔束偏移方法.基于惠更斯-菲涅尔原理,本文首先给出了菲涅尔束的概念及其表征的格林函数,并采用有效邻域波场近似理论和反褶积成像条件,导出了复杂地表条件下叠前保幅深度偏移公式.最后,针对常规旁轴射线追踪中的数值噪音,给出了一种压制策略.同高斯束偏移相比,本文方法不仅解决了中深层和浅层成像精度的矛盾,而且提高了复杂地表条件下平面波的分解精度,使得偏移结果更加准确可靠.典型的模型算例验证了本文方法的有效性和稳健性.Gaussian-beam migration overcomes the limitation of Kirchhoff migration in imaging the multiple arrivals and of one-way wave equation migration in imaging the steep-dip structures,but its imaging accuracy depends on the initial beam width under complex topographic conditions,i.e.,that with small initial beam width,the imaging accuracy is high at near-surface but low at depth,whereas with large initial beam width,the imaging accuracy is improved in the deep but declines in the near-surface.Aiming at the problem in Gaussian-beam migration between nearsurface and deep areas,we have developed a method of prestack Fresnel beam migration method under complex topographic conditions in this paper.Based on the principle of Huygens-Fresnel,we use the first Fresnel zone radius to limit the beams′effective width and derive of the formula of Fresnel beam.And then,we adopt the steepest descent method to obtain the approximate Green function constructed with Fresnelbeams.Further,with the theory of wave field approximation in effective vicinity and deconvolution imaging condition,we obtain the prestack amplitude-preserved migration formula under complex topography conditions.Finally,aiming at the numerical noise of conventional paraxial ray tracing algorithm,we proposed an optimized strategy.Compared with Gaussian beam migration,the proposed method not only solves the contradiction of imaging accuracy in near-surface and at depth,but also improves the accuracy of plane wave decomposition,making the migration results more accurate and reliable.Typical numerical examples proved the validity and robust of our method.

关 键 词：复杂地表 高斯束 菲涅尔束 保幅成像 叠前深度偏移 

分 类 号：P631[天文地球—地质矿产勘探]