起伏地表稳相偏移方法及其在准噶尔盆地高密度地震勘探中的应用

Stationary-phase prestack time migration for rugged topography and application to high density seismic exploration in Junggar Basin

稳相偏移方法为基于菲涅耳带的散射叠加偏移方法.叠前时间偏移实践中,稳相偏移对振幅保真、偏移噪声压制、陡倾角构造正确成像以及计算效率提升均有较大帮助.基于浮动基准面假设,提出了起伏地表倾角道集计算方法.菲涅耳带可直观的展示于这一偏移域倾角道集中.采用人机交互拾取菲涅耳带边界后,可在起伏地表叠前时间偏移中结合地震道在成像点的倾角计算,剔除菲涅耳带之外的噪声干扰,从而实现起伏地表稳相偏移技术流程.准噶尔盆地阜东斜坡某试验区的单点高密度数据处理试验表明,起伏地表稳相偏移方法由于提供了空变、时变的偏移孔径,因而可兼顾陡倾角构造成像和偏移噪声的压制.进一步的分析表明,稳相偏移方法可提高单点高密度采集数据高频段信号的信噪比,为结合叠前时间偏移补偿介质对高频信号的吸收效应,提高地震成像的分辨率,进而发挥单点高密度采集数据集的宽频带优势提供重要辅助作用.

The stationary-phase migration is a diffraction summation migration method based on Fresnel zone.In practice of prestack time migration,the stationary-phase implementation is a great help for amplitude preservation,migration noise suppression,subsurface steep structures imaging as well as computation efficiency improvement.We proposed a dip-angle-gather generation method for rugged topography on the base of floating datum.Fresnel zone estimation in the dip-angle gather is one of the most intuitive approaches.After picking the boundary of Fresnel zones in a manmachine interactive way,the stationary-phase prestack time migration for rugged topography can be implemented by combining with calculations of the dip angles with respect to the seismic trace to be migrated at the imagine point.Thus,the noise outside the Fresnel zones can be eliminated.A test on a single-sensor-highdensity field dataset of FUDONG inclined slope in Junggar Basin demonstrate that the proposed stationary-phase implementation scheme is good at subsurface steep structures imaging as well as migration noise suppression because of the employment of Fresnelzone-based optimal migration aperture.The stationary-phase prestack time migtaion can improve the signal-to-noise ratio of high frequency components of the single-sensor-high-density field dataset,thus playing an important role in compensating high frequency components absorption via an actual wavepropagation path,which lead to great resolution improvement of seismic migration.Combining with the so-called deabsorptionprestacktime migration,the proposed stationary-phase prestack time migtaion can sufficiently tap the broadband advantage of the single-sensor-highdensity seismic dataset.