CRP道集叠前精细处理技术应用

Application of Pre-stack Detailed Process Technique on CRP Traces Gather

随着地震反演由叠后发展到叠前,地震叠前弹性阻抗反演要求更大的入射角范围,即需要更大的偏移距范围,这就要求叠前偏移得到的共反射点(CRP)道集更加平直,动校拉伸效应更小。这就需要在叠前偏移之后,对CRP道集进行更精细的处理,尽量消除剩余时差的影响。消除剩余时差和动校拉伸效应最有效的方法是各向异性动校正,而各向异性动校正的应用需要相对正确的各向异性参数VNMO和η。本文应用一种高密度双谱扫描的方法,首先在CRP道集中进行高密度扫描,得到两个与各向异性参数有关的量值τ0和dtn,配合横向和纵向的插值、平滑,再应用位移双曲方法,将τ0和dtn转化为各向异性参数VNMO和η,最后应用各向异性动校正,最终消除由地层各向异性引起的叠前道集不平和剩余时差。本文给出了这种方法的基本流程,并在合成记录和实际数据上加以应用,都取得了较好的效果。双谱扫描的方法能够得到较为准确的各向异性参数,应用于各向异性动校正能够较好地消除剩余时差和动校拉伸对CRP道集的影响,提高有效偏移距的范围。

With the development of the post-stack seismic inversion into the pre-stack seismic inversion, the prestack seismic inversion of the elastic impedance requires a large range of incident angle, i.e. a large offset range, which means a very smooth CRP gather from the pre-migration and a small NMO stretch. So after PSTM, a detailed processing on pre-stack gathers will be carried out to reduce the impact of the residual moveout. The most effective way to reduce the residual moveout and the NMO stretch is the anisotropic NMO, which requires exact anisotropic parameters VNMO and η. In this paper, an anisotropic NMO application process is introduced, which uses the high-density dual-spectral scanning method to obtain To and dtn then converts T0 and dtn to the anisotropic parameters VNMO and η, which are required for the anisotropic NMO using the shifted hyperbola approach, with the horizontal and vertical interpolation and smoothing. These two parameters will be used in the anisotropic NMO to avoid the bad effects of anisotropy. This method is applied to the synthetic data and field data and good results are obtained, which means that this method can obtain the quite accurate anisotropic parameter, reduce bad influences of residual moveout and NMO stretch on the CRP gather and increase the range of effective offset.