叠前逆时偏移成像及不同去噪方法效果对比研究

Effect comparison of denoising methods in pre-stack reverse time migration

逆时偏移成像是基于双程波波动方程,通过对波场正向和反向延拓来实现偏移的高精度成像方法.逆时偏移能有效利用全波场信息,且相对于单程波偏移方法而言,无传播方向限制,不需要对波场进行上、下行波的分离;将波场看作矢量波的叠加,避免了倾角限制,并能较好地实现回转波、多次波成像.在给定速度场足够准确的情况下,逆时偏移理论上能对任意复杂介质精准成像,是现在最为精确的偏移方法之一.但是,低频噪声是制约其发展的因素之一.本文在分析各种成像条件优缺点的基础上,选用归一化互相关成像条件,对多个典型模型进行逆时偏移成像测试,以验证程序的正确性;选取波场分离、Poynting矢量、拉普拉斯算子滤波等三种去噪方法,分别对组合模型和Marmousi2模型进行测试,对比三种去噪方法在叠前逆时偏移成像中的去噪效果,为实际地震资料处理提供方法借鉴.

The Reverse Time Migration（ RTM） is a high-precision imaging method based on the two-way wave equation,which is achieved by forward and reverse continuation of the wave field.Being different from the one-way wave migration method,full wave field information can be used in RTM and there is no limitation on propagating direction and not be necessary to separate up and down going waves in the wave field. The wave-field can be regarded as the superposition of vector waves, and thus it overcomes the limitation on the dip angle,and can better image the turning waves and multiple waves. When the given velocity field is accurate enough,the accurate imaging of an arbitrary complex medium can be obtained by RTM theoretically. However, the low-frequency noise is one main factor to obstruct its wide application. In this paper,on the basis of analyzing the advantages and disadvantages of various imaging conditions,the normalized cross-correlation imaging condition is used for the RTM of some typical testing models,and the imaging results indicate the method is effective. Furthermore,the wave-field separation,Poynting vector,and Laplace operator filtering methods are used in RTM for the combination and Marmousi2 models respectively. The effects of the three denoising methods are compared and these tests will provide practical suggestions on how to achieve the accurate seismic imaging by RTM.