Seismic imaging with primaries and multiples

Abstract

Multiples are usually considered as noise in seismic images due to their interferences with primary reflections. In recent years, new imaging methods have been developed which consider multiples as secondary sources to improve the subsurface image. In the present study, we considered the advantages related to incorporating multiple reflections into imaging process, and presented a workflow for understanding the contribution coming from the different reflection events: primaries, surface-related and internal multiples. The workflow consist of two main parts: velocity model building, and imaging with Reverse Time Migration (RTM) and Full Wavefield Migration (FWM). The workflow was tested on the synthetic and field datasets. Before actual imaging, the combination of first arrival traveltime tomography and full waveform inversion were used to obtain high-resolution velocity models. RTM imaging with primaries provides a good illuminated subsurface image with a broader frequency spectrum for the specific target interval. In the depth interval with the complex geological settings, primary images are distorted due to imperfect multiple separations. When imaging with surface-related multiples, the added value is observable at the shallow depths. However, the deeper part of surface-related multiple poorly illuminated comparing with the primary image. The added value coming from the internal multiples are clearly defined when implementing FWM on the synthetic data, in the depth interval with the notable velocity decrease FWM provides a more enhanced image. Application of FWM with 2D assumptions on the actual 3D data cannot provide a comparable image with RTM.