Sub‐salt imaging using 3D pre‐stack depth migration in the UK Southern North Sea – a case history

In the UK Southern North Sea the presence of salt structures can cause considerable distortion of the sub-salt seismic image. This distortion is due to strong vertical and lateral velocity variations, which lead to the refraction of seismic waves. Pre-stack depth imaging is considered the ultimate tool for accurate delineation of sub-salt reflectors in this geological environment. To achieve the best seismic image an optimal interval velocity/depth model has to be built. This in itself presents a substantial challenge when working in areas with complicated geological structures. In this paper, an iterative process of velocity model building is presented, which closely integrates seismic data with geological information, to derive a subsurface velocity distribution that enables production of the best seismic image.