Using Finite-difference Modelling with Stochastic Stratigraphy to Simulate 3D VSP Acquisition in the Southern North Sea

We present a case study of simulating 3D VSP acquisition using visco-acoustic finite-difference methods and a complex realistic earth model. The VSP covers an area in which the quality of the surface seismic image is poor because of complex dolomite bodies in the overburden. The velocity model was built in three stages. High frequency components of the layered model were generated automatically using a probabilistic method and were merged with a background trend. Layers faulted in a checkerboard pattern were then inserted to assess the ability to image small-scale faults at the target. Several source configurations were simulated for a fixed set of receivers placed along the proposed wellbore. Images were obtained from simulated shot records by Reverse Time Migration of upgoing waves using a smooth velocity model. Results were then analyzed for image quality by extracting attributes along target horizons. Based on this study we concluded that a minimum 4 km offset of the source on the surface is required to sufficiently image the target. Stochastic stratigraphy was effective in rapidly generating complex and realistic models of the subsurface and enhanced our ability to understand the value of a 3D VSP survey for imaging.