3D ANISOTROPIC POST STACK IMAGING ON AN OFFSHORE AFRICA CASE-STUDY

Seismic anisotropy may degrade the quality of seismic images and cause the mispositioning of events within them. Shales have often been obse rved to be significantly anisotropic, usually with approximately hexag onal symmetry (transverse isotropy) with axis normal to the bedding pl ane. We investigate the effect of anisotropy on imaging a real data se t from offshore Africa, where there are thick shale sequences. We perf orm, in parallel, isotropic and anisotropic velocity model building an d 3D post-stack migration of the same stack volume, We observe that th e anisotropic processing improves the focussing of dipping events and that the assumption of isotropy may cause lateral and vertical displac ement of the reservoir boundaries, of around 100 and 200 meters respec tively, relative to the positions obtained with the anisotropic proces sing.