f Building a 3D Velocity/Depth Model from 2D Seismic Data - a Case History from the Southern gas Basin

Time to Depth in the Southern Gas basin is complicated by two factors: 1) The presence of complex salt bodies 2) Lateral variation and strong velocity contrasts within the overburden In areas where these factors exist it is necessary to use depth migration techniques in order to derive accurate interpretations of seismic structures. Simple scaling of time migrated sections will not produce accurate depth images subsalt. To produce good depth images, whether it be from post stack or pre stack depth migration techniques, it is necessary to derive as good a velocity / depth model as is possible from the data available. This can only be accomplished using a model based approach.