The reef model has a seal with a high porosity zone associated with a natural gas or oil accumulation. This is indicated by a higher than expected reflection coefficient and a phase reversal of the signal. The reef model is shown in Figure 23. The salt structure has the feature of a slow moving slug of salt rising up through layered sediments and trapping around the flanks pockets of hydrocarbon. The signals from such an intrusion are reflected far from the expected vertical position, which makes it very difficult to correctly position the exploration well site.
Salt has a very high sound velocity, which further complicates accurate processing of the data.
The salt model is shown in Figure 26. After studying the seismic modeling process we shall find a way to process this zero-offset data and image it. This imaging process we shall call migration, the effect of moving data mispositioned in time to a place in depth.