Pre-processing Requirements for Reverse Time Migration

Almost all conventional pre-processing is conceived of with one-way wave propagation in-mind. If we take into account the existence of two-way wave propagation arrival events, then many of the underlying assumptions of moveout behaviour implicit in some pre-processing techniques must be re-evaluated. Using 2D synthetic data, we demonstrate that the moveout behaviour of double bounce arrivals (a class of two-way propagating events) can be compromised by pre-processing designed to remove events exhibiting ‘anomalous’ moveout behaviour. These observations are of interest to us, as we are now beginning to employ two-way migration schemes to image complex structures. However, if we continue to use conventional pre-processing techniques, we run the risk of removing the very events we are trying to image. The observations made on the basis of synthetic modelled data, are extended in this work to real data examples, all from the North Sea, where in the central graben, we commonly have steep piercement salt diapir structures, which are good candidates for producing useful double bounce arrivals, which can be imaged using RTM.