The acquisition and processing of dithered slip-sweep vibroseis data

摘要

We introduce the distance-separated dithered slip-sweep vibroseis acquisition technique with the objective of maximizing acquisition productivity for land data whilst maintaining the prestack amplitude fidelity required for detailed amplitude analysis. High productivity is achieved through the use of simultaneous sources and the technique is enabled by the large channel count; continuous recording and rule-based acquisition technologies inherent in modern land acquisition systems. The technique is very flexible and allows surveys to be designed such that the source-interference effects; after source separation; are limited to an acceptable level. Two examples illustrate the effectiveness of the technique. Firstly; we simulate a 2D, dithered data set by summing pairs of shots acquired conventionally. After separation using a sparse inversion technique; the interference noise due to simultaneous shooting is substantially eliminated and the prestack and post-stack data are comparable with those obtainable with sequential shooting using the same number of shot locations. The second example is based on a 3D field test; in which up to 3 fleets of 2 vibrators were swept simultaneously and up to 4 fleets swept with some time overlap. The simultaneous-source data set is coincident with existing data sets acquired with flip-flop and slip-sweep methods in the same area; each requiring significantly more acquisition effort. Migrated images for all three data sets are equivalent; even when no specific attempt is made to remove the interference in the simultaneous-source data set. Separation using sparse inversion is effective in attenuating this interference prestack and is necessary for detailed amplitude analysis. It is envisaged that separation by sparse inversion will become more important as the number of simultaneous sources is increased; or the minimum distance between fleets that sweep simultaneously is decreased.