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Separation and Imaging of Water-layer Multiples for Walk-away VSP Surveys
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 77th EAGE Conference and Exhibition 2015, Jun 2015, Volume 2015, p.1 - 5
Abstract
Walk-away VSP surveys allow to obtain information about the subsurface structure thanks to the multi-component geophones in the borehole that record the pressure field originating from a seismic source at the surface and reflected by interfaces in the subsurface. Different spurious wavefields can contaminate reflection data: among them, multiple arrivals can be the most energetic source of coherent noise that can hide information recorded at target level for marine acquisitions, especially in shallow water environments. Fully data-driven multiple elimination techniques cannot be directly applied to VSP datasets, because of the lack of recordings at surface level. However, the knowledge of the bathymetry allows to model and subtract water-layer multiples, at least.
Thus, a procedure to estimate, subtract and separate by order water-layer multiples is described. Furthermore, an iterative schema is proposed to separate by order and then correctly depth–migrate the estimated water-layer multiple reflections.
A so-called “double-mirror” imaging approach is derived, that relies on a simple source geometry modification: imaging of multiples can be performed without the need of any modification of standard depth-migration tools. Results on simulated data prove the feasibility of the proposed approach.