Signal apparition applied to towed marine simultaneous sources – a case study on synthesized real data from the Viking Graben

Abstract

Encoding sources using random dithers for simultaneous source acquisition offers significant scope for enhanced towed marine operations. However, so far it has proven to be challenging to reduce the decoding residual noise from these techniques to a level that is widely accepted by the industry. The emerging technology of signal apparition offers a new approach to overcome this challenge. In contrast to established thinking, the signal apparition concept capitalizes on periodic rather than random shot-to-shot modulation functions to facilitate shot separation. The approach allows us to efficiently populate the available data space in, for instance, the frequency wavenumber domain with energy from different simultaneous sources. The introduction of periodic modulation functions in seismic acquisition produces an effect where parts of the energy of one or more sources are shifted to different empty parts within the frequency wavenumber (f-k) domain. This so-called apparated energy can then be used to perfectly predict at low frequencies the remaining part of the signal in the regions of the f-k domain where the wavefields from the different sources overlap and to deterministically separate the sources. On a synthesized real data set from the Viking Graben in the North Sea, the suitability of this concept to marine seismic simultaneous sources is demonstrated. An operational scenario for a single vessel is designed where the source arrays are excited simultaneously. Having two closely spaced simultaneous sources is a challenging case for shot separation but, if successful, such a cost-effective single-vessel configuration offers highly significant productivity gains. The wavefield decoding results analysed pre-stack and post-stack are very encouraging and indicate that the signal apparition concept indeed has the potential to deliver the high quality source decoding required for many seismic applications.