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Acquisition of long-offset data offshore Gabon shows how synchronized source technology adds flexibility to tailored acquisition solutionsNormal access

Authors: Thomas Mensch, Krzysztof Cichy, Risto Siliqi, Jo Firth and Benoit Jupinet
Journal name: First Break
Issue: Vol 34, No 11, November 2016 pp. 95 - 101
DOI: EAGE-EXPORT-FAKE-DOI
Language: English
Info: Article, PDF ( 1.8Mb )
Price: € 30

Summary:
The current climate in the oil exploration industry has engendered a strong push towards efficiency in acquisition. One technique that offers this is synchronized sources, or SyncSource, where sources are activated before the recording of data from the previous shot has been completed. As this may result in significant overlap of seismic data between successive shot records, it means that the data must be de-blended to recover the individual contribution from each source. However, this makes it possible to acquire data with higher trace density, smaller bins or longer records than can be achieved using conventional acquisition techniques. The simultaneous shooting technique has been commonly used in land acquisition for some years and its potential for ocean bottom and towed-streamer acquisition has been well documented (e.g. Moore et al., 2012; Davies et al., 2013; Poole et al., 2014). As long as the de-blending can be performed successfully, without compromising the data quality, there are many advantages to synchronized source acquisition in terms of quality and efficiency, based on the fact that the sources can be activated more frequently. This offers options for new acquisition geometries that had previously been either impossible or prohibitively expensive. It becomes possible to maximize efficiency either by increasing vessel speed without increasing shotpoint interval or reducing record length, or by reducing crossline bin spacing by adding a source rather than by reducing cable separation. Superior resolution can be achieved with a finer shot grid and a higher trace density to deliver higher-fold images with better signal-to-noise ratio and smaller bin size. Better illumination at depth can be achieved by increasing the recording time with the optimal source-receiver offset and azimuth, through the deployment of additional source vessels, without compromising the shot density or acquisition time. Recent advances in acquisition equipment and technology have combined with advances in de-blending and cross-talk attenuation algorithms in processing to allow blended acquisition offshore to become a realistic option. We have successfully conducted a full-scale commercial survey of 2500 km2 using this technology in order to acquire ultra-long offset data offshore Gabon. In Gabon’s South Basin, the geology is very complex with both pre- and post-salt plays, while compressional zones and salt basins cause challenges for illumination and imaging. This area is in a continental passive margin and exhibits the classic characteristics of a gravity-driven collapse system (Figure 1). Upslope, there is a broad region of extension, with normal faulting, rollover anticlines, thin salt with pillows and carbonate rafts. Downslope, there is a compressional domain with thrust faulting, folds, tilted diapirs and complex extruded salt structures. In between there is a transitional zone of upright diapirs and local welds (Xiao et al., 2016).


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