a


b


c


d


Figure 5.57: Amplitude spectra of seismic data acquired using various acquisition systems: (a) conventional streamer (2007); (b) OBC data (2008); (c) GeoStreamer (2009); and (d) BroadSeis/BroadSource (2012).


it is crucial to fill the gap between stacking velocities, well log data and seismic data. At the Utsira High both these challenges are important,


and early in the exploration phase Lundin’s geophysicists embarked on a project aimed at understanding how these frontiers (low and high frequency content) could be met and actually measured and controlled. Tere are several challenges related to establishing a field laboratory like this. First of all, the technology is rapidly expanding and therefore it will never be fair to compare the results obtained by one contractor with those obtained by another contractor two years later. Furthermore, different contractors have different processing algorithms, causing different end results when the same data is used as input. Finally, weather conditions will always change between various acquisitions. Despite this, the main conclusion is clear-cut: broadband


seismic data is better than old conventional data. Tis is demonstrated in Figure 5.57, where amplitude spectra from four types of acquisition are compared for the same 2D line at the Utsira High area. Another example illustrating the progress in broadband


seismic is shown in Figure 5.59, where we can observe distinct improvements in seismic imaging from 1995 to 2009 and finally 2012. We notice especially that the imaging of top basement (the lowermost clear reflector seen on these images) is significantly improved from 1995 to 2012.


5.9.2 Testing Streamer Configurations


In 2013 Lundin initiated a huge practical experiment to be conducted at the Utsira High. Together with a seismic contractor, they tested 11 different streamer configurations at the same time. Te same 2D line was shot over and over again using the same source configuration but with different shapes of the streamer (Figure 5.60). Maybe the most spectacular (and the most difficult for the contractor to achieve) was the ‘snake’ configuration, where the streamer has a sinusoidal shape


a b


Figure 5.58: The Utsira High area, including the giant Johan Sverdrup field, Edvard Grieg field and the Luno II field.


varying from 15 to 35m. Tis extensive experiment gives a unique insight into how various towing configurations might impact the final imaging result. A comparison between the snake configuration and a conventional streamer towed at 8m depth is shown in Figure 5.61, and it is actually hard to spot any major differences. A clear difference is observed, however, when the low


Figure 5.59: Conventional streamer data from 1995 (a), GeoStreamer data from 2009 (b) and BroadSeis data from 2012 (c). c


Edvard Grieg


Johan Sverdrup


Luno II


229


Lundin


Lundin


Lundin


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