PGS Customised HD3D surveys for Shell
Posted: 10 November 2004
PGS seismic vessel M/V Ramform Valiant recently completed three customised HD3D-4D monitor surveys for Shell Exploration and Production in Europe, offshore Norway and UK. All surveys have been acquired using shot point repetition and overlap, a 4D acquisition technique endorsed by PGS.
The seismic survey conducted over A/S Norske Shell’s Draugen field is regarded as a milestone in HD3D-4D acquisition. The M/V Ramform Valiant deployed an overlap configuration with 10 streamers at 37.5m separation in order to repeat a previous survey shot by the PGS M/V Atlantic Explorer in 2001. When the previous survey was acquired, the M/V Atlantic Explorer towed 6 streamers at 75m separation over a 4 streamer pre-plot. Both surveys used dual-source shooting. The 2001 survey resulted in an ideal 4D base survey with overlapping coverage and close to zero infill. The denser streamer separation now deployed by the M/V Ramform Valiant combined with the overlap and the shot point repetition has resulted in an accurate match of source-receiver azimuths, providing superior 4D repeatability. In addition to being a good quality survey, the Draugen HD3D survey is characterised by very dense crossline sampling and a high trace density, ensuring the preservation of the frequency content for high resolution imaging and a good S/N ratio, respectively.
The M/V Ram form Valiant also acquired 4D monitor surveys at Shell U.K. Limited’s Shearwater and Gannet fields. In both cases the PGS vessel deployed 10 streamers at 100m separation over eight streamer pre-plot surveys. The corresponding base surveys have been acquired using the same overlap configurations. The overlap minimises infill shooting and results in oversampling of the surface fold at sail line boundaries, making it possible to use selective 4D binning schemes in processing in order to maximise repeatability.
Posted by Alexander Lindsay, Editor Pipeline Magazine
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