a set of streamers and some offset ranges along a number of streamers for a number of sail lines. In addition to the full data set S1, the data
output coverage colour plots for each target horizon and for a selected set of offset ranges. An example of the Far Offset FZB coverage for the S3 data scenario is shown in Fig. 2.
capable of handling multiple and conflicting dips.
High quality processing algorithms for
wave field reconstruction and regularisation are today available in the seismic processing industry.
A number of time slices of the S2 and S3 data sets were generated and analysed for different offset planes. Data holes and amplitude stripes are clearly visible in the data. All offset planes are interpolated and the data finally prepared for 3D Kirchhoff time migration. Data quality comparison and difference analysis has been done on a set of time slices, in- and cross-line sections for the three alternative data sets.
decimation simulated two additional data sets S2 and S3. Te S2 data were decimated down to -2 to -3dB and the S3 data further decimated down to -3 to -4dB. Te three independent data sets were processed independently and used for comparison and data quality analysis.
FZB infill analysis Te FZB calculations are performed for all shot and receiver combinations along all the sail lines. A subsurface model of the survey area is
defined and used in the FZB calculations, consisting of target horizons, an overburden macro velocity model and estimated seismic bandwidth. Te output from FZB is a set of
Fig. 2. Note that the lowest dB levels for the
FZB coverage (-3dB to -4dB) are located at the light coloured areas in the figure. Te question is whether the FZB dB threshold used (S3) is conservative enough to generate high quality imaging of the subsurface
Data processing / interpolation Te three data sets were all subject to the same processing flow prior to the final 3D Kirchhoff time migration, including the regularisation step. Te Fresnel zones or data holes may be large for deeper targets and larger offsets and it is therefore essential that prior to pre-stack migration, the offset data are accurately interpolated with advanced algorithms
Conclusion Te FZB processing tests performed on the Nordkapp data have demonstrated that the infill requirements based on Fresnel Zone criteria have proved to be appropriate in order to obtain high quality output images after 3D pre-stack time migration. Te most severe data decimation (S3) has
simulated coverage which is -3 to -4 dB down from a theoretical coverage of one. Although with relative large holes in the Nominal Fold for the far offsets, the lack of coverage can be accommodated if FZB sampling criteria are used and high fidelity regularization/ interpolation is performed.
Enter 13 or ✔ at www.engineerlive.com/ihss
Hejie Wang, Usman Raja, Jingdong Liu and Ottar
Sandvin are with with Fugro Seismic Imaging, Oslo, Norway. www.fugro.no
Acknowledgements: We would like to thank Statoil and its partner GdF Suez E&P Norge, for access to seismic data and authorization to show the obtained results, and Fugro for permission to present this work.
Monk, D J, 2010, Reducing infill requirements using Fresnel zone binning and Steerable streamers. SEG Denver 2010 Annual Meeting; Monk, D J, 2010, Fresnel zone binning: Fresnel- zone shape with offset and velocity:
Geophysics, 75, no.1, T9-T14; Monk, D J, 2010, Fresnel zone binning: Application to 3D seismic fold and coverage assessment, Leading Edge; Young P and Monk D J 2010, Alternative coverage analysis method reduces infill Shooting. World Oil Magazine, September 2010.
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