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Using Dual Azimuth Acquisition to Illuminate Beneath Salt Domes

Using Dual Azimuth Acquisition to Illuminate Beneath Salt Domes. Fiona Dewey 1 Julia Bernard 2 1 Wintershall Noordzee BV 2 Now with Wintershall Erdoelwerke A.G. Agenda. The Problem Acquisition Time Processing Depth Migration Results Conclusions Acknowledgements. ?. ?.

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Using Dual Azimuth Acquisition to Illuminate Beneath Salt Domes

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  1. Using Dual Azimuth Acquisition to Illuminate Beneath Salt Domes Fiona Dewey 1 Julia Bernard 2 1 Wintershall Noordzee BV 2 Now with Wintershall Erdoelwerke A.G.

  2. Agenda • The Problem • Acquisition • Time Processing • Depth Migration • Results • Conclusions • Acknowledgements

  3. ? ? The ProblemPoor Imaging Below Salt Structures W E 1990 Acquisition with (1999) PrSDM processing

  4. The Problem Many gas discoveries close to salt features.

  5. The Solution New Acquisition • Determine best acquisition direction for illumination • Optimize streamer length Improved Processing Techniques • Improved noise suppression • Prestack Depth migration taking anisotropy into account

  6. Dip vs Strike Acquisition Industry rules: Dip Shooting • Better imaging below complex overburden Strike shooting • Better at imaging salt flanks • Multiple energy more coherent

  7. Illumination Study Study Objectives: • Map illumination for different acquisition directions • Investigate effect of increasing cable length

  8. Illumination Study Conclusions: • Illumination patchy under salt ridge • N-S acquisition provides additional illumination under salt flanks • Optimal cable length 5000-6000 m

  9. Acquisition Parameters Comparison

  10. 2003 Acquisition Program Main acquisition direction W-E (556 km²) Two additional swaths N-S (196 +185 km²)

  11. Hide Vessel Position Tracks Shooting pattern optimised to reduce waiting on tides and maximise feather matching

  12. Conclusions • Illumination differences seen on sides and under salt structures • Away from salt illumination differences are small • In less complex areas summation of PrSTM data sets gives improved signal to noise • Depth migration moves steep dips to similar locations • Anisotropy parameters defined for each orientation

  13. Summary • Orthogonal acquisition combined with long streamers has illuminated previously hidden parts of the subsurface • Challenges still remain in processing to define one unique velocity field that will account for the differences in anisotropy of the two acquisition directions • Does the imaging improvements justify the extra cost ??

  14. Working Together

  15. Acknowledgement Wintershall Noordzee BV Energie Beheer Nederland BV Petro-Canada

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