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Natural Multi-arrival Redatuming of VSP Data to Virtual CDP Data

Natural Multi-arrival Redatuming of VSP Data to Virtual CDP Data. Weiping Cao Feb. 2, 2006. Outline. Motivation Theory and Method Synthetic Example Test on Friendswood RVSP Data Conclusions. Motivation. Good match between geology and VSP reflections;. Less interpretability;.

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Natural Multi-arrival Redatuming of VSP Data to Virtual CDP Data

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  1. Natural Multi-arrival Redatuming of VSP Data to Virtual CDP Data Weiping Cao Feb. 2, 2006

  2. Outline • Motivation • Theory and Method • Synthetic Example • Test on Friendswood RVSP Data • Conclusions

  3. Motivation • Good match between geology and VSP reflections; • Less interpretability; • Wide coverage • Narrow coverage How can we integrate these two to obtain geology and wide coverage? Redatuming VSP data to virtual CDP data

  4. VSP RVSP VSP RVSP ∂G(x|A) ∂G(x|B) G(x|A)] dx G(x|B) ∂nx ∂nx S1 Dipole Approximation VSP RVSP i w ~ ~ cosθ G(x|A) G(x|B)]dx v S1 Monopole Approximation VSP RVSP ~ ~ S1 G(x|A) G(x|B)]dx S1 Theory Green’s Theorem Virtual CDP G(A|B) = [ Free surface A B x S2

  5. B A B A x x VSP G(x|B) G(x|A) CDP G(A|B) VSP VSP Virtual CDP VSP G(A|B) = G(x|B) dx G(x|A) S1 Monopole Redatuming

  6. Advantages of Natural Redatuming • It is a natural redatuming scheme. No velocity model is needed. • We get multi arrivals through redatuming.

  7. Redatum FD Virtual CDP VSP FD True CDP Synthetic Example The velocity model 2800 0 Z (m) 2000 5000 1500 0 X (m) m/s

  8. Receiver depth (m) 0 2000 0 Time (s) 4.0 A VSP gather: the shot at (4000 m, 0 m) Synthetic VSP Data with FD

  9. A true CDP gather A virtual CDP gather X (m) 1520 5000 X (m) 0 5000 1520 0 Time (s) Time (s) 4.0 4.0 Virtual shot position: (780 m, 0 m) Shot position: (780 m, 0 m) Virtual CDP gather vs. True CDP gather

  10. Mismatch 1.0 0.1 Amplitude Artifact -0.6 -0.1 2.8 2.25 2.7 1.9 Time (s) Time (s) Virtual CDP Trace vs. True CDP trace

  11. Reasons for the Artifacts: The monopole approximation and VSP acquisition geometry X (m) 5000 1520 0 Time (s) 4.0 Scattering point A redatumed CDP gather

  12. Dense receiver redatuming result Sparser receiver redatuming result X (m) X (m) 1520 5000 1520 5000 0 0 Time (s) Time (s) 4.0 4.0 Receiver spacing 30 meters Receiver spacing 10 meters The Effect of Spatial Sampling Rate in the Well

  13. A typical common receiver gather Shot Depth (m) 10 300 0 Time (s) 1.0 Test with Real Data Exxon’s Friendswood RVSP data RVSP acquisition geometry

  14. Real VSP gather Virtual CDP gather 0 0 Virtual CDP shot at (-8, 0) RVSP shot at (0, 9) Time (s) Time (s) 1.0 1.0 0 0 183 183 X (m) X (m) Virtual CDP Gather vs. Real VSP Gather

  15. Virtual CDP Trace (lower) vs. Real Trace (upper) 0.1 -0.1 Normalized Amplitude 0.5 -0.5 0 0.7 Time (s)

  16. Conclusions • Tests with both synthetic and real data indicate the validity and feasibility of this VSP to CDP redatuming scheme. • Artifacts are due to limited discrete spatial sampling,monopole approximation to the Green’s Theorem, and other possible reasons. • This scheme is also promising for transforming OceanBottom Seismic (OBS) data to marine CDP data.

  17. Acknowledgements We thank the 2005 UTAM sponsors for the support of the research.

  18. Thanks

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