1. 1 AVO INVERSION OF LONG-OFFSET SYNTHETIC PP DATA BASED ON EFFECTIVE REFLECTION COEFFICIENTS 10 April 2008 Lyubov Skopintseva Milana Ayzenberg, Martin Landrø Tatyana Nefedkina, Arkady Aizenberg

2. AVO-analysis. What is that? Conventional AVO analysis: Range of incidence angles: 0-40 0 Weak contrasts at reflector

3. Pre-critical region Critical angle Post-critical region Plane-wave reflection coefficient

4. Effective reflection coefficient (ERC) Incident wave Plane-wave decomposition Division by incident wave Multiplying by plane- wave reflection coefficient (PWRC) Summation

5. ERC versus PWRC PWRC valid for plane waves ERC generalize PWRC for point sources - incidence angle - frequency - wavefront curvature - wave velocity

6. ERC versus PWRC

7. Model parameters

8. Z-component from reflectivity modeling

9. AVO response

10. Spectrogram

11. AVO response comparison with ERC and PWRC

12. Plane-wave reflection coefficient Effective reflection coefficient Cost functions comparison (pre-critical offsets)

13. Cost functions comparison (all offsets) Effective reflection coefficient Plane-wave reflection coefficient

14. AVO inversion results ERC solutionPWRC solution

15. 15 Conclusion ERC give better estimates than PWRC Rapid variations in reflection amplitude for post-critical offsets improve inversion results Long-offset data allow accurate estimation of Vp and Vs