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Kui Zhang* and Kurt J. Marfurt

Migration-driven velocity analysis for anisotropy/stress analysis. Kui Zhang* and Kurt J. Marfurt. 2008 AASPI Consortium annual meeting. Motivation. Our industry is acquiring more and more wide azimuth data.

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Kui Zhang* and Kurt J. Marfurt

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  1. Migration-driven velocity analysis for anisotropy/stress analysis Kui Zhang* and Kurt J. Marfurt 2008 AASPI Consortium annual meeting

  2. Motivation • Our industry is acquiring more and more wide azimuth data. • Traditional seismic processing often ignores the azimuth information and implements on the full azimuth gathers. • The presence of azimuthal velocity anisotropy can degrade image quality. • The analysis of azimuthal velocity anisotropy and/or azimuthal AVO provides valuable information about fracture densities and stress orientation. Current leaders are: • Axis (NMO-based), • Weinman (migration-based).

  3. Motivation • Challenges: • Statics caused by different elevations and the LVL zone.(short wavelength and long wavelength) • Structural dip can bias the anisotropic analysis. • Measured elliptical NMO velocities is usually converted to interval velocity by Dix equation. (ambiguity) • We use Kirchhoff prestack migration-driven approach to generate: • More accurate NMO azimuthal velocities • High resolution imaging

  4. N 349° 11° 34° 326° 56° 304° 79° 281° E 1 1 7 6 6 5 5 7 4 3 8 3 4 2 2 8 W 259° 101° 236° 124° 146° 214° 191° 169° S New azimuth binning method Vfast Vslow (xi-xs)+ (xi-xg) xi (xi-xs) (xi-xg) xs Fault plane xg

  5. N 1 2 Amplitude 3 4 Positive 0 5 6 Negative 1 km 7 8 Conventional Binning

  6. N 1 2 Amplitude Positive 3 4 0 Negative 5 6 1 km 7 8 New Binning (Perez and Marfurt, 2008)

  7. New P wave azimuthal velocity analysis approach NMO velocity Vnmo Coarse grid selection Maximum semblance Choose α and φ V=Vnmo+ α cosφ +10% Migrate and compute semblance α more α or φ Yes 0% 180 0 0 1 Scan for maximum semblance over αm and φm migrate over αm and φm

  8. New converted wave azimuthal velocity analysis approach P S For P wave migration: P P t=0 For PS wave migration: t2s=(t02+xgi2/vs2)1/2 t1p=(t02+xsi2/vp2)1/2 t2p=(t02+xgi2/vp2)1/2 Maximum semblance Vs/Vp

  9. Acknowledgement We thank all sponsors of AASPI consortium for their support.

  10. Thank you!

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