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

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).

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

New azimuth binning method V fast V slow Fault plane xixi xsxs xgxg (x i -x s)+ (x i -x g ) (x i -x s) (x i -x g ) 11° 34° 56° 79° 101° 124° 146° 281° 304° 326° 349° E W N 169°191° 214° 236° 259° S

1 km Amplitude Positive Negative 0 N Conventional Binning

km Amplitude Positive Negative 0 N New Binning (Perez and Marfurt, 2008)

New P wave azimuthal velocity analysis approach Coarse grid selectionNMO velocity V nmo Choose α and φ V=V nmo + α cosφ Migrate and compute semblance more α or φ Yes Scan for maximum semblance over α m and φ m migrate over α m and φ m α +10% 0% Maximum semblance

New converted wave azimuthal velocity analysis approach t 1 p =(t 0 2 +x si 2 /v p 2 ) 1/2 t 2 p =(t 0 2 +x gi 2 /v p 2 ) 1/2 t 2 s =(t 0 2 +x gi 2 /v s 2 ) 1/2 t=0 P P S For P wave migration: For PS wave migration: Vs/Vp Maximum semblance

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