Post on 13-Jan-2016
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
Vfast
Vslow
Fault plane
xi
xs
xg
(xi-xs)+
(xi-x
g)
(xi-xs)
(xi-x
g)
11°34°
56°
79°
101°
124°
146°
281°
304°
326°349°
EW
N
169°191°214°
236°
259°
S
1
1
2
23
34
4
556
67
78
8
1 km
1 2
3 4
5 6
7 8
Amplitude
Positive
Negative
0
N
ConventionalBinning
1 2
3 4
5 6
7 8
1 km
Amplitude
Positive
Negative
0
N
NewBinning
(Perez and Marfurt, 2008)
New P wave azimuthal velocity analysis approach
Coarse grid selectionNMO velocity Vnmo
Choose α and φV=Vnmo+ α cosφ
Migrate and compute
semblance
more α or φ
Yes
Scan for maximum semblance over αm and φm
migrate over αm and φm
α
+10%
0%
Maximum semblance
0 180
0 1
New converted wave azimuthal velocity analysis approach
t 1p =(
t 02 +x
si2 /v
p2 )1
/2
t 2p =(t
02 +x gi
2 /v p2 )1
/2
t 2s =(t 0
2 +x gi2 /v s
2 )1/2
t=0P P P S For P wave migration:
For PS wave migration:
gs
Ppsgp ttdm
,21 )(
gs
Spsgs ttdm
,21 )(
Vs/Vp
Maximum semblance
Acknowledgement
We thank all sponsors of AASPI consortium for their support.