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1 © 2011 HALLIBURTON. ALL RIGHTS RESERVED.
VSP modeling, velocity analysis, and imaging in complex structures
Yue DuWith
Mark Willis, Robert Stewart
May. 16th, 2013
Houston, TX
Work Outline
• 1. Introduction to Vertical seismic Profile(VSP);
• 2. VSP modeling investigation;
• 3. Velocity model building and imaging.
2
Why Vertical Seismic Profiling (VSP)?
3
High-resolution imaging example
Representation of a 3D VSP imaging survey.
(Hornby et al., 2006)
Gulf of Mexico Velocity Model
Coordinates: X: 0-10025 m Y: 0-10025 m Z: 0-8000 m
Grid no.: 402*402*1601
Grid Spacing: 25m*25m*5m
Example for a 2D plane
4
Carbonate
Carbonate
Siliciclastic series
limestone
limestone
shales
Carbonate
Siliciclastic series
(Hallliburton/Pemex)
Shots
Receivers
Ray Tracing(RT) model for far-offset (i.e. 13th shot)
5
Ray Tracing(RT) modeling results
1st. Rec. gather
Acoustic FD modeling results:
6
1st. Rec. gather
SeisSpace acoustic FD modeling RT modeling
Comparison between FD and RT modeling
7
Comparison between acoustic and elastic FD modeling:
8
Fist break
Shear wave?
SeisSpace acoustic FD modeling
9
Imaging results comparison between SeisSpace acoustic FD modeling and RT modeling Data
RT modeling Receiver
Kirchhoff Migration results: 20% slow velocity_v/1.2
10
Northings, m
De
pth
, m
2.145 2.146 2.147 2.148 2.149 2.15 2.151 2.152 2.153 2.154
x 106
0
1000
2000
3000
4000
5000
Kirchhoff Migration results: correct velocity_v
Northings, m
De
pth
, m
2.145 2.146 2.147 2.148 2.149 2.15 2.151 2.152 2.153 2.154
x 106
0
1000
2000
3000
4000
5000
Kirchhoff Migration results: 5% fast velocity_v/0.95
Northings, m
De
pth
, m
2.145 2.146 2.147 2.148 2.149 2.15 2.151 2.152 2.153 2.154
x 106
0
1000
2000
3000
4000
5000
Kirchhoff Migration results: 20% fast velocity_v/0.8
Northings, m
De
pth
, m
2.145 2.146 2.147 2.148 2.149 2.15 2.151 2.152 2.153 2.154
x 106
0
1000
2000
3000
4000
5000
s
0bb
R
2R
0
gz - g
z
s - bb bb
Setting tsig to tsg can get migration in a CIG(bb)
For this shot and receiver pair, the arrival time of the actual reflection (LHS of equation), will have to match the “migration time” where it is put in the migrated image (RHS of equation).
Migration Equation:
sigm
sg tv
zbbsbbgzv
sgRt
222222 )()()2(
11
Geometry for Migration in a CIG gather
Methodology: Tilted Ellipse
12
2
2
2
b
v
a
u
cosau sinbv Tvmiga *2
222 gsc
In UO’V coordinates:
mkuv
gs
ctgk
222 gsg
bs
m
Intersection: 222
22222
kabkabmabkma
u
mkuv ,
12
The intersections of the tilted migration ellipses
13
Diagram showing the intersections of the tilted migration ellipses with a CIG. (a) For the migration velocity equal to the true velocity (2500m/s). (b) For a slower migration velocity (2000m/s)
Wrong Migration Velocity Pulls in the Wrong Data
14
Numerical examples for residual moveout in a single receiver offset with a CIG (bb=-500m). (a) For the migration velocity equal to the true velocity (2500m/s). (b) For a slower migration velocity (2000m/s). The red curve is the solution to the MI equation. The extreme point will be the depth of migrated reflector.
Residual moveout after migration for a numerical example
15
(a) Residual moveout in the migrated, unstacked trace domain, M(s, g, z). (b) The residual moveout in a migrated, stacked trace domain, M(g, z), derived from the black stationary phase points in panel a.
VSP multi-layer model
16
Residual moveout for layer 4 comparing with the migration results
17
1000 1500 2000
2600
2620
2640
2660
2680
2700
2720
2740
2760
2780
2800
receiver depth
CIG
ext
rem
e po
int
dept
h
Layer 4
A (Vlayer4=0.9Vtrue)
A’ (Vlayer4=0.95Vtrue)
B (Vlayer4=Vtrue)
C (Vlayer4=1.05Vtrue)
C’ (Vlayer4=1.1Vtrue)
Residual moveout for layer 4 in the multi-layer velocity model.
Migration results with changing interval velocity for layer 4 in case A and C’.
Acknowledgements
• Thank you for Dr. Rob Stewart and AGL friends for the support and guidance in my Ph.D. studies
• Thank you for Dr. Mark Willis and colleagues at Halliburton
18
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