Transcript Title, 24pt Arial Bold - University of Houston

Three VSP Algorithms: Surface Seismic
Transform, NMO and Migration
Velocity Analyses
Yue Du
Mark Willis, Robert Stewart
AGL Research Day
April 2nd, 2014
Houston, TX
© 2011 HALLIBURTON. ALL RIGHTS RESERVED.
1
Talk outline
• Motivation & introduction
VSP has higher resolution, target oriented, small data volume
• Three algorithms
1. Transforming VSP to surface seismic data;
2. Downward continuation of surface shots with joint NMO velocity analysis;
3. Residual moveout migration velocity analysis
• Future work
-Hess VSP survey
2
1. Transforming VSP to surface seismic records
G(B | A) 
kG(x | A)G(x | B )dx

Swell
(Schuster , 2009)
Part 1
G(B | A) 
k  G(x | B )upreflecti ons G(x | A)firstarriv als

Swell
Part 2
 G(x | B )firstarriv als G(x | A)upreflecti ons dx
3
Two-layer model simulation results
Surface seismic shots
Simulating shot from VSP
1
1.5
1.5
2
2
time,s
time,s
1
2.5
2.5
3
3
3.5
0
500
1000
1500
offset,m
2000
2500
3.5
3000
0
500
1000
1500
offset,m
2000
2500
3000
Simulating shot from VSP with taper Reduced receiver coverage
1
1.5
1.5
2
2
2.Seprate waveform
convolution— without
first arrivals
time,s
time,s
1
2.5
2.5
3
3
3.5
0
500
1000
1500
offset,m
2000
2500
3000
3.5
1.2D acoustic finite
difference modeling
3.Artifacts—taper
0
500
1000
1500
offset,m
2000
2500
3000
4.Borehole receiver
coverage
4
2D & 3D simulation results
Left – Actual surface shot
Middle – simulated surface shot from
the Part 1
Right – simulated shot from Part 2
5
2. Downward continuation with joint NMO analysis
1
Reflector A
2
Reflector B
6
Downward continuation
• Downward continued data
• Raw data
receiver 1
receiver 1
0
0
Reflection A
Reflection A
1
travel time (s)
travel time (s)
0.5
1.5
2
Reflection B
2.5
0.5
Reflection B
1
3
3.5
-6000
-4000
-2000
0
2000
4000
1.5
6000
0
100
200
300
400
500
600
700
800
900
1000
900
1000
receiver 2
receiver 2
0
0
1
travel time (s)
travel time (s)
0.5
1.5
Reflection B
2
2.5
0.5
Reflection B
1
3
3.5
-6000
-4000
-2000
0
source receiver offset
2000
4000
6000
1.5
0
100
200
300
400
500
600
source receiver offset
700
800
7
NMO correction and semblance spectra analysis
• Before NMO correction
• After NMO correction
Traces before NMO correction
Traces after NMO correction
0
0
0.1
Reflection A
0.2
Reflection A
0.3
Reflection B
zero offset time (s)
zero offset time (s)
0.5
Reflection B
0.4
0.5
0.6
Reflection B
Reflection B
1
0.7
0.8
0.9
Receiver 2
10
20
30
Receiver 2
40
traces
50
60
70
80
1
10
20
30
Receiver 1
t 
2
V Rms

t 
2
0
4b 2
2
V Rms
V bot 
2
Vtop
50
2z
tbot  ttop 
4b 2  4z 2
Receiver 1
40
traces
2
ttop
2
 V rms z

70
80
velocity spectrum for all receivers
V rms
ttop
60
0
z
V rms
zero-offset time (s)
1.5
1
0.1
0.9
0.2
0.8
0.3
0.7
0.4
0.6
0.5
0.5
0.6
0.4
0.7
0.3
0.8
0.2
0.9
1
1800
0.1
2000
2200
2400
velocity (m/s)
2600
2800
3000
0
8
3. Migration velocity analysis
VSP Model Reflector Depth = 2700, Vtrue = 2500, Vmig =2500
-2000
XOZ coordinates
V
migrated image
depth
m
depth,
migration
-1000
0
s
source
δ
O’
1000
X
O
g
receiver
Tilted ellipse
coordinates UO’V’
U
2000
Reflector
3000
4000
-6000
CIP
-5000
-4000
-3000
-2000
-1000
source offset
Z
0
XOZ coordinates
1000
2000
3000
4000
X,
x m
9
The intersections of tilted migration ellipses
Correct velocity
500
depth, m
migration depth
0
Slow velocity
source3
Receiver
2000
z3
z1
3000
-6000 -5000 -4000 -3000 -2000 -1000
1500
2000
z2
0
1000 2000 3000 4000 5000
x X, m
Slow velocity
0
Correct velocity
2500
3000
-8000
source2
1000
-6000
-4000
-2000
0
2000
source x
4000
Source X, m
6000
8000
migration
mdepth
depth,
migration depth
migration depth, m
1000
source1
source1
source2
1000
2000
z1
3000
-6000 -5000 -4000 -3000 -2000 -1000
source3
z3
Receiver
zz1
2
0
x X,
1000 2000 3000 4000 5000
m
10
Residual moveout after migration
RMO for a CIG
Unstacked CIG
2100
2100
2200
Slow velocity
2300
2300
2400
2400
2500
2500
2600
Correct velocity
2700
2800
CIG extreme m
point depth
depth,
Depth, m
migrated image depth
2200
2600
2700
2800
2900
2900
3000
3000
Fast velocity
3100
3200
-8000
-6000
-4000
-2000
0
2000
source offset
source
Source
X,xm
4000
6000
8000
3100
3200
1000
1200
1400
1600
1800
2000
depth
recvier depth,
receiver
m
11
VSP multi-layer model
0
Modeling data with
reflection events only
Receiver gather R1
time, ms
1000
0
2000
Shot gather for source x=0
time, ms
1000
3000
2000
3000
4000
Receiver depth
Source offset
12
Downward continuation with joint NMO analysis
• Pick RMS velocity
• Interval velocity model
VSP multi-layers velocity Model
0
500
True
velocity
model
1000
1500
N
1
N

k
 k
depth
V Rms 
 kV k

k
2
2000
Estimated
velocity
model
1
2500
3000
3500
4000
2000
2500
velocity
3000
13
Migration velocity analysis
VSPVelocity
multi-layers Model
velocity Model
0
Tilted Ellipse
RMOs
Layer 4
RMO After Migration
Vmig = Vtrue
2600
2600
2620
500
A (Vlayer4=0.9Vtrue)
2640
1000
2660
2000
2500
2680
2700
Depth, m
Depth, m
CIG extreme point depth
depth
1500
A’ (Vlayer4=0.95Vtrue)
B (Vlayer4=Vtrue)
2720
2700
C (Vlayer4=1.05Vtrue)
2740
3000
2760
3500
C’ (Vlayer4=1.1Vtrue)
2780
4000
2000
2500 3000
velocity
Velocity,
m/s
2800
1000
2800
1500
receiver depth
2000
Receiver Depth, m
Receiver Depth
15
Summary
• VSP geometry is asymmetric, thus it is hard to apply
velocity analysis tools from surface seismic
• The three algorithms can be used separately or together
to help VSP analyses
• Transforming to surface seismic records from VSP data
has limitations
16
Acknowledgements
• Allied Geophysical Lab and its supporters
• Halliburton
• Thank you kindly Michele Simon and colleagues at Hess for
contributing the 3D time-lapse Bakken data for our future
research. We also express our appreciation to Richard Van Dok
at Sigma3 for data preparation.
17