1 © 2011 HALLIBURTON. ALL RIGHTS RESERVED. 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
Dec 18, 2015
1 © 2011 HALLIBURTON. ALL RIGHTS RESERVED.
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
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
3
Swell
dxBxGAxkGABG )|()|()|(
(Schuster , 2009)
Swell
alsfirstarrivonsupreflecti AxGBxGkABG )|()|()|(
dxAxGBxG onsupreflectialsfirstarriv )|()|(
Part 1
Part 2
offset,m
time,
s
0 500 1000 1500 2000 2500 3000
1
1.5
2
2.5
3
3.5
offset,m
time,
s
0 500 1000 1500 2000 2500 3000
1
1.5
2
2.5
3
3.5
Two-layer model simulation results
4
Simulating shot from VSP with taper Reduced receiver coverage1.2D acoustic finite difference modeling
2.Seprate waveform convolution— without first arrivals
3.Artifacts—taper
4.Borehole receiver coverage
offset,m
time,
s
0 500 1000 1500 2000 2500 3000
1
1.5
2
2.5
3
3.5
Simulating shot from VSP
offset,m
time,
s
0 500 1000 1500 2000 2500 3000
1
1.5
2
2.5
3
3.5
Surface seismic shots
2D & 3D simulation results
5
Left – Actual surface shot
Middle – simulated surface shot from the Part 1
Right – simulated shot from Part 2
receiver 1
trav
el t
ime
(s)
-6000 -4000 -2000 0 2000 4000 6000
0
0.5
1
1.5
2
2.5
3
3.5
receiver 2
trav
el t
ime
(s)
source receiver offset-6000 -4000 -2000 0 2000 4000 6000
0
0.5
1
1.5
2
2.5
3
3.5
receiver 1
trav
el t
ime
(s)
0 100 200 300 400 500 600 700 800 900 1000
0
0.5
1
1.5
receiver 2
trav
el t
ime
(s)
source receiver offset0 100 200 300 400 500 600 700 800 900 1000
0
0.5
1
1.5
Downward continuation
• Raw data • Downward continued data
Reflection B
Reflection A
Reflection B
Reflection B
Reflection B
Reflection A
7
traces
zero
off
set
time
(s)
Traces after NMO correction
10 20 30 40 50 60 70 80
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
traces
zero
off
set
time
(s)
Traces before NMO correction
10 20 30 40 50 60 70 80
0
0.5
1
1.5
NMO correction and semblance spectra analysis
• Before NMO correction • After NMO correction
Receiver 1Receiver 2
Receiver 2 Receiver 1
2
2202
22 444
RmsRms V
bt
V
zbt
rms
top
rmstop
top
bot
Vzt
zVt
VV
2
22
rmstopbot V
ztt
2
Reflection A
Reflection B
Reflection A
Reflection BReflection B
Reflection B
velocity spectrum for all receivers
velocity (m/s)
zero
-off
set
time
(s)
1800 2000 2200 2400 2600 2800 3000
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
8
-6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000
-2000
-1000
0
1000
2000
3000
4000
source offset
mig
rate
d im
age
dept
h
VSP Model Reflector Depth = 2700, Vtrue = 2500, Vmig =2500
XOZ coordinates
Tilted ellipse coordinates UO’V’
3. Migration velocity analysis
gO’
s
V
source
receiver
Reflector
CIP
XO
U
Z
δ
xX, m
XOZ coordinates
9
-8000 -6000 -4000 -2000 0 2000 4000 6000 8000
500
1000
1500
2000
2500
3000
source x
mig
rati
on
dep
th
-6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000
0
1000
2000
3000
x
mig
ratio
n de
pth
-6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000
0
1000
2000
3000
xm
igra
tion
dept
h
The intersections of tilted migration ellipses
source1 source2 source3
source1 source2 source3
1z
1z2z3z
2z
3zReceiver
Receiver
Slow velocity
Correct velocity
Slow velocity
Correct velocity
X, m
X, m
Source X, m
1z
10
receiver depth, m
Residual moveout after migrationUnstacked CIG RMO for a CIG
1000 1200 1400 1600 1800 2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
recvier depthC
IG e
xtr
em
e p
oin
t depth
-8000 -6000 -4000 -2000 0 2000 4000 6000 8000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
source offset
mig
rate
d im
age d
epth
Slow velocity
Correct velocity
Fast velocity
source xSource X, m
11
Shot gather for source x=0
Receiver depth
0
1000
2000
3000
VSP multi-layer modelModeling data with
reflection events only
Receiver gather R1
Source offset
0
1000
2000
3000
4000
12
Downward continuation with joint NMO analysis
• Pick RMS velocity • Interval velocity model
N
kk
k
N
kk
Rms
VV
1
2
1
2000 2500 3000
0
500
1000
1500
2000
2500
3000
3500
4000
velocity
dept
h
VSP multi-layers velocity Model
True velocity model
Estimated velocity model
13
2000 2500 3000
0
500
1000
1500
2000
2500
3000
3500
4000
velocity
depth
VSP multi-layers velocity Model
Migration velocity analysis
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)
Tilted Ellipse RMOsVelocity ModelRMO After Migration
Vmig = Vtrue
Receiver DepthReceiver Depth, mVelocity, m/s
2600
2700
2800
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