Transcript No Slide Title

Kirchhoff vs Crosscorrelation
Migration
Kirchhoff Mig.
0.5 km
2.5 km
0.5 km
Crosscorr. Mig.
0.5 km
2.5 km
2.5 km
0.5 km
2.5 km
Kirchhoff vs Crosscorrelation
Migration
Kirchhoff Mig.
0.5 km
2.5 km
0.5 km
Crosscorr. Mig.
0.5 km
2.5 km
2.5 km
0.5 km
2.5 km
VSP Images with
Static Errors
Kirchhoff Mig.
0.5 km
2.5 km
0.5 km
Crosscorr. Mig.
0.5 km
2.5 km
2.5 km
0.5 km
2.5 km
VSP Images with
Static Errors
Kirchhoff Mig.
0.5 km
2.5 km
0.5 km
Crosscorr. Mig.
0.5 km
2.5 km
2.5 km
0.5 km
2.5 km
Field RVSP Images with
Static Errors
Kirchhoff Mig.
Crosscorr. Mig.
0.0 km
.9 km
0.0 km
.12 km
0.0 km
.12 km
Enhancing Illumination Coverage of
VSP by Crosscorrelation
Interferometric Migration
Imaging
Jianhua Yu
Gerard T. Schuster
University of Utah
Outline
Motivation
Crosscorrelation Migration
SEG/EAGE Model
2-D RVSP Field Data
Conclusions
Outline
Motivation
Crosscorrelation Migration
SEG/EAGE Model
2-D RVSP Field Data
Conclusions
Problems with VSP Imaging
Quality?
Limited recording aperture
Narrow illumination coverage
Static errors at VSP well
caused by location errors
Solution: Xcorr Migration of Ghost Reflections
Widens illumination coverage VSP
CDP
Solution: Xcorr Migration of Ghost Reflections
Widens illumination coverage VSP
CDP
Eliminates Rec. Statics: No Need to Know Rec. Location
Eliminates ~ ½ of the Raypath
Outline
Motivation
Crosscorrelation Migration
SEG/EAGE Model
2-D RVSP Field Data
Conclusions
Crosscorrelation Migration
Kirchhoff Migration of Crosscorelograms
m(x) =
(g, s, t + t )
s
s
g
g
gx
sx
s
g
How do you remove kinematic effects of propagating
through unintersting parts of medium?
Uninteresting Part of Medium
Pick Direct Arrival Time TM and shift all
Traces by TM
TM
{
M
Uninteresting Part of Medium
Pick Direct Arrival Time TM and shift all
Traces by TM
M
Uninteresting Part of Medium
Shifting Traces Removes Kinematic Effects
Of Propagating through Uninteresting Parts of Medium
M
Uninteresting Part of Medium
Shifting Traces Removes Kinematic Effects
Of Propagating through Uninteresting Parts of Medium
M
Uninteresting Part of Medium
Shifting Traces Removes Kinematic Effects
Of Propagating through Uninteresting Parts of Medium.
. to Surface
Source Moved
g
M
Kirchhoff Migrate psuedo-shot gathers
m(x) =
(g, t + t
M g
M
gx
Mx
)
Can replace time-shifted traces by crosscorrelograms
Interferometric Summary

Wider, taller coverage. Eliminates
well statics and uninteresting parts of
the medium.
VSP
Above Source
Imaging
{
?
Wider Coverage
Interferometric Summary

Wider, taller coverage. Eliminates
well statics and uninteresting parts of
the medium.
VSP
Above Source
Imaging
{
Wider Coverage
Kirchhoff Migrate psuedo-shot gathers
m(x) =
(g, t + t
M g
M
gx
Mx
)
Outline
Motivation
Crosscorrelation Migration
SEG/EAGE Model
2-D RVSP Field Data
Conclusions
Well
256 Sources
0
Depth (km)
V = 1.5 - 3.0 km/s
SEG/EAGE Model
2
0
X (km)
3
Acquisition Parameters:
Well
0
Well location: (1.5 km, 0 km)
1 km
Source interval: 10 m
Depth (km)
Source number: 256
Receiver interval: 10 m
Receiver depth range: 0.1 -1 km
Receiver number: 91
Sample interval: 1 ms
2
0
X (km)
3
Recording length: 3 s
0.2
Time (s)
0
3
Depth (km)
0.9
CSG 160
0.2
Time (s)
0
3
Depth (km)
0.9
Ghosts (CSG 160)
0
X (km)
2.4
1.4
X (km)
Time (s)
0
3
CRG 60
Xcross 60
2.4
Kirchh Mig (45)
Xcorr Mig (45)
Xcorr. Mig(15’)
Depth (km)
0.5
2.0
0.5
2.5
0.5
X (km)
2.5 0.5
2.5
0
Well Depth (m)
900
Static errors (ms)
50
Raw Data
-50
Static Errors at Well
Kirchhoff Migration
Static Error: 0
Static Error: 25 ms
Static Error: 50ms
Depth (km)
0.5
2.0
0.5
2.5
0.5
X (km)
2.5 0.5
2.5
Crosscorrelation Migration
Static Error: 0
Static Error: 25ms
Static Error: 50 ms
Depth (km)
0.5
2.0
0.5
2.5
0.5
X (km)
2.5 0.5
2.5
Velocity Model
Primary vs Multiple Image
0
Depth (km)
11
0
X (km)
16 0
X (km)
16
Contents
Motivation
Crosscorrelation Imaging Condition
SEG/EAGE Model
2-D RVSP Field Data
Conclusions
30
Time (s)
0
0.3
Depth (ft)
900
Raw Data(CRG15)
30
Time (s)
0
0.3
Depth (ft)
900
Ghosts
Field Data (CSG 25)
5
Raw data (muted)
24
5
0.2
Trace No.
1.4
1.2
Master trace
24
xcorr data (muted)
Time (s)
Time (s)
0.5
Trace No.
Master trace
Depth (ft)
200
1300
0
X (ft)
400
Standard mig
0
X (ft)
400
Xcorr. mig
Exxon Data
Standard
Depth (ft)
0
1100
Well data
Xcorr.
Outline
Motivation
Crosscorrelation Migration
SEG/EAGE Model
2-D RVSP Field Data
Conclusions
Crosscorrelogram Migration Conclusions
Increased illumination coverage in
the VSP image. VSP ->CDP
Eliminate the static errors in the
well
No need to know source (RVSP) or
receiver location (VSP)
Half sensitivity to velocity migration
errors than mult. migration by “mirrors”.
Conclusions
Loss of some lateral resolution?
Xcorr
Kirchhoff
vs
Narrow Angle
Wide Angle
Be careful about virtual multiple
Ghost is weaker than primary
Extra summation compared to KM
Acknowledgments
UTAM sponsors
Exxon for 2-D field data
J. Claerbout + J. Rickett
II evolved from daylight
imaging
Depth (ft)
200
1300
0
X (ft)
400
Standard mig
0
X (ft)
400
Xcorr. mig
Geological Model
X(km)
Depth(km)
0
0
3
(2001)
4
Migration Result Using Crosscorrelation Imaging
1.6
X (km)
2.1
0
Time (s)
Too simple?
2.2
Widen illumination?
If there are static errors in well?
Why Use Crosscorrelation
Migration?
Widen the illumination coverage
in the VSP image
VSP geometry
Xcorr
Equivalent
surface geometry
Seismic Ghost Reflection
Ghost
Direct
Find R(x,z) but not know source location
?
Seismic Seismic
Interferogram:
Correlate Traces
Ghost Reflection
Master
Ghost x Direct has kinematics ofGhost
primary
reflection
x Direct
Direct x Direct
1
}2
t
M
Kirchhoff Migrate psuedo-shot gathers
m(x) =
M
g
(g, tgx + tMx )
M
Well
Receiver
Ghost
Direct
Wave
Primary
Source
RVSP
Ghost Reflection Imaging Condition:
 sg '  g 'x  xg
g'
 sg '
s
 sg
 sg '
g
 xg
 g' x
x
 sg
After Crosscorrelation of Two Traces at
Locations g & g’
 sg '  g 'x  xg sg '
 sg  sg '
g'
 sg '
s
g
 xg
 g'x
x
 sg
After Crosscorrelation of Two Traces at
Locations g & g’
 g' x  xg
 sg  sg '
g'
g
s
 xg
 g'x
x
After Crosscorrelation of Two Traces at
Locations g & g’
 g' x  xg
 sg  sg '
g'
g
s
 xg
 g'x
x
Recall Green’s Theorem
Every Surface Point = Source Point
Why is there insensitivity to static
errors in the well?
g’
g
g
 '   'sg '  g ' x  xg
 'sg '  sg '   s
s
Static errors
x
 '   'sg '  g ' x  xg  'sg '
g
'
g
xcorr   g ' x  xg
Crosscorrelogram Migration

m(x)   Corr( D) g ' g (  g ' x  xg )dgdg '
Migrated Image
Crosscorrelation
Imaging Condition
Crosscorrelograms
Field Data
Well data
Depth (ft)
0
1100
Xcorr. Migration
Exxon Data
Well data
Depth (ft)
0
1100
Standard Migration