Salt Flank Imaging by PS Interferometry

Salt Flank Imaging by PS Interferometry

Xiang Xiao

Univ. of Utah

Feb. 3

Outline

I. Motivation

II. Theory

III. Numerical Tests

IV. Field Data Examples

V. Conclusion

I. Motivation

• Goal:– Salt Flank Imaging with Migration of PS Transmission Waves;

• Method:

– Standard Migration (KM);

– Reduced-time Migration (RM), Sheley and Schuster, 2003;

– Interferometric Migration (IM), and Interferometric Redatuming (IR), Schuster, 2004;

Outline

I. Motivation

II. Theory



V. Conclusion

Uninteresting PartUninteresting Part of Mediumof Medium

Tim

eT

ime

Goal: Image Interface by PS Transmitted WavesGoal: Image Interface by PS Transmitted Waves

MM gg

ss

PP

d(M|d(M|ss)) d(g|s)d(g|s)

PPPPPPSS

d(M|d(M|ss)) d(g|s)*d(g|s)*((gg,,MM) =) =

m(m(xx)=)=

== e e eei wi w t + t + i wi w tt -i w-i w t - t - i wi w tt

PPSS PPPP

== e ei wi w ((t t –– tt))


Tim

eT

ime


MM gg

ss

PP


PPPPPPSS

ss

d(M|d(M|ss)) d(g|s)*d(g|s)*((gg,,MM) = ) =

m(m(xx)=)=


Tim

eT

ime


MM gg

ss

PP


PPPPPPSS

ss

d(M|d(M|ss)) d(g|s)*d(g|s)*((gg,,MM) = ) =

m(m(xx)=)=

Unique Specular Point Snell’s Law OKUnique Specular Point Snell’s Law OK

g,g,MM

((gg,,MM) ) m(x) =m(x) = eei wi w ((t t –– tt))––

xx xx

xxDatuming

Migration

Interferometric Interferometric PSPS Datuming Datuming

g,g,MM


xx xx

Eliminates src/rec statics and Eliminates src/rec statics and uninteresting parts of the medium.uninteresting parts of the medium.

Raise buried src to Raise buried src to interestinginteresting inter. inter.

Outline

I. Motivation

II. Theory



V. Conclusion

Salt Velocity ModelSalt S-wave Velocity ModelSalt P-wave Velocity Model

Dep

th

(m)

X (m)X (m) m/s m/s

III. Numerical test

P-to-S ratios = 30.5

0

12000 1200

4400

20000 1200

2540

1170

VSP Gathers

Time (s)

PS Waves Shot @ (0,0)

Time (s)

P Wave Shot @ (0,0)

Dep

th

(m)

III. Numerical test

Interferometric Interferometric PSPS Datuming Datuming

g,g,MM


xx xx

Eliminates src/rec statics and Eliminates src/rec statics and uninteresting parts of the medium.uninteresting parts of the medium.

Raise buried src to Raise buried src to interestinginteresting inter. inter.

Synthetic vs. Redatuming Data

Time (s)

Virtual after IR

Time (s)

Synthetic PS VSP

Dep

th

(m)

III. Numerical test

KM vs. IM with Correct Velocity Model

IMKM

Dep

th

(m)

X (m)X (m)

III. Numerical test

0

12000 1200

963

13130 1200

7E4

-8E4

KM, RM vs. IM

Constant Static Shift in Data

Each Trace Advances 60 ms

III. Numerical test

KMD

epth

(m

)

X (m)

0

1200

0 1200

400

-700

Haven’t been imagedBoundary is shifted

III. Numerical test

RMD

epth

(m

)

X (m)

0

1200

0 1200

850

-950

Correctly imaged

Poor focused

III. Numerical test

IMD

epth

(m

)

X (m)

0

1200

0 1200

7E4

-8E4

Correctly imaged

Strong focused!Small cover of PS ray

Additionally imaged

III. Numerical test

ComparisonD

epth

(m

)

X (m)

0

1200

0 1200

KMRM

IM

III. Numerical test

Incorrect Migration Model

KM, RM vs. IM

90% Velocity Above Salt

III. Numerical test

KMD

epth

(m

)

X (m)

0

1200

0 1200

850

-1000

Correct place

Incorrectly imaged

III. Numerical test

RMD

epth

(m

)

X (m)

0

1200

0 1200

850

-1000

Incorrectly imaged,Should image as black

boundary

Correctly imaged

III. Numerical test

Elliptical artifacts

IMD

epth

(m

)

X (m)

0

1200

0 1200

4E4

-6E4

Correctly imaged

Correctly imaged!

III. Numerical test

Elliptical artifacts are removed

Comparison

KMRM

IM

Dep

th

(m)

X (m)

0

1200

0 1200

III. Numerical test

Outline

I. Motivation

II. Theory



V. Conclusion

IV. Field Data

D

epth

(m

)

Offset (m)4878

0 1829

0

Well and Source Location

Source @150 m offset

P-to-S ratios = 2.7

Velocity ProfileS WaveP Wave

Dep

th

(m)

Velocity (m/s)

0

45000 5000 0 3000

2800 m

3200 m

Salt

IV. Field Data

Incorrect velocity model

P-to-S ratios = 1.6

150 X ComponentD

epth

(m

)

Traveltime (s)

2652

3887

1.2 3.0

Salt

Direct P

Reflect P

Alias (Reverberation)

IV. Field Data

Z ComponentD

epth

(m

)

Traveltime (s)

2652

3887

1.2 3.0

Salt

Direct P

Reflect P

Alias (Reverberation) Direct S

IV. Field Data

Processing Flow ChartOriginal Data

Reoriented

Pick desired events

Flatten, median filter, unflatten

Migration (KM, RM, IM)

Dep

th

(m)

Traveltime (s)

2652

3887

1.2 3.0

IV. Field Data

150 X Before Rotation

Dep

th

(m)

Traveltime (s)

2652

3887

1.2 3.0

IV. Field Data

150 X After RotationP wave energy was maximized

Dep

th

(m)

Traveltime (s)

2652

3887

1.2 3.0

III. Field Data

150 X PSS EventsTransmitted at upper boundary

150 X PPS EventsD

epth

(m

)

Traveltime (s)

2652

3887

1.2 3.0

III. Field Data

Transmitted at lower boundary

Migration of PSS

IV. Field Data

Ray Path Coverage

2000

4200

0 200

Dep

th

(m) SAL

T

Offset (m)

Migration of PSS

IV. Field Data

SALT

150 offset RM 150 offset IM

0 200 0 200Offset (m)

150 offset KM

2000

4200

0 200

Dep

th

(m)

Migration of PSS

IV. Field Data

SALT

Ray Path Coverage

2000

4200

0 200

Dep

th

(m)

Migration of PSS

IV. Field Data

SALT

Offset (m)

IV. Field Data

Migration of PPS

SALT

150 offset RM 150 offset IM

0 200 0 200

150 offset KM

2000

4200

0 200

Dep

th

(m)

Offset (m)

Migration of PPS

SALT

IV. Field Data

Outline

I. Motivation

II. Theory



V. Conclusion

IV. Conclusion

• Benefits of IM:– Remove influence of static shifts and migration velocity

errors;

– Eliminated source statics by correlation;

– Remove elliptical artifacts, boost migration image contrast;

• Drawbacks of IM:– Migration artifacts from stationary phase approximation;

– Extra summations and computation time;

– Small range of incidence angle than true SWI data;

– Worse vertical resolution than KM;

Thank you!

• Thank the sponsor of the 2004 UTAM consortium for their support.

Salt Flank Imaging by PS Interferometry

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