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

2. Downward continuation with joint NMO analysis

1

2

Reflector A

Reflector B

6

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

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