Michelle Montano* Don Lawton Gary Margrave

Outline

Introduction Theory

— Spectral-ratio method — Dominant frequency matching

Study area Synthetic VSP data analysis Field VSP data analysis Conclusions Acknowledgements

1

Introduction

2

Down-going waves propagating to the borehole receivers. • The downgoing wavefield give us

access to the wavelet at different receiver depths.

• Oversaturation in the amplitudes in the shallow receivers results in an overestimation of Q.

• Shallow layers are expected to show low Q values because poorly consolidated rocks are usually present.

S

R

Introduction

3

Up-going waves propagating to the borehole receivers.

• Using the upgoing wavefield may help to estimate Q in the shallow layers.

• Reflectors can be used as secondary sources.

• In this case the source would be farther from the shallow receivers.

S

S*

R

Theory

4

Study Area

5

VSP Geometry

• Fourteen source points with dynamite and an EnviroVibe source.

• 222 receivers at 2m spacing (60-500m depth).

Taken from, Hall et al. (2012)

Well log data

6

Density and p-wave velocity logs, blocked into five horizontal layers.

Synthetic VSP data analysis

7

Forward Modelling using well log data from Well B.

30m

10m

Receiver Depth

Synthetic VSP data analysis

8

Forward Modelling using well log data from Well B.

50m

10m

Receiver Depth

Synthetic VSP data analysis

9

Forward Modelling using well log data from Well B.

80m

10m

Receiver Depth

10

𝑑=30𝑚 𝑑=50𝑚

𝑑=80𝑚

Down-going wavefield

Synthetic VSP data analysis

11

Forward Modelling based on Well B, showing up-going events. Flipped in depth

12

𝑑=30𝑚 𝑑=50𝑚

𝑑=80𝑚

Up-going wavefield

Field VSP Data Analysis Dynamite Source

13

Field VSP Data Analysis

14

100

200

300

400

500

Rec. Depth (m)

100

200

300

400

500

600

700

Tim

e (m

s)

Seismic gather: Shot point 1 using a dynamite source (Z component)

Amplitude Spectra – Downgoing wavefield

15

50

100

150

200

250

300

350

400

450

100

200

300

400

500

Rec. Depth (m)

Freq

. (Hz

)

-10dB

-20dB

-30dB

-40dB

0dB

-50dB

-60dB

Amp

Shot point 1 using a dynamite source (Z component)

16

50

100

150

200

250

Tim

e (m

s)

100

200

300

400

500

Rec. Depth (m) Freq (Hz)

100

200

300

400

500

0

Cum. Attenuation

0.00

4

0.00

8

0.01

2

0

200

300

400

500

100

Depth (m)

Spectral-ratio method from VISTA software Frequency band: 30-130 Hz

Field VSP Data Analysis

17

100

200

300

400

500

600

700

Tim

e (m

s)

100

200

300

400

500

Flipped Rec. Depth (m)

Seismic Gather: Shot point 1 using a dynamite source (Z component) - Flipped

Amplitude Spectra - Upgoing wavefield

18

100

200

300

400

500

Flipped Rec. Depth (m)

-10dB

-20dB

-30dB

-40dB

0dB

-50dB

-60dB

Amp

50

100

150

200

250

300

350

400

450

Freq

. (Hz

)

Shot point 1 using a dynamite source (Z component)

19

Freq (Hz)

100

200

300

400

500

0

Cum. Attenuation

0.01

0.02

0.03

0 0.04

100

200

300

400

500

Rec. Depth (m)

550

600

650

700

750

Tim

e (m

s)

Spectral-ratio method from VISTA software

Depth

Field VSP Data Analysis EnviroVibe Source

20

Field VSP Data Analysis

21

100

200

300

400

500

600

700

Tim

e (m

s)

100

200

300

400

500

Rec. Depth (m)

Seismic Gather: Shot point 1 using an EnviroVibe source (Z component)

Amplitude Spectra - Downgoing wavefield

22

100

200

300

400

500

Rec. Depth (m)

50

100

150

200

250

300

350

400

450

Freq

. (Hz

)

-10dB

-20dB

-30dB

-40dB

0dB

-50dB

-60dB

Amp

Shot point 1 using an EnviroVibe source (Z component)

23

50

100

150

200

Tim

e (m

s) 200

300

400

500

100

Depth (m)

100

200

300

400

500

Rec. Depth (m) Freq (Hz)

100

200

300

400

500

0

Cum. Attenuation

0.00

4

0.00

8

0.01

2

0

Spectral-ratio method from VISTA software. Frequency band: 30-250 Hz

24

50

100

150

200

Tim

e (m

s)

100

200

300

400

500

Rec. Depth (m) Freq (Hz)

100

200

300

400

500

0

Cum. Attenuation

0.00

4

0.00

8

0.01

2

0

200

300

400

500

100

Depth (m)

Spectral-ratio method from VISTA software. Frequency band: 30-130 Hz

EnviroVibe Source

25

Field VSP Data Analysis

26

100

200

300

400

500

Rec. Depth (m)

200

400

600

800

1000

Tim

e (m

s)

Seismic Gather: Shot point 1 using an EnviroVibe source (Hmax component)

Amplitude Spectra - Downgoing shear wave

27

100

200

300

400

500

Rec. Depth (m)

50

100

150

200

250

300

350

400

450

Freq

. (Hz

)

-10dB

-20dB

-30dB

-40dB

0dB

-50dB

-60dB

Amp

Shot point 1 using an EnviroVibe source (Hmax component)

28

100

200

300

Rec. Depth (m)

400

600

800

1000

Tim

e (m

s)

Freq (Hz)

20

40

60

0

Cum. Attenuation

0.04

0.08

0

200

300

400

500

100

Depth (m)

Spectral-ratio method from VISTA software. Frequency band: 10-40 Hz

Q estimation from down-going wavefield

29

Spectral-ratio method from VISTA software

A B

QP estimations using dominant frequency

30

CREWES Toolbox

Conclusions

31

Conclusions

32

Acknowledgements

Don Lawton Gary Margrave Unidentified company for access to the field VSP

data CREWES sponsors NSERC through grant CRDPJ 379744-08. GEDCO/Schlumberger for VISTA software CREWES students and staff

33

Thanks!

References

Aki K., and Richards, P. G., 2002, Quantitative Seismology 2nd Edition, University Science Book.

Cheng, P., Margrave, G. F., Comparison of Q-estimation methods: an update: CREWES Research Report, 25, 14.1-14.38.

Hinds, R. C., Anderson, N. L., and Kuzmiski, R. D., 1996, VSP Interpretive Processing: Theory and Practice, Soc. Expl. Geophys.

Kjartansson, E., 1979, Constant Q-Wave Propagation and Attenuation, Journal of Geophysical Research, 84, 4737-4748.

Margrave, G. F., 2013, Q tools: Summary of CREWES software for Q modelling and analysis: CREWES Research Report, 25, 56.1-56.22.

Margrave, G. F, 2013, Method of Seismic Data Processing. Course Lecture Notes, Univ. of Calgary.

Margrave, G. F., 2014, Synthetic seismograms with Q and stratigraphic filtering: CREWES News, 26, Issue 2, p. 6-7.

Quan, Y., and Harris, J. M., 1997, Seismic attenuation tomography using the frequency shift method: Geophysics, 62, 895-905.

Hall, K. W., Lawton, D. C., Holloway, D., and Gallant, E. V., 2012, Walkaway 3C-VSP: CREWES Research Report, 24, 9.1-9.26.

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 OutlineIntroductionIntroductionTheoryStudy AreaWell log dataSynthetic VSP data analysisSynthetic VSP data analysisSynthetic VSP data analysis Synthetic VSP data analysisSlide Number 13Field VSP Data AnalysisField VSP Data AnalysisAmplitude Spectra – Downgoing wavefield Field VSP Data AnalysisAmplitude Spectra - Upgoing wavefield Field VSP Data AnalysisField VSP Data AnalysisAmplitude Spectra - Downgoing wavefield   Field VSP Data AnalysisAmplitude Spectra - Downgoing shear wave Q estimation from down-going wavefieldQP estimations using dominant frequencyConclusionsConclusionsAcknowledgementsReferences