Estimating seismic attenuation (Q) Estimating seismic attenuation (Q) from VSP data at a heavy-oil field: from VSP data at a heavy-oil field:

Ross Lake, SaskatchewanRoss Lake, Saskatchewan

Arnim B. Haase and Robert R. StewartArnim B. Haase and Robert R. Stewart

CREWES Project, University of CalgaryCREWES Project, University of Calgary

OutlineOutline

IntroductionIntroduction Motivation, locationMotivation, location New Q-applicationsNew Q-applications Review of analytical signal method for Review of analytical signal method for

Q-estimation Q-estimation QQpp estimation from downgoing P-wave estimation from downgoing P-wave

isolated from offset VSPisolated from offset VSP QQss estimation from upgoing C-wave estimation from upgoing C-wave

isolated from offset VSPisolated from offset VSP ConclusionsConclusions

(Calderón-Macías et al., 2004)

Ross Lake Oilfield

Ross Lake, Saskatchewan – View of field and well 11-25

11-25 well site with VSP survey underway

Separated Downgoing P-Wave Field (54m offset source – vertical vibrator)

Separated Downgoing S-WaveField (54m offset src. – horizontal vibrator)

Previous Results

MethodSpectral

RatioDrift

CorrectionEmpirical Equation

Convolutional/WE Modeling

Average

QP 67 37 to 41 57 80/84 61

QS 23 37 11 24

Complex trace analysis (Engelhard et al., 1986; Tonn, 1991)

( ) ( ) cos ( )u t a t t

0

( ) ( ) ( ) 2 ( ) i tz t u t iv t U e d

2 2( ) ( ) ( )a t u t v t

Time derivative of complex trace (Engelhard et al., 1986)

0

'( ) 2 ( ) i tz t i U e d

Instantaneous frequency (Engelhard et al., 1986)

' '( )( )

2

d t z z zzt

dt izz

Log instantaneous amplitude ratio (Engelhard et al., 1986; Tonn, 1991)

( )2 2ln ln ( ) ( )1 2( ) 41 1

a t G tt t

a t G Q

Separated Downgoing P-Wave Field (400m offset source – vertical vibrator)

Instantaneous Amplitude of Separated Downgoing P-Wave Field

Log Spreading Ratio versus Q for Downgoing P-Wave Field at 303m Depth

Current estimate: Qp=44

Previous range: 37 to 84

Log Amplitude Ratio versus Δt for Downgoing P-Wave Field

Linear Fit of Log Amplitude Ratio versus Δt for Downgoing P-Wave Field

Linear Fit of Log Amplitude Ratio versus Δt for Downgoing P-Wave Field

Separated Upgoing C-Wave Field (400m offset source – vertical vibrator)

Instantaneous Amplitude of Separated Upgoing C-Wave Field

Log Spreading Ratio versus Q for Upgoing C-Wave Field at 933m Depth

Current estimate: Qs=28

Previous range: 11 to 37

Log Amplitude Ratio versus Δt for Upgoing C-Wave Field

Linear Fit of Log Amplitude Ratio versus Δt for Upgoing C-Wave Field

Linear Fit of Log Amplitude Ratio versus Δt for Upgoing C-Wave Field

Q versus Depth Station

(Calderón-Macías et al., 2004)

* *

···*···*

ConclusionsConclusions

New Q estimates within range of previous New Q estimates within range of previous resultsresults

Log amplitude ratio versus Log amplitude ratio versus ΔΔt curves are t curves are almost straight for P-wavesalmost straight for P-waves

Log amplitude ratio versus Log amplitude ratio versus ΔΔt curves nt curves not as ot as smooth for C-waves but still useful for Qsmooth for C-waves but still useful for Qss

Results need to be verified by synthetic Results need to be verified by synthetic examples examples

Transmission effects should be Transmission effects should be investigatedinvestigated

Acknowledgements

Thank you to Husky Energy Inc., in particular Mr. Larry Mewhort, for release of the VSP-data. Support by the CREWES team and its industrial sponsorship is gratefully acknowledged.