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Estimating seismic attenuation (Q) from VSP data at a heavy-oil field: Ross Lake, Saskatchewan
Arnim B. Haase and Robert R. Stewart CREWES Project, University of Calgary
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Outline Introduction Motivation, location New Q-applications Review of analytical signal method for Q-estimation Qp estimation from downgoing P-wave isolated from offset VSP Qs estimation from upgoing C-wave isolated from offset VSP Conclusions
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(Calderón-Macías et al., 2004)
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Ross Lake Oilfield
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Ross Lake, Saskatchewan – View of field and well 11-25
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11-25 well site with VSP survey underway
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Separated Downgoing P-Wave Field (54m offset source – vertical vibrator)
Separated Downgoing S-WaveField (54m offset src. – horizontal vibrator)
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Convolutional/WE Modeling
Previous Results Method Spectral Ratio Drift Correction Empirical Equation Convolutional/WE Modeling Average QP 67 37 to 41 57 80/84 61 QS 23 37 11 24
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Complex trace analysis (Engelhard et al., 1986; Tonn, 1991)
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Time derivative of complex trace (Engelhard et al., 1986)
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Instantaneous frequency (Engelhard et al., 1986)
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Log instantaneous amplitude ratio (Engelhard et al., 1986; Tonn, 1991)
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Separated Downgoing P-Wave Field (400m offset source – vertical vibrator)
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Instantaneous Amplitude of Separated Downgoing P-Wave Field
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Log Spreading Ratio versus Q for Downgoing P-Wave Field at 303m Depth
Current estimate: Qp=44 Previous range: 37 to 84 Log Spreading Ratio versus Q for Downgoing P-Wave Field at 303m Depth
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Log Amplitude Ratio versus Δt for Downgoing P-Wave Field
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Linear Fit of Log Amplitude Ratio versus Δt for Downgoing P-Wave Field
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Linear Fit of Log Amplitude Ratio versus Δt for Downgoing P-Wave Field
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Separated Upgoing C-Wave Field (400m offset source – vertical vibrator)
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Instantaneous Amplitude of Separated Upgoing C-Wave Field
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Log Spreading Ratio versus Q for Upgoing C-Wave Field at 933m Depth
Current estimate: Qs=28 Previous range: 11 to 37 Log Spreading Ratio versus Q for Upgoing C-Wave Field at 933m Depth
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Log Amplitude Ratio versus Δt for Upgoing C-Wave Field
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Linear Fit of Log Amplitude Ratio versus Δt for Upgoing C-Wave Field
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Linear Fit of Log Amplitude Ratio versus Δt for Upgoing C-Wave Field
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Q versus Depth Station
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(Calderón-Macías et al., 2004)
* * ···* ···* (Calderón-Macías et al., 2004)
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Conclusions New Q estimates within range of previous results
Log amplitude ratio versus Δt curves are almost straight for P-waves Log amplitude ratio versus Δt curves not as smooth for C-waves but still useful for Qs Results need to be verified by synthetic examples Transmission effects should be investigated
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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.
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