Transcript apa_blue

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Prestack Waveform Inversion: an Onshore
Application in the US Gulf Coast
August Lau, Chuan Yin, Mike Greenspoon,
Apache Corp; Anthony Vassiliou, GeoEnergy
September 2007
The following discussions contain certain “forward-looking statements” as defined by the Private Securities Litigation Reform Act of 1995 including, without limitation, estimates,
expectations, plans and goals regarding Apache’s production, reserves, financings, acquisitions, exploration and exploitation prospects, energy prices, operating costs, and results of
operations. Such forward-looking statements involve estimates, assumptions and uncertainties. No assurance can be given that Apache’s expectations or goals will be realized, and actual
results may differ materially from those expressed in the forward-looking statements. For reconciliations of non-GAAP financial measures, see our web site www.apachecorp.com.
Well to Seismic Tie
Well-to-seismic tie: zero-offset synthetic and PSTM final stack.
Displayed panels are (L to R): gamma-ray log, resistivity log, sonic
log, bulk density log, full-stack overlaid with zero-offset synthetic,
cross-correlation of the synthetic to surface seismic.
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Post-stack Rock Properties
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Pre-Stack Rock Properties
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Sand with Pay has Lower Vp / Vs Ratio and Lower P-impedance
Pay sand has lower
Vp / Vs and P- imp
Workflow
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Input PSTM Gather (Left) and Modeled Gather
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Starting and Final Models
Vp
Initial
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Vs
Final
Initial
Density
Final
Initial
Final
Applications of Pre-Stack Inversion
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 Estimation of Vp, Vs, density, Zp, Zs and their uncertainties for fluid
and lithology discrimination
 Through calibration and interpretation, thickness estimation, net to
gross estimation, porosity estimation
 Interpretation of small-scale or localized features, such as narrow
channels, slump faults, etc.
Full Stack Amplitude Extraction
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Well F
Well 3
Well A
2000’
Well B
Well D
Well C
Well E
Full Stack
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Cross Section
Main Producing Field
WELL F
WELL A
WELL E
Horizon A
Horizon B
WELL C
WELL B
5-20 Angle Stack
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Cross Section
Main Producing Field
WELL F
WELL A
WELL E
Horizon A
Horizon B
WELL C
WELL B
Arbitrary Line-Interpreted Lithology Cube
Main Producing Field
Cross Section
WELL F
WELL A
WELL E
Horizon A
Horizon B
WELL C
WELL B
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Vp/Vs Volume
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Well F
Well 3
Well A
2000’
Well B
Well D
Well C
Well E
DZP
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Well F
Well 3
Well A
2000’
Well B
Well D
Well C
Well E
DZS
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Well F
Well 3
Well A
2000’
Well B
Well D
Well C
Well E
Inversion Technique Differences
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Major Differences between Pre-stack Waveform Inversion
applied to gathers and angle-stack inversions:
 Pre-stack waveform inversion is applied directly on gathers
with NMO removed, preserving all amplitude, phase, offset
information
 Pre-stack waveform inversion is seismic data driven. Angle
stack inversion commonly well log driven
 Assuming long enough acquisition cable, pre-stack waveform
inversion estimates directly Vp, Vs, density
Inversion Technique Differences con’t.
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 Pre-stack waveform inversion can work with either only
primary reflections or with both primary and multiple
reflections
 Pre-stack waveform inversion applied directly on gathers
does not have to deal with the NMO stretch effect for long
cables
 Pre-stack waveform inversion makes use of interval
velocities.
 Pre-stack waveform inversion applied on gathers is not
sensitive to starting low frequency Vp / Vs / density model
Conclusions
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 Pre Stack Inversion is a faster, cheaper, and more accurate
method than traditional well-based inversion techniques
 Various output volumes can be calibrated with well control
for net pay estimations
 Prospects can be qualified with multi-cube interpretation
 A detailed geologic input model is not necessary to
produce results
Acknowledgements
 Seismic Data Courtesy of Seitel
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