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Variable depth streamer technology for enhanced seismic interpretation
Gregor Duval*, Steven Bowman, Roger Taylor, Yves Lafet,
Adrian Smith and Henning Hoeber
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Content
Introduction: why does the seismic interpreter need
broadband data?
Benefits for interpretation of a wide range of geological
settings:
– Tertiary silici-clastic reservoirs
– Chalk section
– Deep sub-BCU targets
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Why does the seismic interpreter
need broadband data?
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Effects and benefits of increasing the bandwidth
Increasing high frequencies
10-20Hz 10-25Hz 10-30Hz 10-35Hz
2-20Hz 5-20Hz 10-20Hz
Large side-lobes and
broad central peak Sharper
central peak
Increase low frequencies
Reduced
side-lobes
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Effects and benefits of increasing the bandwidth
Conventional
BroadSeis
1000 m
20 m
BroadSeis Conventional
Courtesy of Total, Cobalt and the Republic of Gabon
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Effects and benefits of increasing the bandwidth
Courtesy of Total, Cobalt and the Republic of Gabon
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CPI log showing thin/complex formations
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Seismic synthetic model
Conventional seismic
synthetic
Conventional seismic data
at well location
Broadband seismic
synthetic Impedance
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Seismic synthetic model
Conventional seismic
synthetic
Conventional seismic data
at well location
Broadband seismic
synthetic Impedance
Prominent side-lobe interfering with interpretation of conventional seismic data
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Seismic synthetic model
Conventional seismic
synthetic
Conventional seismic data
at well location
Broadband seismic
synthetic Impedance
Peaks and troughs fit better with well marker
on broadband model
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Seismic synthetic model
Conventional seismic
synthetic
Conventional seismic data
at well location
Broadband seismic
synthetic Impedance
Obvious impedance gradient
Obvious impedance gradient
No impedance gradient
NB: The low frequency component of broadband data give a better feel of the actual impedance gradients, which should in turn provide better seismic inversion results
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Interpretation of Tertiary silici-clastic reservoirs
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Conventional – Interpretation of a gas reservoir
Side lobes
GR IP
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Broadband – Interpretation of a gas reservoir
GR IP
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Broadband – Interpretation of a gas reservoir
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Broadband – Interpretation of a gas reservoir
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Broadband – Interpretation of a gas reservoir
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Broadband – Interpretation of a gas reservoir
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Conventional – Ip from AVO inversion
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Broadband – Ip from AVO inversion
BroadSeis pre-stack inversion gives a more stable result: 1 – The GWC flat spot is better resolved 2 – Values of Ip within the gas column are more accurate and more homogeneous
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Conventional – Tay fan imaging (zoomed)
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Broadband – Tay fan imaging (zoomed)
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Broadband filtered – Tay fan imaging
Bandpass filter applied: 10-40Hz – 50-70Hz to approximately match spectrum of Conventional data
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Conventional – Tay fan imaging
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Conventional – Low frequency Tay fan imaging
Bandpass filter applied: 0-4Hz – 6-10Hz
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Broadband – Low frequency Tay fan imaging
Bandpass filter applied: 0-4Hz – 6-10Hz
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Conventional – Tertiary channel interpretation
Mey channel
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Broadband – Tertiary channel interpretation
Top Mey sandstone
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Broadband – Tertiary channel interpretation
Top Mey sandstone
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Conventional – Section through polygonal faults and contourites
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Broadband – Section through polygonal faults and contourites
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Conventional – Shallow section interpretation
Autopicking with waveform correlation tool on a wide window is noisy (spiky) on band limited data
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Broadband – Shallow section interpretation
Autopicking works a lot better on Broadband data, less spiky
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Interpretation of Chalk facies
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Conventional – Well tie and Chalk interpretation
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Broadband – Well tie and Chalk interpretation
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Broadband – Well tie and Chalk interpretation
This low impedance, marly interval correlates with the edge of a bright amplitude dissolution feature in the upper chalk section on the
seismic data.
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Conventional – Ekofisk/Maureen RMS amplitude map
Upper Chalk clay ponds and dissolution features
1km
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Broadband – Ekofisk/Maureen RMS amplitude map
1km
Upper Chalk clay ponds and dissolution features
The chalk dissolution features (clay pools) are much better defined on broadband data
The gray scale trends in the background highlight the regional facies variations: darker grays to the left are indicative of a marlier chalk
section whereas light grays correspond to hard, carbonate-rich chalk.
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A recent Chalk discovery: Orchid
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Orchid as interpreted on conventional data
41 Source: Trap Oil investor presentation
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W-E regional seismic line with interpretation
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Orchid
Salt-induced high
Zechstein
salt West Central shelf
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S-N regional seismic line with interpretation
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Orchid
Salt-induced high
Zechstein
salt
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W-E seismic line across Orchid
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Phase reversal due to ‘soft’ response
from the oil-filled chalk reservoir?
Flat-spot or porosity
effect (or both)?
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NE-SE arbitrary seismic line across Orchid
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Central Orchid is offset by a large fault initiated
due to uplift from the Zechstein salt below
Large salt diapir
towards the NW
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Orchid chalk reservoir as interpreted on broadband data
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TWT structure map Top Chalk amplitude map Minimum amplitude map directly below Top Chalk
Broadband data do not show amplitude dim in the
central part of the field
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Interpretation of deep sub-BCU targets
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Fault blocks interpretation using band-limited data
Cross fault correlation with multiple choices ?? Any reflector can be correlated through faults
?
?
?
?
?
BCU
Jurassic fault blocks
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Fault blocks interpretation using broadband data
Cross fault correlation better understood Uniqueness of the reflector correlation through faults
BCU
Jurassic fault blocks
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Conventional – Jurassic fault blocks interpretation
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Broadband – Jurassic fault blocks interpretation
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Broadband – Jurassic fault blocks interpretation
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Conventional – Jurassic fault blocks interpretation
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Conventional – Well synthetic, deep tie
NB: Well synthetic phase reversed for display purposes
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Broadband – Well synthetic, deep tie
NB: Well synthetic phase reversed for display purposes
Low frequency
package
This sub-BCU low frequency package is clearly visible on broadband seismic but not on conventional data, and it is replicated by a well
seismic synthetic. This means that this is the genuine formation signature and that the low frequencies below the BCU are not coming from
any kind of noise.
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Summary – Benefits for qualitative interpretation
BroadSeis data provide a broader frequency spectrum enabling the interpreter to:
Accurately interpret stratigraphy, thin beds and subtle structures – benefit
from the high frequencies
Produce a clearer interpretation of deep targets (sub-BCU, sub-chalk, sub-basalt…) and large-scale and subtle facies variations – benefit from the low frequencies
Extract the ‘true’ seismic signature of the geological formations by reducing the wavelet side-lobes and sharpening its central peak – benefit from the broad frequency range
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Broadband shallow imaging
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Acknowledgments
CGG multi-client division for permission to show these
data examples
Steven Bowman, James Rigg and Steve Thompson -
interpretation of seismic data and images contribution
Vincent Durussel, Steve Hollingworth and their team -
seismic processing
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THANK YOU!
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