Adaptive Ground Roll Attenuation - CGG

PROCESSING & IMAGING
AGORA
Adaptive Ground Roll Attenuation
Where ground roll characteristics vary across a survey the standard methods, such as FK
and radon techniques which use fixed parameterization and regular grids, become ineffective.
AGORA Adaptive Ground Roll Attenuation provides accurate attenuation by adapting to the
ground roll characteristics in 2D and 3D domains. The ground roll is modeled and adapted to
the data in a least-squares sense before subtraction. This provides robust and effective ground
roll attenuation, even on external cables and in challenging conditions where noise is aliased or
dispersive, whilst ensuring excellent preservation of primaries. AGORA is also used to attenuate
guided waves allowing wider mutes, improved velocity picking, increased signal-noise ratio in the
stack and providing more far-offset data for full AVO studies.
AGORA removes the ground roll more effectively than FK methods and also gives better preservation of the amplitudes of the body waves in the near-offset cone.
FEATURES:
• Adaptive attenuation of spatially variant ground roll and guided
wave energy
• Fully data-driven
• Flexible non-linear attenuation using an FX Modeling with a
Wavelet Transform scheme
• Does not require regular spatial sampling
• Effective against aliased and dispersive ground roll
Safer, Clearer, Better
Get to Know Our SeisAble Benefits
Raw shot FK filtering AGORA
BENEFITS:
• Preserves the amplitudes of both P and S body waves
• Preserves data bandwidth
• More accurate ground roll attenuation recovers better quality
near-offset data for improved stack response
• Guided wave attenuation recovers far-offset data allowing:
- wider mute, more accurate velocity picking
- more reliable AVO analysis
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PROCESSING & IMAGING
1 = 300m/s 2 = 500m/s 3 = 600m/s 4 = 700m/s
The spatial variations of the ground roll characteristics across a survey area.
DATA-DRIVEN GROUND ROLL ATTENUATION
Stack of the input data. Stack after AGORA adaptive filtering of the ground roll on shots.
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Ground roll is the result of interfering P and SV waves that travel
along or near the ground’s surface. They are characterized by their low
velocity, low frequency and high amplitude. Ground roll can be strongly
dispersive and aliased, and can also act as guided waves (sometimes
called higher modes) - this means that for each frequency there are
different phase velocities.
Local variation of these characteristics is common and is clearly visible
on these shot gathers from different locations of the same survey.
Frequency content, group and phase velocity, amplitude and degree of
aliasing vary spatially between these locations.
AGORA is a data-driven approach which includes:
• automatic extraction of the ground roll characteristics (Frequency-
Velocity panels)
• splitting data into frequency-wave number bands using a
high-resolution reversible wavelet transform
• modeling of the ground roll in the FX domain using a least-squares
iterative approach
AGORA provides accurate attenuation by adapting to the ground roll
characteristics in different 2D and 3D domains such as 2D shot or
receiver, cross-spread and 3D common receiver or common shot. This
flexible approach enables accurate modeling even on broadside cables in
3D data where the ground roll is hyperbolic.
Europe, Africa and Middle East
processing.eame@cggveritas.com
Americas
processing.nasa@cggveritas.com
Asia-Pacific
processing.apac@cggveritas.com
11F-PI-212-V1