Transcript Reciprocal offset-vector tiles

3DSymSam
Reciprocal offset-vector tiles in various geometries
by
Gijs J.O. Vermeer
3DSymSam – Geophysical Advice
From The Leading Edge, April 2007:
Wide-azimuth seismic acquisition
• “… by reciprocity, … a redundancy in the offset azimuth
distribution...” (Corcoran et al.)
• “… by using reciprocity, we can shoot off-end in the
crossline direction...” (Michell et al.)
• “… the coverage … falls in adjacent quadrants, not in
diagonal quadrants, which are redundant.” (Howard)
Question: Did we do things wrong all along in land data acquisition?
All conventional 3D geometries are sparse with corresponding
internal spatial discontinuities that can be mitigated by acquisition in
all four quadrants
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Outline Reciprocal offset-vector tiles (OVTs)
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Introduction
Orthogonal geometry
Areal geometry
Parallel geometry
– Narrow azimuth
– Wide azimuth
• Conclusions and final remarks
For each geometry:
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Basic subset of geometry with its edges
OVTs and OVT gathers
Reciprocal OVTs
Illumination by reciprocal OVT gathers
Reciprocal offset-vector tiles
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Outline Reciprocal offset-vector tiles
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•
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Introduction
Orthogonal geometry
Areal geometry
Parallel geometry
– Narrow azimuth
– Wide azimuth
• Conclusions and final remarks
• For each geometry:
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–
–
–
September 2007
Basic subset of geometry with its edges
OVTs and OVT gathers
Reciprocal OVTs
Illumination by reciprocal OVT gathers
Reciprocal offset-vector tiles
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Cross-spread in 8 x 8-fold orthogonal geometry
• 64 unit-cell sized areas in
each cross-spread
• 64 cross-spreads contribute
one tile each to each unit cell in
full-fold area
Unit cell
Vertical lines: source lines
Horizontal lines: receiver lines
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OVT gathers of 64-fold geometry
tiles along diagonal in first quadrant
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Short offsets
Medium short
offsets
Medium long
offsets
Long offsets
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Offset-vector tiles in 8 x 8-fold orthogonal geometry
OVT has small range of
offsets and azimuths
Reciprocal OVT has the
same average offset and
reciprocal azimuth
These reciprocal OVTs
share the same midpoints
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Reciprocal OVTs in orthogonal geometry
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Illumination
using single OVT gather
Illumination
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Illumination
Reciprocal offset-vector tiles
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Imaging
using single OVT gather
Horizon slice
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Horizon slice
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Illumination and imaging
using reciprocal OVT gathers
Illumination
Horizon slice
Reciprocal OVTs provide complementary illumination
(especially important for cross-spread edges)
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Outline Reciprocal offset-vector tiles
•
•
•
•
Introduction
Orthogonal geometry
Areal geometry
Parallel geometry
– Narrow azimuth
– Wide azimuth
• Conclusions and final remarks
• For each geometry:
–
–
–
–
September 2007
Basic subset of geometry with its edges
OVTs and OVT gathers
Reciprocal OVTs
Illumination by reciprocal OVT gathers
Reciprocal offset-vector tiles
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3D receiver in 8 x 8-fold areal geometry
OVT has small range of
offsets and azimuths
Reciprocal OVT has the
same average offset and
reciprocal azimuth
These reciprocal OVTs
share the same midpoints
Unit cell
Area of shots firing into
receiver in center
Midpoint area for receiver
in the center
Receiver unit (node)
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3D receiver in 8 x 8-fold areal geometry
These reciprocal OVTs
share the same midpoints
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Illumination
using single OVT gather
Shooting updip
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Shooting downdip
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Illumination
using reciprocal OVT gathers
Reciprocal OVTs provide complementary illumination
(especially important for 3D receiver edges)
September 2007
Reciprocal offset-vector tiles
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Outline Reciprocal offset-vector tiles
•
•
•
•
Introduction
Orthogonal geometry
Areal geometry
Parallel geometry
– Narrow azimuth
– Wide azimuth
• Conclusions and final remarks
• For each geometry:
–
–
–
–
September 2007
Basic subset of geometry with its edges
OVTs and OVT gathers
Reciprocal OVTs
Illumination by reciprocal OVT gathers
Reciprocal offset-vector tiles
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Dual source / 10 streamer parallel geometry
• Basic subset: dual-source
gather
• Crossline fold = 1
• Streamer length = 6000 m
• Source interval = 37.5 m
 Inline fold = 80
 80 OVTs in dual-source
gather
Midpoint area of dualsource gather
source lines
receiver lines
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OVTs in 80-fold narrow parallel geometry
3000 m
500 m
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OVTs in narrow parallel geometry
Parallel boat passes
Antiparallel boat passes
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OVTs in narrow parallel geometry
Antiparallel boat passes
In antiparallel acquisition reciprocal OVTs are put next to each other
This would reduce spatial discontinuities in crossline direction
Fully overlapping boat passes
In full overlap acquisition reciprocal OVTs are put on top of each other
This would reduce illumination irregularities in crossline direction
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Reciprocal OVTs in narrow parallel geometry
Fully overlapping boat passes
illumination with up-dip shooting
illumination with down-dip shooting
Reciprocal OVTs provide complementary illumination
(especially important for edges of dual-source gathers)
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Outline Reciprocal offset-vector tiles
•
•
•
•
Introduction
Orthogonal geometry
Areal geometry
Parallel geometry
– Narrow azimuth
– Wide azimuth
• Conclusions and final remarks
• For each geometry:
–
–
–
–
September 2007
Basic subset of geometry with its edges
OVTs and OVT gathers
Reciprocal OVTs
Illumination by reciprocal OVT gathers
Reciprocal offset-vector tiles
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BP WATS configuration
8 streamers @ 125 m; 2 x 2 sources
8100 m
inline source interval 150 m
inline fold = 8100 / 2 / 150 = 27
1000 m
Next: repeat everything after lateral shift of 250 m (crossline roll) 
crossline fold = 4000 / 2 / 250 = 8
(Threadgold et al, SEG 2006)
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Shell WATS configuration
8 streamers @ 150 m; 2 x 2 sources
9000 m
inline source interval 150 m
inline fold = 9000 / 2 / 150 = 30
1200 m
Next: repeat everything after lateral shift of 450 m (crossline roll) 
crossline fold = 7200 / 2 / 450 = 8
(Moldoveanu and Egan, FB 2006)
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Quad-source midpoint areas in WATS geometries
4050 m
BP:
Size OVT:
150 × 250 m
2000 m
No reciprocal OVTs
Crossline roll determines height of each horizontal strip of OVTs
4500 m
1800 m
Size OVT:
150 × 450 m
Shell:
Reciprocal OVTs
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Conclusions and final remarks
• Diagonal quadrants in sparse geometries provide
complementary illumination
• Reciprocal offset-vector tiles mitigate illumination
irregularities of sparse geometries
• This also applies to NATS and WATS: Wide is only wide if
all four quadrants are acquired
• Current WATS geometries are characterized by shortcuts
and other problems
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Crossline binsize
Crossline roll
Maximum crossline offset
No reciprocal OVTs
Lack of short offsets
• Feathering effects require extra streamers for regularization
• Areal geometry acquired with nodes does not suffer from
these geophysical shortcomings
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