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3-D VS 2-D SEISMIC
- THE END RESULT IS A DATA VOLUME
VS A DATA SLICE.
- MIGRATION OF 3-D SEISMIC DATA GIVES
A MORE ACCURATE SUBSURFACE IMAGE.
- 3-D SEISMIC DATA COSTS MUCH MORE.
3D 1
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2D VS 3D COVERAGE
3D 2
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3D 3
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LINE B 2-D MIGRATED
2
3
2
3
Tensor Geophysical Service Corporation
3D 63D 4
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RAW DATA
3D MIGRATION
2D MIGRATION
3D 53D 5
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3D COLOR DISPLAY OF CHANNEL
3D 43D 6
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LINE B 3-D MIGRATED
2
3
2
3
Tensor Geophysical Service Corporation
3D 7
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Important parameters in a 3-D CMP gather
1. fold
2. shot-receiver offset distributions
3. shot-receiver azimuth distributions
3D 8
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x
z
y
R
R
R
R
s
s
s
s
x
z
Rss ss RR R
Narrow-azimuth survey Wide-azimuth survey
Two general classes of seismic surveys
3D 9
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Common Midpoint (CMP) coverage
CMP bin size is 10m x 10m
8
7
6
5
4
3
2
1
9
10
Fold
3D 10
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a shot into a patch of receivers
receiver
shot
20 m
20 m
3D 11
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CMP fold for two shots
10
9
8
7
Fold
6
5
4
3
2
1
Y
C
O
O
R
D
3D 12
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Two patches shot
shot 2
shot 1
patch 1 patch 2
3D 13
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Example shot - receiver pairs into CMP bins
8
7
6
5
4
3
2
1
9
10
Fold
Y
C
O
O
R
D
3D 14
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" IN - LINE "
" CROSS - LINE "
TOTAL CMP FOLD =
IN-LINE FOLD X CROSS-LINE FOLD
3D 15
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Example Shot - Receiver pairs that contribute fold to a bin
8
7
6
5
4
3
2
1
9
10
Fold
Y
C
O
O
R
D
3D 16
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CMP fold for three shots
8
7
6
5
4
3
2
1
9
10
Y
C
O
O
R
D
Fold
3D 17
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. . . . ..
. . . . .
.. . . . .
.
. . . . .
.
. . . . ..
. . . . ..
. . . . ..
. . . . ..
*
*
*
*
2370 m
group
1 2 42
43
44
45
46
47
87
88
30 m
in-line direction
Patch roll
- in-line roll is 120 m (fourstations)
- cross-line roll is 120 m (4 lines)
Which yields
- in-line CMP fold = 11
- cross-line CMP fold = 4
- total CMP fold = 44
- 15m X 15m CMP bin size
15m
4 shots associatedwith each patch
30 m
Balam SE Geometry
3D 18
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3D 19
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SUBSURFACE SPACING
D. sin max
V
4 . F=
1
. DIPstk2 . F
Where :
V = Vrms (or stacking velocity to target event)
Fmax = highest useable frequency at target event
= steepest dip of interest
DIPstk =
3D 21
X
max max
= max dip of an event on the stacked section
max
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SUBSURFACE SPACING
D
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Example azimuth distributions for CMP gathers from a multi-azimuth survey
3D 22
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Example azimuth distributions for a narrow-azimuth survey
3D 23
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FAR OFFSET DEPTH OF DEEPEST TARGET
NOTE : IF WE KNOW THERE IS A MULTIPLE-PROBLEM, WE CAN
INCREASE THIS SOME, OR IF WE ARE MORE
INTERESTED IN THE SHALLOWER ZONES, WE CAN
DECREASE THIS SOME.
3D 24
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Example offset distributions from a narrow azimuth survey
3D 25
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EFFECT OF INCREASING SPATIAL SAMPLE INTERVAL
STACKED SECTION WITH TRACE SPACING = 106.4 M
3D 26
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EFFECT OF INCREASING SPATIAL SAMPLE INTERVAL
MIGRATED SECTION WITH TRACE SPACING = 106.4 M
3D 27
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EFFECT OF INCREASING SPATIAL SAMPLE INTERVAL
STACKED SECTION WITH TRACE SPACING = 53.2 M
3D 28
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EFFECT OF INCREASING SPATIAL SAMPLE INTERVAL
MIGRATED SECTION WITH TRACE SPACING = 53.2 M
3D 29
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EFFECT OF INCREASING SPATIAL SAMPLE INTERVAL
STACKED SECTION WITH TRACE SPACING = 26.6 M
3D 30
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EFFECT OF INCREASING SPATIAL SAMPLE INTERVAL
MIGRATED SECTION WITH TRACE SPACING = 26.6 M
3D 31
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MIGRATION APERTURE
Xmig
ZXmig= Z tan
If is themeasured (e.g. from dipmeter log) or calculated(e.g. from previous seismic) dip angle, and Z is the depth of
the dipping bed, then Xmigwill be an overestimate.
Xmig= (T V2 DIPmig)/4
An alternate, more accurate formula is:
Where:
DIPmig= x, the ratio of measured time over unit distance of the dipping event on a migrated section,
T = 2-way time to the deepest part of the dipping event.
V= Vrms (or migration velocity) to the dipping event.
3D 32
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MIGRATION APERTURE
3D 33
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MIGRATION APERTUREX mig
ZX mig = Z tan
An alternate, more accurate formula is:
T = 2 way time to the deepest part of the dipping event
3D 32
If is the measured (e.g. from dipmeter log) or calculated(e.g. from previous seismic) dip angle, and Z is the depth of
the dipping bed, then X mig will be an overestimate
X mig2
(TV DIP= mig ) /4
Where:
mig =DIP X , the ratio of measured time over unit distance
V = V rms (or migration velocity) to the dipping event
of the dipping event on an amigr atedsection
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Area to be imaged
Migration aperture
Fold taper zone
Full-foldboundary
SURFACE COVERAGE PROFILE