Geol 755: Basin Analysis
Geophysics Week 4
Bright Spots As They Used To Be
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Used to be hard to preserve amplitude in processing
John N. Louie, Presenter
Reservoir Identification
Bright Spots As They Used To Be
The Character of a Modern Bright Spot
Bright Spots, Flat Spots, Dim Spots and Phase Changes
Phase Problems and Multiple Contacts
Use of Frequency, AVO and Shear Waves
Bright Spot & Flat Spot
terminate together
(Tegland,
Tegland, 1973)
Philosophy of Reflection Identification
Validating Hydrocarbon Indicators
Occurrence of Hydrocarbon Indicators
Taken From: Alistair R. Brown
Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Bright Spots As They Used To Be
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Classic flat spot (Backus & Chen, 1975), unconformable with adjacent reflections
Bright Spots As They Used To Be
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180° phase change, cap/brine sand to cap/gas sand
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
1
The Character of a Modern Bright Spot
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Various fluid interfaces and associated characteristics (European Polarity, 0°)
Add fluids to original impedances to get character
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
The Character of a Modern Bright Spot
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The Character of a Modern Bright Spot
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Gulf of Mexico gas reservoir, 0°-phase
The Character of a Modern Bright Spot
 Validity Checks for Flat Spots:
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Flat Spot
Flat Spot
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Flat
Bright
1 Symmetrical Trough (0°-phase)
At downdip limit of bright events
Unconformable with bright events
Flat Spot Flat Spot
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
2
The Character of a Modern Bright Spot
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Structure map of lower reflection- area of flat spot (purple)
Bright Spots, Flat Spots, Dim Spots and Phase Changes
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Gulf of Mexico Bright Spots & Flat Spots (0°-Phase, American Polarity)
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Flat Spots black
Reservoir tops red
Tertiary rocks
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Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Bright Spots, Flat Spots, Dim Spots and Phase Changes
Bright Spots, Flat Spots, Dim Spots and Phase Changes
Troll field, Norway: 7-km-long flat spot in Jurassic with 28% porosity
Not quite flat due to wave effects, but still unconformable
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Netherlands lower-Permian sandstone, 18% porosity
Anhydrite gives strongest reflections
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
3
Bright Spots, Flat Spots, Dim
Spots and Phase Changes
Bright Spots, Flat Spots, Dim
Spots and Phase Changes
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Proven reservoirs, North Sea
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North Sea reservoir
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Below, reservoir is full of
hydrocarbon to base at center of
anticline
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Above, reservoir-top horizon slice
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Below, fluid-contact reflection
horizon slice
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Amplitude rendered on slices
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Similar patterns show we are
looking at top and bottom of
same interval
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Bright Spots, Flat Spots, Dim Spots and Phase Changes
Bright Spots, Flat Spots, Dim Spots and Phase Changes
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Dim Spot Example
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Impedance contrast of
reservoir with
embedding medium is
small- reservoir is
cemented
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Australia NW Shelf:
Dim Spots.
Soft marine shale
capping reservoir
has slightly lower
impedance than gas
sands
Unconformity
reflection dims
where it truncates
reservoirs
Outside reservoir,
impedance contrast is
greater- so stronger
reflections
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
4
Bright Spots, Flat Spots, Dim Spots and Phase Changes
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180° phase change downdip of bright spot; various gains and colors
Bright Spots, Flat Spots, Dim Spots and Phase Changes
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Gulf of Mexico: 180° phase change- blue/red for gas is European polarity
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Bright Spots, Flat Spots, Dim Spots and Phase Changes
Bright Spots, Flat Spots, Dim Spots and Phase Changes
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Australia NW Shelf: 180° phase change- red/blue gas is American polarity
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Horizon slice we’
we’ve seen before
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Can
misinterpret
phase change
as fault
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Add structural
contours
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Bright part of channel
is higher than dim
part
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Validates gas content
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
5
Bright Spots, Flat Spots, Dim Spots and Phase Changes
Bright Spots, Flat Spots, Dim Spots and Phase Changes
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Horizon slice we’
we’ve seen before
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Thick gas sand
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3D view
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Flat Spot sags
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Bright part of
channel is higher
than dim part
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Validates gas
content
Gas sand has lower
impedance, lower
seismic velocity
Reflections coming
through gas sand
are delayed
Delay looks like a
sag in our time
sections
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False structure
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown,
Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Bright Spots, Flat Spots, Dim Spots and Phase Changes
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Thick gas sand
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Use a more
complex triplegradational color
bar to show faults in
weak reflections
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Internal structure of
gas reservoir
illuminated in bright
spot
Bright Spots, Flat Spots, Dim
Spots and Phase Changes
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Horizon slice with high
amplitudes caused by gas
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Well 7X produces from this
interval; 10X does not.
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
6
Phase Problems and Multiple Contacts
Bright Spots, Flat Spots, Dim Spots and Phase Changes
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Horizon-slice amplitude anomaly produced by oil
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Offshore China flat spot and bright spot in 90° data
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Sharp water-level
termination
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Dimming toward
unconformity
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Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Phase Problems and Multiple Contacts
Use of Frequency, AVO and Shear Waves
Offshore Indonesia: Stacked flat spots are dual fluid interfaces?
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Interference of strong internal reflections breaks up flat spot
Impedance must keep increasing, so should have same sign
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Gas reservoir should cut high frequencies?
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Reservoirs should have low interval velocities
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AVO- Amplitude Variation with Offset
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Instantaneous frequency seismic attribute
Hard to get stable interval velocities, especially deep
Based on how reflection coefficients vary with angle of wave incidence
Reservoirs have fundamentally different AVO compared to most other
reflections- if reservoir Poisson’
Poisson’s ratio is distinctive
Requires looking at pre-stack data with more noise, 4+ dimensions
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
7
Use of Frequency, AVO and Shear Waves
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Louie 1990 paper looking at fluids in the deep crust
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Use of Frequency, AVO and Shear Waves
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AVO trends rendered as a seismic attribute into the 2D section
J. N. Louie, 1990, Physical properties of deep crustal reflectors in southern
California from multioffset amplitude analysis: Geophysics, 55,
55, 670-681.
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Use of Frequency, AVO and Shear Waves
Use of Frequency, AVO and Shear Waves

Gulf of Mexico horizon offset section with AVO increase
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
8
Use of Frequency, AVO and Shear Waves

Use of Frequency, AVO and Shear Waves
Poisson’
Poisson’s ratios more directly accessed by S-wave reflections
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Use of Frequency, AVO and Shear Waves
Use of
Frequency,
AVO and
Shear Waves
Good reservoir
indicator is:
 P-wave bright
spot (P sensitive
to type of pore
fluid);
 At location without
S-wave bright
spot (S not
sensitive to type
of fluid).
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
9
Validating Hydrocarbon Indicators
Philosophy of Reflection Identification
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Don't necessarily assume the data polarity and
phase are what they are supposed to be.
If you are going to use synthetic seismograms,
use a suite of seismograms of various phases
and of both polarities.
If you have the ability to make comparisons in
color, do so because much more detailed
character will be visible and you will more
readily recognize polarity and phase problems.
problems.
Consider all the local character, that is, seek to
explain all the reflections in the neighborhood of
the objective.
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Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Validating Hydrocarbon Indicators
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( 1) Is the reflection from the suspected reservoir anomalous in
amplitude, probably bright?
( 2) Is the amplitude anomaly structurally consistent?
( 3) If bright, is there one reflection from the top of the reservoir and
one from the base?
( 4) Do the amplitudes of the top and base reflections vary in unison,
dimming at the same point at the limit of the reservoir?
( 5) Are the data zero phase?
( 6) Is a flat spot visible?
( 7) Is the flat spot flat or dipping consistently with gas velocity sag or
tuning?
( 8) Is the flat spot unconformable with the structure but consistent
with it?
( 9) Does the flat spot have the correct zero-phase character?
(10) Is the flat spot located at the downdip limit of brightness (or
dimness)?
(11) Is a phase change (polarity reversal) visible?
(12) Is the phase change structurally consistent and at the same level
as the flat spot?
(13) Do bright spot, dim spot, or phase change show the appropriate
zero-phase character?
(14) Is there a low-frequency shadow below the suspected reservoir?
(15) If the reservoir is thick, are there significant reflections inside?
(16) Do statistical crossplotting techniques indicate a flat spot?
(17) Is there an anomaly in moveout-derived interval velocity?
(18) Is a study of amplitude versus offset on the unstacked data likely
to yield further validation evidence?
(19) Are any shear wave data available for further validation
evidence?
Validating
Hydrocarbon
Indicators
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How many reservoirs
in this picture?
(California)
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Apply validation
criteria to each
candidate
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
10
Validating Hydrocarbon Indicators
Validating
Hydrocarbon
Indicators

How many
reservoirs in this
picture?
(California)

Apply validation
criteria to each
candidate
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Plotted without vertical exaggeration:
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three-
Dimensional Seismic Data, 4th & 6th Editions
Dimensional Seismic Data, 4th & 6th Editions
Occurrence of Hydrocarbon Indicators
Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of ThreeDimensional Seismic Data, 4th & 6th Editions
11