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8/10/2019 Seismic Interpretation by Dr. Ali Bakr
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ALI BAKR ALI BAKR ALI BAKR
SEISMIC INTERPRETATION
Dr. ALI BAKR
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1. Basic background
2. Structural Interpretation
3. Seismic attributes
4. AVO implications
5. Seismic Inversion
6. Seismic stratigraphy
7. 4D seismic (Time Laps)
Contents
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1-BASIC BACKGROUND
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• Seismic acquisition
• Seismic processing• Understanding the data
1-Basic Background
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• Seismic interpretation and subsurface mapping are key skills thatare used commonly in the oil industry
• This teaching resource introduces the basic principles of seismic
interpretation and then, if time permits, they can be applied in apractical exercise
• The resource dovetails with the A level Geology specifications
1-Basic Background
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• An air gun towed behind the surveyship transmits sound waves through thewater column and into the subsurface
• Changes in rock type or fluid contentreflect the sound waves towards thesurface
• Receivers towed behind the vesselrecord how long it takes for the soundwaves to return to the surface
• Sound waves reflected by differentboundaries arrive at different times.
• The same principles apply to onshoreacquisition
Seismic acquisition offshore
.
1-Basic Background
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Seismic acquisition onshore • Onshore seismic acquisition requires an energy input from a“thumper” truck. Geophones arrayed in a line behind thetruck record the returning seismic signal.
Sub-horizontal beds
Unconformity
Dipping beds
Geophones(receivers)
Vibrator(source)
1-Basic Background
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Seismic acquisition onshore
Lithology change
Angular unconformity
Lithology change
• Seismic horizons represent changes in density and allow the subsurfacegeology to be interpreted.
1-Basic Background
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• Wiggle trace to CDP gather
• Normal move out correction
• Stacking
• What is a reflector?
Seismic Processing
1-Basic Background
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Seismic Processing Wiggle trace to CDP gather
Graphs of intensity of sound as received bythe recorders
Graphs of intensity for one location collectedinto groups and shown in a sequence.
Wiggle traces CDP gather
1-Basic Background
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Seismic Processing
Normal move out correction
Original CDPgather …
corrected fornormal move out
21
Change in lithology from mud to sand so soundis reflected back to surface
CDP
CMPSound sources
S1 S2 S3
Data for one point from different signals to different receivers
1. More time needed to reach distant receivers so the data look likea curve.
2. Correcting for normal move out restores the curve to a nearhorizontal display.
Sound receiversR3 R2 R1
1-Basic Background
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Next, take all the sound traces forthat one placeand stack them on top of eachother
First, gather sound data for onelocation and correct for delayedarrival (normal move out)
Finally, place stacks foradjacent locations side byside to produce a seismicline
Stacking Seismic Processing
1-Basic Background
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There are many reflectors on aseismic section. Major changesin properties usually producestrong, continuous reflectors as
shown by the arrow.
A seismic reflector is a boundary betweenbeds with different properties. There maybe a change of lithology or fluid fill fromBed 1 to Bed 2. These property changescause some sound waves to be reflected
towards the surface.
Bed 1
Bed 2
lower velocity
higher velocity
energy source signal receiver
What is a reflector?
1-Basic Background
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• Common Depth Points (CDPs)
• Floating datum• Two way time (TWT)
• Time versus depth
Understanding the data
1-Basic Background
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CDPs are defined as‘the common reflectingpoint at depth on a
reflector or the halfwaypoint when a wavetravels from a source toa reflector to areceiver’.
Common midpoint above CDP
Change in lithology =reflecting horizon
Common reflecting point orcommon depth point (CDP)
Sound sourcesS1 S2 S3
Sound receiversR3 R2 R1
Common Depth Points
1-Basic Background
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The floating datum line represents travel time between the recording surface and the zeroline (generally sea level). This travel time depends on rock type, how weathered the rock is,and other factors.
The topographic elevation is the height above sea level of the surface along which theseismic data were acquired.
Floating datum
1-Basic Background
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0.25 seconds
Two way time (TWT)indicates the time requiredfor the seismic wave totravel from a source to
some point below thesurface and back up to areceiver.
In this example the TWT is
0.5 seconds.
0.25 seconds
0
0.5
TWT
s e c o n d s
surface
1-Basic Background
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0.58 sec
m
1865
926
288
926 m
• Two way time (TWT) doesnot equate directly to depth
• Depth of a specific reflector
can be determined usingboreholes
• For example, 926 m depth =0.58 sec. TWT
Time versus depth
1-Basic Background
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• Check line scale and orientation.
• Work from the top of the section, where clarity is usually best,
towards the bottom.
• Distinguish the major reflectors and geometries of seismicsequences.
1-BASIC BACKGROUND
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1-Basic Background
• Some energy will be reflected, some will betransmitted where there is a change in AI
• Amount reflected (amplitude of reflection)will depend on the relative difference inphysical properties across the interface
V11
V11
V22
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1-Basic Background
– Define reflectioncoefficient (RC)
RC = AI2 – AI1
AI2 + AI1
– If AI2 > AI1 – positive RC
– If AI2 < AI1 – negative RC
V11
V11
V22
V - V
V + V
2 2
2 2 11
11
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1-Basic Background
Polarity Conventions
Slow, Less
Dense
Fast, m ore
Dense
+veR.C.
Blue (90%)
Red (10%)
Blue (10%)
Red (90%)
Peak
(60%)
Trough
(40%)
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1-Basic Background
• Not all changes in lithology associated withchange in AI. Changes in fluid content in asingle lithology can give rise to reflections
• Different combinations of layers lithologies canhave the same RC Seismic “non-unique”
• Seismic data image interfaces – we observe
changes in AI across an interface, not propertiesof layers themselves
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1-Basic BackgroundConvolutional Theorem
Subsurface at any one location as consists of a one-dimensionalseries of reflection coefficients
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1-Basic Background
Subsurface at any one location as consists of a one-dimensionalseries of reflection coefficients
Convolutional Theorem
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1-Basic Background
Each RC gives rise to a separate reflection event, the amplitude ofwhich is proportional to the change in AI across the interface
Convolutional Theorem
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1-Basic Background
• The final image we will record for that location consists of thealgebraic sum of all the individual reflections
• Mathematically we “convolve” the wavelet with the series ofreflection coefficients
Convolutional Theorem
*
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1- Basic BackgroundData required for synthetic calculation
• Seismic Data
• Well Curves (Sonic and Density)
• Well Position relative to Seismic
• Check Shot / T-D relationship
• Well Deviation Survey
• Seismic Acquisition and Processing Info
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Impedance High Frequency
Top & Base
Resolved
Low Frequency
Top & Base
Unresolved
1-Basic BackgroundVertical Resolution
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1-Basic BackgroundVertical Resolution
30
Seismic ability to define topand bottom of a rock layer
In general, reflections are composites of thin layer effects.
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1-Basic BackgroundVertical Resolution
Resolution depends on:
Frequency content in seismic data.
The interval velocity at the objective level
f
V Dominant Wavelength of Seismic Wave =
Where: V is the velocity in unit distance per second and
f is the dominant frequency in Hz
f dom4
V R
int v ~
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1-Basic BackgroundVertical Resolution
• Most of the energy in a seismic wavelet is contained in a band offrequencies centered about the dominant frequency. The dominantperiod can be defined as the time between two major crests. Thedominant frequency is the reciprocal of the dominant period. Theequation for wavelength, , is:
= velocity/frequency
Calculate wavelengths for the following cases:
Shallow rocks: V=2000 m/s, f=50 Hz;
Deep rocks: V=6000 m/s, f=25 Hz.
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1-Basic BackgroundVertical Resolution
Conventional HFITM
Vertical Resolution – Example (‘HFI’ Processing from Geotrace )
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• Example 1:
V = 7,000 m/s
F = 50 Hz
= 7,000/50 [(m/s)/(cycles/s)]
= 140 m
1-Basic BackgroundVertical Resolution
f
V
k d
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1-Basic BackgroundVertical Resolution
• Example 2:
V = 3,000 m/s
F = 50 Hz
l = V/F
= 3,000/50 [(m/s)/(cycles/s)]
= 60 m
k d
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1-Basic BackgroundVertical Resolution (Summery)
• Vertical Resolution is the ability to detect and map thin eventssuch as reservoir sand bodies
• It is determined by the average frequency and bandwidth of the
seismic data
• We can typically resolve down to ¼ wavelength
• Wavelength is determined by frequency and velocity:
λ=V/f so resolution ~ V/(4*f)
• Resolution deteriorates with depth
1 B i B k d
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1-Basic BackgroundVertical Resolution
• The seismic signal contains a range of frequencies (left)• The broader the bandwidth, the sharper the pulse (smallerside lobes)
- 0. 5
1 B i B k d
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1-Basic BackgroundVertical Resolution
Fourier analysis may be used to see the bandwidth
of the seismic data in a given portion of the data.
• Amplitude spectrum on left shows a broad bandwidth,rich in high frequencies
• Spectrum on right is irregular and abruptly truncated atabout 45 Hz. Data were filtered post-stack as a noisereduction exercise.
1 B i B k d
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1-Basic BackgroundVertical Resolution
What is the dominant frequency of the seismic data in the intervalbetween 1500 and 1600 ms? If the velocity is 5000 m/s, what is thetuning thickness? If it is possible to detect a bed down to 1/16 ofthe wavelength, what would that be?
1 B i B k d
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1-Basic BackgroundVertical Resolution
Dominant frequency:
about 4 ½ cycles in 100 ms
= 45 cycles/second = 45 Hz
1 B i B k d
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Tuning thickness:Frequency = 45 Hz, Velocity = 5000 m/s
Wavelength = 5000/45 = 111 m
Tuning thickness = ¼ x 111 = 28 m
1-Basic BackgroundVertical Resolution
1 B i B k d
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1-Basic Background Horizontal Resolution
•
Horizontal Resolution is the ability to map lateral changes in reservoir – edges and internal structures.
• Seismic energy is reflected from a patch rather than a point. Migrationcollapses this patch and improves resolution.
• Prior to migration horizontal resolution is poor
• Horizontal resolution can approach vertical resolution if ‘aperture’ isadequate
• The wider the aperture the closer the horizontal resolution approachesthe vertical resolution
• Other seismic processes can also reduce lateral resolution
1 B i B k d
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Seismic Energy Reflects from a Patch, not a Point
1-Basic Background Horizontal Resolution Fresnel Zone
1 B i B k d
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1-Basic Background Horizontal Resolution
Lateral resolution described by Fresnel Zone
Seismic data image (“illuminate”) an area, rather than a single point
1 Ba i Ba k ou d
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1-Basic Background Horizontal Resolution
Fresnel zone diameter (F) depends upon:• Average velocity (v)
• Two-way travel time (t)
• Dominant frequency (f)F = v (t/f)1/2
1 Basic Background
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1-Basic Background Horizontal Resolution
Migration collapses diffractions and gives us horizontal resolution
To do this properly we need to record the whole diffraction
1 Basic Background
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1-Basic Background Horizontal Resolution
• Fresnel Zone example:
v = 2440 m/s
f = 25 Hz
t = 2 s
F = v (t/f)1/2
= 2440*(1/25) 1/2
= 488 m
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2- SEISMIC INTERPRETATION
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Interpretation Workflow
RegionalStudy
Review-QCData
Time/Depth/Attribute/Properties integration
Peer Review
Report
DHI/Seis. Attributes /Inversion Analysis
Reservoir PropertyMapping
Volumetric / SpatialDistribution Analysis
Structural mapping
Borehole to SurfaceSeismic Match
Seismic Horizon andFault interpretation
Velocity Modelling
Time to DepthConversion
Seismic reservoir
property mapping Geomodelling
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Basic Structural Geology Background
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Fault Classes
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Fault Classes
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Fault Classes
STRIKE-SLIP FAULT
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Fault Classes
DIP-SLIP OBLIQUE-SLIP STRIKE-SLIP
Pitch = 90 Pitch = 45”E” Pitch = 0
090
270
Fault Classes
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Fault Classes
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Fault Classes
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Fault Classes
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Fault Classes
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Fault Classes
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Fault Classes
PlannersListirc
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BASIN ANALYSIS
SUBSIDENCEL L
t
L’
T = 30 KM (CONTINENTAL)
L’ > L
T > t CRUSTAL THINING
β=L’ /L= T/ t (streching factor)
A
A
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BASIN ANALYSIS
SUBSIDENCE
SHEARING STRESS
LISTRIC FAULT MODEL
BASIN
LISTRIC FAULT
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BASIN ANALYSIS
SUBSIDENCEPLANAR FAULT MODEL
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BASIN ANALYSIS
SUBSIDENCE
BASIN RANGE
SHEARING STRESS
PLANAR FAULT
BLOCK ROTATION
BLOCK ROTATION
MODEL
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Fault Classes
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Fault Classes
Only on gravitational structures…not tectonics?
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Fault Classes
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Fault Classes
listric
or
planar
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Fault Classes
Footwall uplift
Picking faultson seismic
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Fault Classes
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Fault Classes
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Fault Classes
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Fault Classes
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Fault Classes
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Fault Classes
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Fault Classes
Fault-scarp degradation
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Fault Classes
Eroded crest
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Fault Classes
Talus at foot
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Fault Classes
Then banked in with sediment
l l
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Fault Classes
l l
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Fault Classes
F l Cl
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Fault Classes
F l Cl
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Fault Classes
F lt Cl
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Fault Classes
False fault pick
F lt Cl
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Fault Classes
F lt Cl
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Fault Classes
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V i F ld
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Various Folds
Various Folds (cont'd)
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Various Folds (cont d)
Various Folds (cont'd)
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Various Folds (cont d)
Various Folds (cont'd)
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Various Folds (cont d)
Axial plane near axis should be close to horizontal
Axis
Fault Mo e e t I di ato
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Cross section analysis
Example 1: Onlap
Syn-faulting strata
Active faulting and upliftduring deposition
Fault Movement Indicators
Fault Movement Indicators
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Fault Movement Indicators
Example 2: Offset beds ofequal thickness
Pre-faulting strata
Faulting post deposition
Fault Movement Indicators
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Fault Movement Indicators
NESW
Fault Movement Indicators
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Fault Movement Indicators
Offset onlap:1. 3R>1R2. 3R>BRR
0.5 mile
100 ms
Fault Movement Indicators
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Fault Movement Indicators
Isochore: line drawn through points of equalvertical (apparent) thickness of a unit
BRR
Calitroleum
Wilhelm
MYA4-A
McDonald
x1 x2 x3 x4 x5
1 mile
500 ms
Fault Movement Indicators
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Fault Movement Indicators
2. Thin beds
b)
c)
A’
c) filled inpaleo high(post tectonic)
b) fault belowinterval(syn tectonic)
1. Close contours
a)a) fault cut
intervalat time(syn tectonic)
Two Signatures:
Structural high
A
A ’
A’
Fault Classes
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Fault Classes
Hydrocarbon Traps
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Hydrocarbon Traps
Hydrocarbon Traps
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Hydrocarbon Traps
Fault Related
Fault Free
Hydrocarbon Traps
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Hydrocarbon Traps
Hydrocarbon Traps
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Hydrocarbon Traps
Hydrocarbon Traps
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Trap
Over flowing point or spill point Closure
height
Closure area
Pool
oil/gas column
oil/gas area
oil-water/gas-oil contact
Note: All measurements are in 3D space. All pools are in traps, but not
all traps could be pools.
Hydrocarbon Traps
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Spill point: the lowest point at which hydrocarbon may be contained in the trap. A trap may or maynot be full to the spill plane.
Closure: the vertical distance from crest (the highest point of the trap, or culmination) to spill plane. Oil-water contact (OWC): the deepest level of producible oil. Gas-oil contact (GOC) or gas-water contact (GWC): the lower limit of producible gas.
Hydrocarbon Traps
Hydrocarbon Traps
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Hydrocarbon Traps
oil
gas
trap
Height of closure
Reservoir rock
Cap rock
Spill point
pool
Height of gas
Height of oil
Basic Inversion Terminology
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gy
Modified from William 1996
Horst -Graben Inversion -Southern North Sea
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South Hewett Fault
Horst -Graben Inversion -Southern North Sea
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South Hewett Fault
Seismic Interpretation
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To Interpret:
Structure
Stratigraphy
Lithology
FracturesPressure
Pore Fluid
Predict and Characterize Subsurface Reservoirs
3D Seismic
Cube
Automated Structural Interpretation
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Automated Structural Interpretation
Ant-track
Faults
Horizons
Automated Structural Interpretation
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Automated Structural Interpretation
Combined visualisation of Dip-Azimuth and Fault Enhancementattributes.
Well 1
Well 3
Well 2
Guidance for accurate faultinterpretation
Wells are provennot to be incommunication.
Initial Check List
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• Seismic data vintage (acquisition year)?
– Acquisition report• Processing sequence, type (PSTM, PSDM, etc.)?
– Processing report• Source of data (tape, project backup) and format?
– 8-, 16-, 32-bit data? Have any AGC, Time gain filters, beenapplied? Amplitude fidelity?
• Overall data quality:– Good for structural interpretation?– Good for stratigraphic interpretation?– Good for reservoir characterization?
• Can we see fluid effects, lithology, both?• Which phase and polarity?
• Dominant frequency at reservoir level and expected resolution?• Well tie analysis?• Existing seismic picks and interpretation review (time and depth)
Initial QuestionsMigration Type?
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Time Migration Depth Migration
Migration Type?
Initial QuestionsDigitization of Geophysical Data
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Digitization of Geophysical Data
• Dynamic range:
If digital sampling ranges from 1 to 256 units of amplitude:
20log10 (256) 48 dB
The number of bits in each word determines the data dynamic
range:8-bit = 28 = 256
16-bit = 216 = 65536 20log10 (65536) 96 dB
32-bit = 232 = 4,…109 192 dB
Initial Questions Amplitude Fidelity and Filtering
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p y g
Smoothing filter, improves signal to noise ratio for interpretationpurpose, but removes discontinuities, potential faults…
Amplitude Dip guided Gaussian Filter
Initial Questions Amplitude Fidelity and Filtering
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p y g
AGC effect on data: good for interpretation and bad for attributes and
reservoir characterization
Original Amplitude AGC filter Time Gain
3D Data Load QC
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Initial QuestionsAmplitude Fidelity and Footprints
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Amplitude Fidelity and Footprints
Shallow time slice on Variance cube
Acquisition/Processing
footprints
Shallow Area ReefBuildups
0 ms
Acquisition/Processing
footprints
Shallow Area ReefBuildups
0 ms
Acquisition/Processing
fooprints
0 ms
Reefs
Initial Questions Amplitude Fidelity and Footprints
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p y p
Strong processing artifacts indicating pooramplitude fidelity
RMS Amplitude
Initial QuestionsStructural and Stratigraphic Interpretation: Good
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g p p
Initial Questions3D Data Comparison
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p
2000 Processed
Shift between the 1984 and the 2000 Surveys
1984-Processing Seismic Results
Initial QuestionsPolarity and Phase
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y
Using this convention, in a seismic section displayed with SEG normal polarity
we would expect:
• A reflecting boundary to appear as a trough in the seismic trace if Z2 > Zl
• A reflecting boundary to appear as a peak in the seismic trace if Z2 < Zl
(a) minimum- and(b) zero-phasewavelets at anacoustic-impedanceboundary with apositive reflectioncoefficient
Initial QuestionsIdeal Vertical Resolution
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Dominant Wavelength of Seismic Wave =
Where: V is the velocity in unit distance per second and
f is the dominant frequency in Hz
f
V
V(m/sec) F(Hz) /2 to /4 (m)
2000 50 20-10
3000 40 38-19
4000 30 66-33
5000 20 125-62.5
Initial QuestionsVertical Resolution and Tuning Thickness
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g
Zero phase
wavelets
T
Tuning separation
in time = 1/2 of the wavelet period
in depth = T
2
X interval velocity
Example:
If T = .020 Sec
and Vint = 6000’/Sec the tuning thickness is 60 feet
Initial QuestionsBorehole to seismic tie
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•Quality of check
shot data?
•Phase?
•Match with surface
seismic?
•Any stretch and
squeeze?
•Position of markers
versus seismic
picks?
DT RHOB AI RC WaveletTime
Review of Well TieSynthetics in time domain
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y
Review of Well TieSynthetics in time domain
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Updated well tie
New Time-Depth
Review of Well TieBorehole to 3D seismic
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Review of Well TieCheckshot Data
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Horizon 2 outlier maker
Outlier well
Do’s and Don’ts Borehole to seismic tie
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Review of Seismic InterpretationPicks in time/depth domain
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p
• Consistency between inlinesand cross-lines picks?
• Signal consistency (peak,trough, zero-crossing)
• Auto-tracking or manual, orcombination of both?
• Geological consistency(isochrone, isochore)?
Review of Seismic InterpretationPicks in time/depth domain
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Examples of inconsistencies between inlines and cross-lines
picks and impact on time grid
ick in time/depth domain
Vertical exag. 7.5x
Review of Seismic InterpretationStructural consistency
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y
• Starting from key/stronghorizons, here coal level.
• Is the interpretationstructurallymeaningful/flawless?
•Look at the fault throws andtheir vertical evolution alongfault planes
• Understand the big picturefirst
Review of Velocity Modellingand Depth Conversion
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Original stacking velocity
Well velocity (checkshots)
Evaluate the need for calibration of stacking velocity
Review of Velocity Modelingand Depth Conversion
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p
Well
Marker Depth Old Model Residual (m)
AA-1
T -2612.46 -2512.62 -99.8408
U -2727.96 -2631.32 -96.6397
V -2838.46 -2743.55 -94.9091
W -2884.56 -2791.08 -93.4754
X -2922.96 -2838.74 -84.2182
Y -3015.8 -2930.85 -84.9545
Z -3073.45 -2994.24 -79.2136
ZZ -3144.13 -3065.24 -78.8872
AB-1
T -2623.88 -2506.14 -117.745
U -2736.98 -2622.13 -114.85
V -2843.4 -2733.7 -109.695
W -2890.87 -2783.39 -107.485
X -2928.84 -2830.8 -98.0448
Y -3017.93 -2914.42 -103.508
Z -3076.67 -2980.04 -96.6268
ZZ -3148.31 -3053.87 -94.4429
•Review depthresiduals before wellcorrection is applied
• It provides a directindication of thevelocity model quality
Data Review Completed
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• Highlighted where to focus interpretation efforts and attention
(minimize valuable mouse clicks)• What data is ok to use for either further:
– Depth conversion
– Geomodeling
• Identified data that revision/update or interpretation from scratch– Go back to essentials (geology, well correlation panels,
geological environment, regional structural style, etc..
– Geology is not limited to well markers!
Geologic Correlations
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Understand well correlation first at bigpicture level guided by key/stronghorizons
Horizon Selection
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•Start with obvious and
most continuous seismicreflections detectedduring panning
•More difficult horizonsare addressed later orphantomed from keyhorizons
•Get the framework first
Structural InterpretationTraditional Fault picking
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2D on optimal section = perpendicular to fault strike
Structural InterpretationData Conditioning
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filteredinput
Data conditioning for structural interpretation
g
Structural InterpretationNoise Removal
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Edge preserving filtering – Structurally Oriented
Original Filtered Difference- =
Structural FrameworkScreening and Panning of Amplitude data
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Inlines, Xlines and Time slices
Structural FrameworkScreening and Panning of Amplitude data
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Random sections orthogonal to fault planes
Structural FrameworkScreening of Amplitude data
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Volume rendering with transparency
Structural FrameworkScreening of Amplitude data
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Volume rendering with transparency
Structural FrameworkScreening of Dip and Azimuth Volumes
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Time slice on Azimuth
Structural FrameworkScreening of Dip and Azimuth Volumes
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Time slice on Dip
Structural FrameworkScreening of Edge Enhancement Attributes
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Time slice on Variance
Interpretation- Structural Mapping
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Fault sticks
Fault markers
Interpretation- Structural Mapping
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Fault sticks
Fault markers
Interpretation- Structural Mapping
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Modeled Fault plane
Screening of Structural Framework Auto-tracking time structural map
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3D Auto-tracking will reveal data quality and
interpretation issues to be addressed eventually
•Transfer low level,repetitive tasks to theworkstation such asauto-tracking
•Maximise the valueof a mouse click!!!!
QC Your Horizon PicksIn 2D and 3D Views
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Looking for mispicks in 3D views using vertical exaggeration
1X vertical exaggeration 10X vertical exaggeration
QC Your Horizon PicksIn 2D and 3D Views
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Looking for bulls eyes and slope
anomalies on contoured maps
QC Your Horizon PicksIn 2D and 3D Views
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Pick quality and signal
consistency check on
instantaneous phase
Pick quality and signal
consistency on instantaneous
amplitude
Velocity Modeling andDepth conversion
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•Check all available data:Check shotsVSPSyntheticsStacking velocities
Geologic tops correlation
•Select, use and integrate as needed:Simple TDR from wellsAverage interval velocity
Full velocity modelling: wells + calibrated stackingEtc..
InterpretationSeismic Geomorphology
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100 m100 m
channels
Crevasse splay
TIME SLICE Y ATRIBUTOS
Stratal Slice of Amplitud Maps
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Time slice
Horizon slice
Proportional slice T W
T
Reference horizon 1
Reference horizon 2
Interpretation Summary
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• QC existing data and interpretation
– Data type, phase, resolution, amplitude, well ties, picks, etc..• Beware of noise level, noise removal to support interpretation
• Use the full 3D data and auto-tracker as much as possible
• Use 3D attributes (Dip, Azimuth, Edge Enhancement) and 3Drendering techniques (geobodies mapping, transparency) for data
screening• Minimize manual picks and clicks and maximize the use of the
workstation for repetitive low level tasks
• Ensure signal consistent horizon interpretation and geologicalconsistency before embarking on geofantasy!
• Ensure good tie with wells in time• Use and integrated all available data
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3- SEISMIC ATTRIBUTES
Seismic Attributes
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• Seismic attributes are all theinformation obtained fromseismic data, either by directmeasurements or by logic orexperienced-based reasoning.
• The main objective of theattributes is to provide detailedand accurate information to theinterpreter on structural,stratigraphic and lithologicalparameters of the seismicprospect.
Seismic Attributes
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• Pre stack:– Input data is CDP or image gathers
– Have directional (azimuth) and offset related information
– Lots of information that may not be practical in initial or basicstudies
– Contain considerable amounts of data that can be directlyrelated to fluid content and fracture orientation.
– AVO, velocities, azimuthal are the most prominent of thisclass.
• Post stack
– After data is stacked, these are computed on the trace.
Seismic Attributes
G l Cl ifi i
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General Classification
From A.R. Brown
Seismic Attributes
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Seismic attributes are specific measures of geometric, kinematic, dynamic, orstatistical features derived from seismic data. ‘General’ attributes include:
1) Reflector amplitude,
2) Reflector time3) Reflector dip and azimuth
4) Complex amplitude and frequency
5) Generalized Hilbert attributes
6) Illumination
7) Edge detection/coherence
8) Spectral decomposition
Some Important Post stack Attributes
These have a physicalas well as statisticalbasis!
Seismic Attributes
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•Envelope presence of gas (bright spots), thin-bed tuning effects,lithology changes.
•Phase lateral continuity of reflectors, bedding configurations.
•Frequency bed thickness, presence of hydrocarbons, fracture zones.
•Spectral Decomposition bed thickness.
•Coherence faults, fractures, lateral stratigraphicdiscontinuities
Why Seismic Attributes
Seismic Attributes
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• By their computational characteristics:– Instantaneous Attributes: Computed sample by sample. Trace
envelope, its derivatives, frequency and phase,… – Wavelet Attributes: Computed at peak of trace envelope and
have a direct relation to the Fourier Transform. InstantaneousFrequency
– Physical Attributes: Relate to physical qualities. Frequenciesrelate to bed thickness, magnitude of trace envelope relates toimpedance contrast.
– Geometrical Attributes: Describe spatial and temporalrelationship of all other attributes. Lateral continuity measured by semblance is a good indicator of a discontinuity. Assist in the
recognition of depositional patterns and related lithology.
Seismic Attributes
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• By their origin in the wave phenomena, we can also sub-divide the attributes into two categories:
– Reflective Attributes:
• Attributes corresponding to the characteristics ofinterfaces.
• All instantaneous and wavelet attributes can be
included under this category.• Pre-stack attributes such as AVO are also reflective
attributes,
– Transmissive Attributes
• Relate to the characteristics of a bed between twointerfaces (all physical attributes)
• Interval, RMS and average velocities, Q, absorptionand dispersion come under this category.
Attributes Interpretation
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Objectives:– Recognize an hydrocarbon anomaly or lithology
– Validate anomalies, revealing the relation rock-seismic
Methodology:
• Assume a model
• Compute or evaluate the response to the model at known locations
• Compare response of model to actual data
• Verification in new areas or intervals
Seismic Attributes
• Seismic attributes
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• Seismic attributes:
– Properties of the seismic trace when thought of as an analytic
(complex) trace with both real and imaginary parts
Hilbert transform complex trace from the Real seismic trace
Real:conventionalseismic trace
Quadrature:
imaginary partseismic trace fromHilbert transform
Seismic Attributes
I i i ib d i d f h l i i
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• Instantaneous seismic attributes are derived from the actual seismic
data• Quality of attributes is dependent on signal consistent interpretation
(grid based)
• Used as both seismic display (seismic sections), as maps (grids) andvolumes
Why do we generate Seismic Attributes ?
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•
Enhance structural and stratigraphic features for the interpreter onseismic sections
• Enhance structural and stratigraphic features on maps
• Locate misinterpretation
• Get information on lithology, facies or fluid content
• Correlate with other properties
reservoir characterisation
Display and use of Seismic Attributes
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• Seismic Amplitude:
– Trace’s amplitude value at the horizon time/depth
– Identify bright spots/dim spots
Display and use of Seismic Attributes
• Reflection Strength/Envelope:
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• Reflection Strength/Envelope:
– Total envelope of energy at any instant along the trace– High reflection strength is often associated with major change in
acoustic impedance due to lithology, fluid content (gas), orstratigraphy.
Seismic trace
Envelope
Display and use of Seismic Attributes
Q d A li d
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• Quadrature Amplitude:
– Imaginary part of the complex seismic trace– Used in conjunction with other attributes to identify
bright spots
Seismic trace
Quadrature trace
Display and use of Seismic Attributes
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• The Trace Envelope is a physical attribute and it can be used as aneffective discriminator for the following characteristics:
– Reflectivity, since mainly represents the acoustic impedance contrast
– Bright spots, possible gas accumulation,
– Sequence boundaries,
– Thin-bed tuning effects
– Major changes in depositional environment,– Spatial correlation to porosity and other lithologic variations,
– Indicates the group, rather than phase component of the seismic wavepropagation.
Display and use of Seismic Attributes
• Instantaneous Phase
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• Instantaneous Phase
– Description of the phase angle at any instant along a trace– Independent of amplitude
Expresses the degree oflateral continuity or
discontinuity of seismicreflections, pinchouts,angular unconformities,thickening and thinningzones, offlap, onlap, and
makes weak coherentreflection clearer.
Display and use of Seismic Attributes
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• Cosine of Phase:
– Cosine function applied to the instantaneous phase (+/-1)
May enhance definition ofstructural delineation
Display and use of Seismic Attributes
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• Instantaneous Frequency:– Time derivative of the phase
– Low: 0 to 1/2 of the Nyquist Frequency
Helps in correlatingreflection alongseismic section andhighlights low
frequency anomaliesbelow HCaccumulations
Display and use of Seismic Attributes
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• Apparent Polarity:– Sign of the seismic trace where reflection strength has a
local maximum value (+1 or -1)
May help distinguishdifferent kinds of brightspots (due to gas,limestone..)
Display and use of Seismic Attributes
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• Response Phase:– Calculates the instantaneous phase when the reflection
strength has its maximum
Alternate way of displayinginstantaneous attributes, lesssubject to noise sincecomputed where seismic tracehas maximum energy
Display and use of Seismic Attributes
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• Sweetness:
– Sweetness is the Envelope(Reflection Strength) dividedby the square root of theInstantaneous Frequency.
It can sometimes help indelineating subtle discontinuities
Variance
Sweetness
Display and use of Seismic Attributes
• Bump mapping:
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p pp g
– Uses illumination and shading to add another dimension to thenormal rendering of the data
This display allowsenhancing of very subtlestructural features, likesmall fault patterns
Display and use of Seismic AttributesToo many attributes…highly correlated
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Common amplitudeattributes computedin a 100ms window
Barnes, 2006
Display and use of Seismic Attributes
D i ti
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• Derivatives:
– First derivative calculates the slope of the tangent of theselected seismic amplitude (QC interpretation on zerocrossing)
– Second derivative measures the variation in the tangents of theselected seismic amplitude, directly above and below the
reflection. High values indicate rapid shift from peak totrough (short wavelength)
amplitude 1st derivative 2nd derivative
• Application of Amplitude first and second
Display and use of Seismic Attributes
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Application of Amplitude first and secondderivatives:
Second derivative can beused to help guiding thepick by providing continuityin areas of where reflectionsare poorly resolved on theraw amplitude.
Original amplitude
Second derivative
Display and use of Seismic Attributes
• Band pass filtering:
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• Band pass filtering:
Original amplitude
High pass > 25 Hz
High pass > 35 Hz
Display of Attributes Amplitude Fidelity and Filtering
AGC effect on data: good for interpretation and bad for attributes and
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g preservoir characterization
Original Amplitude AGC filter Time Gain
Display and use of Seismic Attributes
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•
Heterogeneity:• Curve length of the function within an interval for the given attribute
• Shows the heterogeneic nature of any internal reflector in a givenvolume
Low heterogeneity High heterogeneity
Display and use of Seismic AttributesLocal Attributes
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Upper Loop
Duration
Lower LoopDuration
Upper Loop
Area
Lower LoopArea
Display and use of Seismic AttributesLocal Attributes
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Seismic section crossing
high Upper Loop Areavalues
Display and use of Seismic AttributesLocal Attributes
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Upper Loop Area
Seismic Amplitude
Display and use of Seismic Attributes
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• Surface based attribute maps:– Extracted along or close to an interpreted surface
Extracted along or
close to a surface
Display and use of Seismic Attributes
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• Volume based attribute maps:– Calculated in a time/depth
window:
– Between two interpretedsurfaces
– Below/above/around aninterpreted surface
Extracted in between twosurfaces or within a constanttime window
Display and use of Seismic Attributes
• Grid based attribute
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Grid based attribute
maps:– Derived directlyfrom seismicinterpretation,independent ofseismic amplitude
data– Dip, Azimuth,
Curvature,Illumination, Edge,etc…
Dip map Carbonate Buildups, Barents Sea
Courtesy of Norsk Hydro
Seismic Attributes and Reservoir Characterisation
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• Combining attributes:
-cross-plotting of attributes against reservoir property of interestusing well data
-selection of the ones that correlate best
-statistics helps defining attribute contribution to the variance
-resultant attributes used in geostatistical kriging to interpolatethe reservoir property between wells (RAVE, LPM).
Geometric Attributes, Looking for Similarityin Seismic Data
• Geometric attributes - Stratigraphic attributes – Multi-trace
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• Geometric attributes - Stratigraphic attributes – Multi-trace
attributes
• 4 families of multi-trace attributes:– Dip/azimuth – measures reflector shape– Texture attributes– Discontinuity – measures waveform similarity– Amplitude – measure lateral changes in impedance contrast
Geometric Attributes
– Dip/azimuth – measures reflector shapeC t f t di
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• Components of vector dip
• Gradient• Curvature• Rotation
– Texture attributes• Chaos• Flatness• Divergence
• Dip Histogram• Gabor Filter bank• Volume reflection Spectral (VRS) decomposition
– Discontinuity – measures waveform similarity• Cross correlation coherence• Semblance and variance• Principal component coherence
• Principal projected gradient– Amplitude – measure lateral changes in impedance contrast
• Amplitude gradients• Cohereny energy gradients
Geometric Attributes
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Pre- and Post-Conditioning:Gaussian low-pass smoothing filter
Gaussian dip-guided filter / Layer-Parallel Smoothing
Geometric Attributes
• Pre- and Post-Conditioning:
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– Gaussian dip-guided filter / Layer-Parallel Smoothing
Amplitude Dip guided Gaussian Filter
Geometric Attributes
• Dip and Azimuth:
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Calculate localgradient
Estimate the covariancematrix of the gradient
vectors
Perform principalcomponent analysis:
Dominating orientation
PCA is a time expensive dip computation, other methods exist such as Event dip and Gradient dip
Geometric Attributes
• Dip and Azimuth:
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Dip from estimated event(0 to 90)
Dip from PCA (0 to 90)Dip from instantaneous
local gradient vector(-90 to 90)
Geometric AttributesLooking for Similarity
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Coherence AttributesExample Results
C h
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Coherencyas it is mostcommonlydisplayed;
as time-slices
C2 C3
C1
C1 – correlation
C2 – semblance
C3 – eigenstruct.
Coherence AttributesExample Results
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Coherency as it is less commonly displayed; as vertical slices
C1 C1 – correlation
Coherence AttributesExample Results
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We clearly see the effect of the vertical window…
C2 C2 – semblance
Coherence AttributesExample Results
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We clearly see the effect of the vertical window…
C3 C3 – eigenstruct.
Coherence AttributesExample Results
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We clearly see the effect of the vertical window…
3D Automated Fault Mapping Ant Tracking: Results
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Seismic ChaosVariance Ant track
Ant TrackingBiology lesson
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FoodNest
Ant TrackingBiology lesson: swarm intelligence
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FoodNest
Ant TrackingBiology lesson: swarm intelligence
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FoodNest
Conclusion:“Dumb” ants do smart things!
Automated Fault Mapping Ant Tracking
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Seismic
Fault AttributeAnt Track Cube
Ant Track FaultsFault System Analysis
Fault Attribute vs. Ant Tracking
Time slice
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Ant trackVariance
Geometric Attributes
• Dip/azimuth – measure reflector orientation
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• Partial derivatives of Dip enable to compute curvature (change ofdip as a function of azimuth)
• 2D Curvature:
Curvature calculated along picked horizons
1. pick horizon2. smooth horizon3. calculate curvature on tight grid for short wavelength estimates4. smooth horizon some more5. calculate curvature on coarse grid for long wavelength estimates
Curvature Attributes
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Courtesy of Bruce Hart, McGill Univ.
Definition of curvature Second-order derivative of
curve
Curvature describes howbent a curve is at a particularpoint on the curve
( Roberts, 2001 )
2D Curvature Attributes
Drainage system onbasement
Basement faults
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CurvZ: Negative Curvature (Concave up)(short length filter)
Deep Canyons related todrainage system
N-S trend ofdistinctive scarpand dip slopes
geomorphologySinkhole
basement
Courtesy of Bruce Hart, McGill Univ.
Variance
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Time slice at 680ms
3D Mean Curvature
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Time slice at 680ms
3D Maximum Curvature
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Time slice at 680ms
3D Minimum Curvature
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Time slice at 680ms
Seismic Attributes
Some Important Post stack Attributes (Volume Attributes)
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• Post-stacked attributes ( i.e. not AVO or Velocity) can be calculated as a volume, as aslice, in a time window, or along a horizon .
– The volume can be displayed and interpreted like any other cube of data…however most interpretation packages include the ability to transform the data byslice
– The window can be a constant flat time interval, hung from a structurallyinterpreted horizon or between two horizons
– Horizon attributes are normally calculated and extracted from a data volumefollowing automatic spatial tracking or snapping.
• Time derived attributes are very helpful for checking your interpretation. If you useauto-tracking a lot then this step is especially important.
• While most horizon attributes are from near the structural top of the reservoir do notforget that attributes from below the reservoir can also give you valuable information -i.e. the gas shadow zone
Instantaneous Attributes
Seismic Attributes
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• When considered as an analytical signal a seismic trace can be expressed as acomplex function such as u(t)=x(t)+iy(t) where x(t) is the recorded trace itselfand y(t) is its quadrature (a 90 degree phase-shifted version of the recordedtrace).
• There are 3 instantaneous attributes
– Amplitude which is proportional to the square root of the of the total
energy of the signal at an instant in time and is used to identify brightand dim spots.
– Phase which is a measure of continuity and is used to delineate featuressuch as pinchouts, onlaps, and prograding reflectors.
– Frequency which is the time rate of change of instantaneous phase andcan help identify condensate and gas reservoirs, which tend to attenuatehigh frequencies
Instantaneous Attributes
Seismic Attributes
Input Trace with envelope
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Input Trace with envelope
Quadrature trace with envelope
Instantaneous Phase
Instantaneous Frequency
Envelope attribute also calledinstantaneous amplitude orreflection strength Frequency
Seismic Attributes
Instantaneous Attributes
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• Four “principal” volumePost Stack attributes.
• Reflection strength,instantaneous phase andinstantaneous frequency are“complex-trace” attributes
Seismic Attributes
Instantaneous Amplitude
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• Amplitude provides information on : – Sediments and their fluids by virtue of their velocity density contrst.
– Amplitude change suggest changes in the nature of rocks and fluids (oil,gasand water).
– Commonly used amplitude based indicators, in hydrocarbon industryindustry , are Bright spots, Dim spots, and Flat spots.
Not all hydrocarbon accumulations produce detectable amplitude changes.Not all changes in seismic amplitude are associated with changes in fluid saturation.Changes in lithology, bed thickness, porosity and other factors can cause changes inseismic amplitude.It only takes a small amount of gas to generate an impressive looking bright spot;not all are associated with commercial accumulations of hydrocarbon. Conformitybetween structure contours and the limits of a high-amplitude area is oftenconsidered to be an indication that the amplitudes are related to the presence ofhydrocarbons (a bright spot).However, this correspondence will only be observed if:
the sand is continuous (not compartmentalized by stratigraphic or structuralfeatures),there are no hydrodynamic factors that tilt the fluid contact.
Seismic Attributes
Instantaneous Amplitude
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• Amplitude provides information on :
– Sediments and their fluids by virtue of their velocity density contrst.
– Amplitude change suggest changes in the nature of rocks and fluids (oil,gasand water).
– Commonly used amplitude based indicators, in hydrocarbon industryindustry , are Bright spots, Dim spots, and Flat spots.
• Not all hydrocarbon accumulations produce detectable amplitude changes.Not all changes in seismic amplitude are associated with changes in fluidsaturation. Changes in lithology, bed thickness, porosity and other factorscan cause changes in seismic amplitude.
Seismic Attributes
Instantaneous Amplitude
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• Bright spot : It is associated with strong amplitude contrastacross lithologies and their fluid (oil, gas and water) content.
• Dim spot: It is associated with weak amplitude contrast acrosslithologies and their fluid (oil, gas and water) content.
• Flat spot: Associated with fluid contact.
Seismic Attributes
Instantaneous Phase
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• It is phase independent ofamplitude, and its valuesare in degrees and rangefrom +180 to -180. Becauseinstantaneous phase
contains no amplitudeinformation, it iscommonly used to examinereflection (i.e.,stratigraphic) continuity;changes in amplitude alonga reflection can sometimesgive the impression oflateral discontinuity.
Dr ALI BAKR
Seismic Attributes
Instantaneous Frequency
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• Instantaneous frequency is therate of change of phase. Itsvalues are in cycles/second(Hertz).
• Instantaneous frequency is
useful for detecting tuningeffects (although peak frequencyoccurs at a different thicknessthan for tuning of seismicamplitude), fractures, gas (seenext slide) and other features.
Seismic Attributes
Instantaneous Frequency
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Can be used to detect gas however is not really reliable because ittends to be noisy
• Arc Length
– total length of the seismic trace over a time window– increase in amplitude gives more trace length as well as
oscillation caused by increased frequency hence is really acomposite of amplitude and frequency
– can be used to map depositional facies
OGCI - SER - Attributes
Intro thru Horizon ... -
232
Seismic Attributes
Amplitude-Bright Spot
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Gas SS
Bright Spot
The Sag
Not all Bright Spot prospects are as obvious as this simple model,but the idea is the same, and most are as subtle as a migraine.
Seismic Attributes
Amplitude-Dim Spot
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Frequently, an increasein porosity, > 0,perhaps accompanied bya pore fluid change tohydrocarbons, leads to adecrease in theimpedance of an
otherwise highimpedance rock – suchas a carbonate or olderSS.
V (low )
V (high
)
Dim SpotNote the high amplitudeexit event - with a timesag caused by the lower
velocity in the porouszone
Seismic Attributes
Amplitude-Dim Spot
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Generalized curves showing how theacoustic impedances of gas sand, watersand and shales increase with depth.
Bright spot occurs above depth A, where islarge contrast in and gas-sand impedancesbut a modest difference between shale andwater –sand impedances.
Polarity reversals occur between depths Aand B, where water –sand impedance isgreater than shale impedance but gas-sandimpedance is less than shale impedance.
Dim spot occur below depth B, where thethree impedance curves converge and there
are only samll impedance contrastsbetween shale and either type of sand,brine-filled or gas –filled.
Seismic Attributes
Amplitude-Flat Spot
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Old and venerable, theflat spot, resulting
from gas-water contactreflections, is still
widely used inexploration anddevelopment.
Salt
GasWater
Z
T
Z
Note that the flat spot is
tilted on the time section.
Why?
The flat spot has regained it
flaticity when converted to depth.
Seismic Attributes
Amplitude-Flat Spot
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3-Seismic Attributes
Amplitude-Flat Spot
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Modified from Brown, 1996
Seismic Attributes
Data specification needed for Attributes
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• For 8-bit data, amplitudes theoretically range from ±128,16-bit data theoretically range from ± 32,768 and 32-bitdata range from ± 4,294,967,296. 32- and 16-bit data havemore dynamic range than 8-bit data, but take up
correspondingly more amounts of storage space.
• You should work with 16- or 32-bit data when doingquantitative attribute analyses.
Seismic Attributes
Attributes Combination
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• Attributes may be combined with each other
– E.g., amplitude-weighted phase
• This helps to combine their effects
• Although simple linear correlations between a physical propertyand an attribute are sometimes found, relationships are moreoften non-linear (e.g., Hart and Chen, 2004) and more than one
attribute is needed predict the physical property of interest
Seismic Attributes
Attributes Combination
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CoherencyAmplitude
Amplitude Coherency
Multiplying coherency(semblance) by amplitude makesstructural and stratigraphicfeatures more distinctive - in this
case fault arrays and meanderingturbidities channels[Shiehallion].
Seismic Attributes
Horizon Attributes
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1. Identify horizon of interest2. Pick horizon on a selected grid of lines3. Pick all intermediate traces using an automatic picking
algorithm4. Extract horizon attributes:
• Time• Amplitude• Dip• Azimuth• Combined dip/azimuth
Seismic Attributes
Horizon Attributes
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Seismic Attributes
Horizon Attributes
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Dip & Azimuth• Dip/azimuth cubes only show relative changes in dip and azimuth, since
we do not in general have an accurate time to depth conversion
• Dip/azimuth estimated using a vertical window in general provide more
robust estimates than those based on picked horizons
• Dip/azimuth volumes form the basis for volumetric curvature, coherence,and structurally-oriented filtering
• Dip/azimuth will be one of the key components for future computer-
aided 3-D seismic stratigraphy
Seismic Attributes
Horizon Attributes
A h(Rijks and Jauffred, 1991)
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Dip& Azimuth
Time Dip Azimuth
Seismic Attributes
Horizon Attributes
i A li d E i (Rijk d J ff d 1991)
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Horizon Amplitude Extraction (Rijks and Jauffred, 1991)
top
0.8
base
1.0
0.9
t ( s )
1 km
2 km
Seismic Attributes
Horizon AttributesA li d K d H i S
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Amplitude Keyed to a Horizon or Sequence
Seismic Attributes
Attributes Extractions
U d t d th l it f d t If t it t h
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• Understand the polarity of your data. If necessary, convert it to zero phase.
• Tie expected reservoir response from logs to seismic.
• Pick top and bottom of reservoir using autotracking of peaks and troughs.
• Picking the top of a stratigraphic unit is usually more indicative of the sequence than the bottom.
• Composite amplitude partially compensates for adjacent acoustic impedances adjacent to the topand bottom of the reservoir by ‘stacking’ the absolute value of the reflectivity at the topand bottom.
• Be sure to annotate your amplitude extractions!• Polarity
• Offset above or below picked horizon• Measure (e.g. composite, top, bottom, average absolute value, etc)• Window length (if any)
Seismic Attributes
Coherency Attribute
A f t t t i il it f th i i f
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A measure of trace to trace similarity of the seismic wavformwithin a samll analysis window.
inline inline
Coherence compares the waveforms of neighboring traces
Seismic Attributes
Coherency AttributeWhy we use Coherency
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• Excellent tool for delineating geological boundaries (faults,lateral stratigraphic contacts, etc).
• Allows accelerated evaluation of larg data sets.
• Provided quantitative estimate of fault /fracture presence.
• Often enhance stratigraphic information
Seismic Attributes
Coherency AttributeCoherency data volume
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Seismic Attributes
Coherency AttributeCoherency data volume
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Coherence Time Slice
Seismic Time Slice
Seismic Attributes
Coherency AttributesCoherency data volume
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Coherence Time Slice
Seismic Time Slice
Seismic Attributes
Horizon Slice
AdvantagesDi ad a ta e
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• Focuses on reservoir or otherzone of interest
• Illuminates depositionalenvironment at a fixed geologictime
• Avoids low coherence “structuralleakage” due to steep dip
• Steers coherence calculationalong an interpreter-defineddip/azimuth, resulting in
generally sharper contact images
Disadvantages• Analysis limited to only a few
discreet horizons, which aretime consuming to pick
• Analysis limited to the extent
of the interpreted horizon• Picking errors can bias the
result or create artifacts
• Some geological surfacessimply cannot be characterized
by peaks, troughs, or zerocrossings
Seismic Attributes
Time Slice
Advantages Disadvantages
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Advantages• Focuses on reservoir or other
zone of interest
• Illuminates depositionalenvironment at a fixed geologic
time• Avoids low coherence “structuralleakage” due to steep dip
• Steers coherence calculationalong an interpreter-defineddip/azimuth, resulting in
generally sharper contact images
Disadvantages
• Analysis limited to only a fewdiscreet horizons, which aretime consuming to pick
• Analysis limited to the extentof the interpreted horizon
• Picking errors can bias theresult or create artifacts
• Some geological surfacessimply cannot be characterizedby peaks, troughs, or zerocrossings
Seismic Attributes
Coherence volumes
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Coherence on a time slice Coherence along structure
Seismic Attributes
Spectral Decomposition
Uses the dis rete Fourier transform to
x y
z
I
3-D Seismic Volume
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Uses the discrete Fourier transform to:
• quantify thin-bed interference,and
• detect subtle discontinuities.
x y
z
x yz
x y
freq
x y
freq
Interpret
Subset
Compute
Animate
Interpreted3-D Seismic Volume
Zone-of-InterestSubvolume
Zone-of-InterestTuning Cube
(cross-section view)
Frequency Slicesthrough Tuning Cube
(plan view)
Seismic Attributes
Spectral Decompositionx
y
z
I
3-D Seismic Volume
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x y
z
x yz
x y
freq
x y
freq
Interpret
Subset
Compute
Animate
Interpreted3-D Seismic Volume
Zone-of-InterestSubvolume
Zone-of-InterestTuning Cube
(cross-section view)
Frequency Slicesthrough Tuning Cube
(plan view)
Multiply
Tuning Cube
x y
freq
x y
freqx
y
freqx
y
freq
Seismic Wavelet Noise Thin Bed Interference +
Add
Seismic Attributes
Spectral Decomposition
y
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xy
freq
xy
xy
xy
xy
xy
xy
xy
xy
xy
xy
xy
freq
Split Spectral Tuning Cubeinto Discrete Frequencies
Tuning Cube
Spectrally BalancedTuning Cube
Gather Discrete Frequencies
into Tuning Cube
Independently NormalizeEach Frequency Map
Frequency 1 Frequency 2 Frequency 3 Frequency 4 Frequency n
Frequency 1 Frequency 2 Frequency 3 Frequency 4 Frequency n
Frequency Slicesthrough Tuning Cube
(plan view)
Spectrally BalancedFrequency Slices
through Tuning Cube(plan view)
Seismic Attributes
Spectral Decomposition
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Spectral DecompositionReal Data ExampleOffshore Africa
spectral decomposition
80ms analysis window
centred 80ms above
a picked horizon
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hrz - 040ms
hrz - 120ms
a picked horizon
Red = 60hz amplitude
Green = 50hz amplitude
Blue = 40hz amplitude
Courtesy of Lantz, Aluvihare and Partyk
spectral decomposition
80ms analysis window
centred 40ms above
a picked horizon
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a picked horizon
Red = 60hz amplitude
Green = 50hz amplitude
Blue = 40hz amplitude
hrz - 000ms
hrz - 080ms
Courtesy of Lantz, Aluvihare and Partyk
spectral decomposition
60hz amplitudeanalysis window = 80ms
Centred:
80ms above the picked hrz
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80ms above the picked hrz40ms above the picked hrz
00ms above the picked hrz
youngest oldest
higher lower
hrz
Red
Green
Blue
Courtesy of Lantz, Aluvihare and Partyk
Seismic Attributes
Spectral Decomposition
Real Data Example
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Real Data ExampleGulf of Mexico , Pleistocene age equivalentOf modern day Mississippi River Delta
Seismic Attributes
Channel “A”
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Gulf of Mexico Example 10,000 ft
Channel “B”
Fault-Controlled Channel
Point Bar
N
1
0
Amplitude
analysis window length = 100ms
Seismic Attributes
Channel “A”
F lt C t ll d Ch l
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Gulf of Mexico Example 10,000 ft
Channel “B”
Fault-Controlled Channel
Point Bar
N
1
0
Amplitude
analysis window length = 100ms
Seismic Attributes
Channel “A”
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Gulf of Mexico Example 10,000 ft
North-South Extent
of Channel “A” Delineation
Channel “B”
Fault-Controlled Channel
Point Bar
N
1
0
Amplitude
analysis window length = 100ms
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4- AVO
Factors Affecting Amplitudes
Superimpose
d Noise
Instrument Balance
Geophone
Sensitivity &Coupling
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Coupling
SourceStrength,Coupling andDirectivity
Spherical
divergence
Variation ofReflectionCoefficient with
Incident Angle
Reflector Curvatureand rugosity
Interference ofdifferent Events
Absorption
Array Directivity
ScatteringPeg-Leg multiplesfrom thin reflectors
Reflectioncoefficient
AVO
AVO definition
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The variation in the amplitude of a seismic reflection with
source-geophone distance. Depends on the velocity, density
and Poisson ratio contrast. Used as a hydrocarbon
indicator for gas because a large change in Poisson’s ratio
(as may occur when the pore fluid is a gas) tends to produce
an increase in amplitude with offset.
4-AVO
AVO Assumptions
AVO A ti
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•AVO Assumption
•No seismic attenuation
•No transmission loss
•No wavelet interference (tuning)
•Amplitude vs angle(
)
•Large angles
•Pre-stack events flattened
•Seismic Processing
•Q compensation
•Gain function
•Broad amplitude spectrum
•Remove wavelet•Zero-phase data
•Pre-stack migration
•Map offset to angle,
•Avoid offset mute
•Accurate (high-order) NMOcorrection
4-AVO Implications
• Amplitude Versus Offset is a
AVO definition
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Amplitude Versus Offset is achange of reflectivity withOffset across a CMP gather.
• It is determined by the P-wave,
S-wave and density contrast atthe interface
• For clastic rocks, theseparameters are dictated byphysical properties such as
porosity, fluid and lithology.
4-AVO Implications
AVO principles
• Seismic waves are reflected
at a boundary between Layer 1
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a a bou da y be eedifferent rocks
• At normal incidence,the reflected wave
has an amplitude R :
• R = 0.1 is a BIG reflection !
incident
1
reflected
R
transmitted
T
R
Z Z
Z Z
2 1
2 1
Z V
density wavespeed
i i i
Layer 2
4-AVO Implications
AVO principles
At fl ti i l d ti P
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At every reflection in land section - P-waves that are not exactly at right-anglesto a reflector partially convert into S-waves which continue on down the
section reflecting and refracting.
AVO: is due to partitioning ofthe sound energy at interface
• The AVO technique for DHI is based on two principles:
AVO principles
4-AVO Implications
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• The AVO technique for DHI is based on two principles:
1. When Gas replaces brine in reservoir rocks, Poisson’sRatio (Vp/Vs) Decreases.
2. When Poisson’s ratio decreases, Rc and amplitudebecomes more negative with increasing angle.
4-AVO Implications
AVO /AVA principles
• Change in Incident Angle ->Change in Amplitude
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g gChange in Amplitude
• Different Offsets, Same Time ->Different Incident Angles ->Different Amplitudes
• Same Offset, Different Times ->
Different Incident Angles ->Different Amplitudes
• Amplitude changes with OffsetAND Time
• Temporal & Spatial change in
velocity complicates theproceedings!
4-AVO Implications
AVO /AVA principles
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Angle of incidence decreases with depth for constantoffset trace
Angle of incidence constant for all depths on a constant
angle trace.
Water
G E C O L O N G V A
O S L O
4-AVO Implications
P-wave & S-Wave
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incident
P wave
reflected
P wave
WaterVp = 1500m/s
Vs = 0m/s
Hard Sea-bedVp = 2500m/sVs = 1200m/s
transmitted
P wavetransmitted
S wave
4-AVO Implications
• P Wave Velocity Measured :
AVO Parameters
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• P-Wave Velocity - Measured :
– Well logs
– Seismic Velocity Analysis• Density - Measured :
– Well logs– Empirically from P-Wave Velocity
• S-Wave Velocity - Difficult to Measure
– P-Wave velocity/S-Wave velocity Ratio
– Poisson's Ratio (Rock Property)– Multi-component data analysis
4-AVO Implications
AVO principles
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4-AVO Implications
AVO principles
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4-AVO Implications
AVO principles
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4-AVO Implications
Modulus = Stiffness(Stress/Strain Ratio)
Bulk Modulus κ (incompressibility)
Bulk modulus – measure ofcompressibility of rocks and fluids
Change in volume, not in shape
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Dr ALI BAKR
Bulk Modulus κ (incompressibility)Response to Compressive Stress
Change in Pressure
Relative Change in Volume
Shear Modulus μ (rigidity)Response to Shear Stress
Change in Shear Force per unit area
Relative Displacement
Shear modulus – measurereluctance to change shape
Change in shape, not in volume
4-AVO Implications
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3/4 P V
S V
4-AVO Implications
• At any point in the sub-surface, there are only three independentacoustic rock properties responsible for seismic reflection :
– Vp,
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– Vs,
– density
• All attributes we compute will depend on the the spatial distribution
of the above three properties.• From these attributes we would like to infer:
– Rock Properties
– Fluid type
– Porosity/Permeability
– Pressure
4-AVO Implications
AVO principles
Poisson's ratio
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Poisson's ratio is simply a measure of how much thecross-section of a rod changes when it is stretched. In afluid, doubling the length halves the width (the volumeis retained) which yields a Poisson's ratio of 0.5. A rod
which never got any thinner, regardless of the amount ofstretching applied, would have a Poisson's ratio ofzero. There is a simple relationship between the P-wavevelocity, the S-wave velocity and Poisson's ratio...
4-AVO Implications
DL
DW
Relative Change in Width
σ =
AVO principles Poisson’ ratio
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2
2
/1
/5.0
P S
P S
V V V V
Dr ALI BAKR
gRelative Change in Length
Poisson’s ratio is related to VP /VS ratio:
5.0
1
/ S P V V
σ
Poisson`s Ratio σ
4-AVO Implications
Poisson’s Ratio varies :
may be thought of as a measure of Incompressibility
AVO principles Poisson’ ratio
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= .1= .4 = .3
may be thought of as a measure of Incompressibility
Wet Sand Oil Sand Gas Sand
0.00.5
4-AVO Implications
AVO principles Poisson’ ratio
Th h d l f k d t h h
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• The shear modulus of a rock does not change whenthe fluid is changed.
• However, the bulk modulus changes significantly
when the fluid changes.• As such, the p-wave velocity of a rock will change ashydrocarbon saturation changes whereas the s-wavevelocity will change relatively little (there is a slightdensity effect).
4-AVO Implications
AVO principles
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In basins where the geologic section is relatively young and unconsolidated-ater oil and/or gas response may be seen in amplitude studies DHI’
4-AVO Implications
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water, oil, and/or gas response may be seen in amplitude studies-DHI’s.
• Gas or light oil can significantly decrease the Acoustic Impedance ofa porous zone versus a brine fill.
• The anomalous amplitude should conform to a trap configuration.
• The hydrocarbon-water contact may occur as a flat reflection.
• Area and thickness of a seismic hydrocarbon anomaly may be used
for pre-drill volumetric estimates
I II III IV
4-AVO Implications
AVO Classes
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I II III IV
Top ofReservo
ir
Far Near F N F N F NOffsets
4-AVO Implications
Class 1 events areencountered in
high impedance reservoirs.The
AVO Classes
1
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TheAVO behavior is a peakthat dims.
Class 2 events are encountered innear zero impedance reservoirs.
The AVO behavior is a weak peakor trough that brightens to astronger trough at far offsets orincident angles.
Class 3 events are encounteredin low impedance reservoirs.The AVO behavior is a troughthat brightens at far offsets orincident angles.
IncidenceAngle (offset)
Class 2
R e f l e c t i o n
C o e f f i c i e n
t
Low Impedance Reservoirs
C l a s s 3
High Impedance Reservoirs
C l a s s 1
Dimming
Brightening
Dimming
Brightening
4-AVO Implications
AVO Classes
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4-AVO Implications
AVO Attributes
If we measure the amplitude of each reflection amplitude as a function ofoffset, and plot them on a graph as a function of the sine of angle of incidence
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, p g p gsquared, weobserve a straight line. For any line, the intercept and gradient can bemeasured. By linearzing the complicated mathematics behind the AVOtechnique, Richards and Frasier (1976) and Wiggins et al (1986) gave us the
following physical interpretation of the intercept and gradient:
Intercept A = the P-wave reflection amplitude.
Gradient B = the P-wave reflection amplitude minus twice the S- wave reflection amplitude.
4-AVO Implications
AVO Attributes
When you plot the amplitude of the signalfor a reflector (i.e., horizon) against the offset
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of the trace (or the calculated angle that thecorresponding sound wave would makewhen it met the reflector), the plot yields the"Intercept", where the trend of the amplitude
measurements meets the zero-offset line (soit would be equivalent to a geophone directlynext to the source, and a 90° angle to thereflector). It also yields the "Gradient", whichis the slope of the curve made by the plotpoints. The sums or differences of these
gradients and intercept values can then beused for mapping AVO anomalies. A
B
4-AVO Implications
AVO Attributes
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Common Angle ofincidence calculatedfrom smoothed
stacking velocities
4-AVO Implications
AVO Attributes
R() P + G sin2
Angle
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Intercept Gradienttrace trace
slope = G
( ) G si
sin2
ObservedLinear Fit
P
intercept
4-AVO Implications
AVO Attributes
Using the values for VP, VS, and density ρ shown in last
Figure , we can now work out the values for the AVOintercept and gradient for the wet and gas sands. For the wetsand, the VP/VS ratio in both the sand and shale layer is
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sand, the VP/VS ratio in both the sand and shale layer isequal to 2. As shown in this leads to the simplification that B= −A for both the top and base of the layer.Using the parameters shown in the figure gives: ATOP_WET= BBASE_WET = +0.1 and ABASE_WET =B TOP_WET = -0.1.For the gas sand, the VP/VS ratio is equal to 1.65, and theintercept does not simplify as it did the wet sand.
However, the calculation is still straightforward, and leads toATOP_GAS = BTOP_GAS = -0.1 and ABASE_GAS =BBASE_GAS = +0.1. Note that, for the gas case, A=B for boththe top and base of the layer.The AVO curves for the wet and gas cases are shown in figure4, for an angular aperture of 0º to 30º. It is observed that theabsolute values of the gas sand curves show an increase inamplitude, whereas the absolute values of the wet sandcurves show a decrease in amplitude. These values do fall
within a reasonable petrophysical range for class 3 anomalies.
4-AVO Implications
AVO Attributes
After scaling each of the values of A and B by a factor of 10 (to give values of +1 and -1) they
have been put on an A-B cross plot, as shown in Figure 5. In our example, the wet points(shown as solid blue circles) establish the wet sand-shale trend, and the top and base gas
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, p g(shown as solid red circles) plot in the other two quadrants of the A-B crossplot. This is atypical class 3 AVO anomaly (Rutherford and Williams, 1989), caused by gas saturationreducing the sand impedance and the Vp/Vs ratio of the sand encased in the shale.
4-AVO Implications
AVO Attributes
•When we introduce gas into a sandstone, VP decreases whereas VS increases slightly
W ill th t thi d i VP/VS ti h i l ti lit d th t
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•We will see that this decrease in VP/VS ratio causes a change in relative amplitude thatwill vary with angle of incidence.
•By analyzing this variation in amplitude we will try to extract some lithologicalinformation from the data
•Poisson’s Ratio is a useful number to know as it may be a direct hydrocarbon indicator(DHI)
•S-Waves do not travel in water – they are converted back to P-Waves at the waterboundary
•S-waves are less affected by gas than P-waves
4-AVO Implications
AVO AttributesSeismic Gather
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A m p l i t u d e
sin2q
A
B
Offset
t
4-AVO Implications
AVO Attributes
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Full Stack
A
m p l i t u d e
sin2q
A(Y Intercept)
B (Slope)
Compressional Impedance Reflectivity
AVO Gradient Section
AVO Gradient Section
4-AVO Implications
AVO Attributes
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Full Stack
A m p l i t u d e
sin2q
A (Y Intercept)
B(Slope)
Far Offset Stack
Far Offset Stack
Near offset Stack
4-AVO Implications
AVO Attributes
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Full Stack
A m p l i t u d
e
sin2q
A (Y Intercept)
B (Slope)
Far Offset Stack
Far Offset Stack
Near offset Stack
4-AVO Implications
Myth• AVO does not work
G d li d i
Reality• AVO does work under the right
circumstances
AVO Misconceptions
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• Gas-sand amplitude increaseswith offset
• AVO can not be used to detect oilsands
• AVO does not work incarbonates• Land AVO is more difficult than
marine AVO• Vp/Vs is 1.6 for brine sands, 1.8
for dolomites, 1.9 for limestones,and 2 for shales
• Rp and Rs are readily extractedfrom R(0)
circumstances• Gas-sand reflection coefficients
generally become more negativewith increasing of offset.
• High GOR light oil-saturatedrocks may exibit significant AVOanomalies
• There are some applications• The marine short-period
multiples are still a problem• Vp/Vs varies significantly
• Rp and Rs can be extracted fromR(0) and G if Vp/Vs is kbown
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5. SEISMIC INVERSION
Inversion vs Modeling
SyntheticLogs
Wavelet
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Impedance Seismic
Wavelet
Post-Stack Inversion
Gt
Low impedance zone is interpreted as higher porosity
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ICI Horizontal Georgetown Field
Gtn
Post-Stack Inversion
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Patch Reefs in the Edwards?
Post-Stack Inversion
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Interpreting an acoustic impedance inversion forlithology, porosity and fluids is simular tointerpreting a sonic log without the use of any
other logs. Why do it if there is more information?
Post-Stack Inversion
Post-Stack Inversion
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Glen Rose Reef
Terminology and Background
Acoustic Impedance = Velocity X Density
Vp = Velocity of Compressional waveVs = Velocity of Shear wave
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-Acoustic Impedance Inversion is a technique for measuring the
Impedance of the Earth’s sub-surface layers from seismic data
Vp/Vs ~ Poisson’s ratio
-Using Shear and Compressional Velocities, we can estimatePhysical rock properties from seismic data
Benefits of 3D Inversion
• Lithology and Fluid Discrimination
• Used for Reservoir Property Prediction
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• Best Tool for Reservoir Characterization
• Best Method for Optimized Field Development
• Increased Reflectivity in Shear Volume
• Calibration to Well Data and Rock Properties
• Increased Signal Bandwidth
• Easier to Interpret
Rock Property Calibration
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GWC
Top Reservoir
Laminated Pay
Rock Property Summary
• From well calibrations, seismic derived attributes can be used todiscriminate between the following rock/fluid classes:
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• Clean Gas Sands Low Pwave Impedance, Low Vp/VsRatio
• Clean Water Sands High Pwave Impedance, IntermediateVp/Vs Ratio
• Laminated Gas Sands Reduced Pwave Impedance andVp/Vs Ratio
• Shales Increased Pwave Impedance,Intermediate to higher Vp/Vs Ratio
Deliverables
• Acoustic Impedance Volume (Product of Velocity and Density)
– Porosity, Geometry and Lithology• Shear Impedance VolumeLithology Fluid
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– Lithology, Fluid
• Density Volume– Fluid type and ‘fizz water’ discriminator
• Vp/Vs Volume or• Poisson’s Ratio Volume – Lithology, Fluid type, Net/Gross ratio’s
• Porosity Volume
• N/G and Sw Estimations
Avo Analysis – Obtaining Shear Velocity estimates
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Rock Property Calibration
Sh V l it
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Shear Velocity
Pwave Velocity
Easier to Interpret
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Inversion Workflow
Vp/Vs
Model
AVO Analysis and
Processing
Pre-Stack Full
WaveformInversion
Rock Physics
Analysis andModeling
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LowFrequencyModels
Petro-Acoustic Calibration
P,S, Absolute Impedance & Density
Volumes
IRDIntegratedReservoirDescription
P, S, Density Reflectivity Volumes
Quality Control of Inversion Process
• Well logs should be examined for suitable relationships between
measured impedance logs (calculated by dividing the density bythe the sonic log) and properties such as porosity and fluid type
• Well Logs should be converted to time and edited for borehole
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• Well Logs should be converted to time and edited for boreholeeffects, balanced, and classified based upon quality
• Synthetics should be generated for all wells. Logs that do not tie
should be investigated for problems in log, wavelet, or seismic• It is generally preferable to run a loosely constrained trace based
inversion first (possibly augmented by non seismic data such astrend data from velocities or wells) to use for interpretation of amore tightly constrained model for later use in a model based
inversion
Dr ALI BAKRAfter R. B. Latimer
Quality Control of Inversion Process
• The main test of inversion accuracy is how well it ties to the input
data• Volumes that rely heavily on log derived models should matchthe logs at the well locations
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the logs at the well locations
• More model based volumes should match the seismic and thesynthetic created after inversion
• To make a valid comparison between log data and invertedimpedance the log data should be filtered t o the range of theseismic frequencies
• In all cases a universal check is to compare the model to well datathat was not included in the processing - a “blind” accuracy test
Dr ALI BAKRAfter R. B. Latimer
Quality Control of Inversion Process
If results of the inversion do not tie and you have correctly processed
logs then check the wavelet• an inversion should be done over a time target with a waveletextracted from that interval
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extracted from that interval
• if a wavelet from deeper is used it may have too low of frequencyand can result in “ringing”
• if a higher frequency wavelet from a shallower interval is useddeeper than results will appear smeared
• wavelets with an incorrect phase or amplitude spectrum can resultin erroneous time shifts that contain extra side lobes an createfalse geological features
Dr ALI BAKRAfter R. B. Latimer
Quality Control of Inversion Process
• Lack of low frequency can also be a problem. Sources other thanlogs include pre-stack time or depth migration velocities
• The final AI product should also be checked against a relativeimpedance result (low frequencies have been filtered out) While
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impedance result (low frequencies have been filtered out). Whilethis model is limited structurally and stratigraphically … anyfeature that is only seen on the broadband volume but notapparent on the band-limited target should be carefully examined.It could be the result of a poorly implemented low frequencymodel.
Dr ALI BAKRAfter R. B. Latimer
A Question of Scale
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Dr ALI BAKR
Question of Heterogeneous Reservoirs
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Dr ALI BAKR
Establishing a Relationship Between AI and Lithology
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Dr ALI BAKRFrom C. Torres-Verdin et al
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6-SEISMIC STRATIGRAPHY
Seismic StratigraphyWhy doing Seismic straigraphy?
• Geological age correlations
• Thickness estimates• Environment of deposition
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• Paleobathymetry
• Burial history
•Relief
• Topography on unconformities
• Lithology
• Porosity/permeability
• Fluid content
• Insight into source and seal
Seismic StratigraphyScale of Study
There are three scales for seismic straigraphy studies:
• Regional Scale Seismic Strat-Interpretation – Large-scalestratigraphic interpretation of data “seismic stratigraphy”.
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g p p g p y
• Prospect Scale Seismic Strat-interpretation. Localized
interpretation to define a prospect. May include use ofreflection configurations, wave shape, amplitude, etc.
• Reservoir scale Seismic Strat-interpretation. Quantitativelycharacterize reservoir (net sand, phi-H, etc.) to permit reservedetermination, reservoir simulation ,etc…
Seismic Stratigraphy
• Why doing seismic stratigraphy?
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• Scale of seismic stratigraphy study
• Assumptions
• Categories
Seismic Stratigraphy Assumptions for Reflection Character Analysis
• Reflections are boundaries of impedance contrast.
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• Reflections have areas in excess of the first Fresnel zone or .
• Reflections are from bedding surfaces.
• Reflections parallel time/age lines.
2-Seismic Stratigraphy
•Definitions
• Why doing seismic stratigraphy?
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• Why doing seismic stratigraphy?
• Scale of seismic stratigraphy study
• Assumptions
• Categories
Seismic StratigraphyCategories
Seismic stratigraphy is divided into two main categories:
• R fl ti h t l i
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• Reflection- character analysis
•Seismic facies analysis
2-Seismic StratigraphyCategories- Reflection Character Analysis
Reflection character analysis
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Analyse the lateral variation of an individual reflectionunit or units in order to localise where stratigraphic
changes are found and identify their nature.
Seismic StratigraphyCategories- Reflection Character Analysis
621
2322
24
56
234
21
23
227
8
222321
Reflector terminations defining the upper and lower boundaryof a sequences
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Onlap aboveTilting or original depositional
attitude
123456
1234567
8
9
21 2322 24 25 26
1 2 3
4
24
212223
56
1234
21 2322 24 25 26
12 5 61 2 3 4
7
212322 24 25 26
12
3
1
234
2122
23
123456
23
22
24
21
7
8
9
Concordant aboveErosional: angular, structural
Downlap aboveErosional: angular, structural
Onlap aboveErosional: angular, structural
Onlap aboveErosional: angular, nonstructural
Downlap aboveErosional: angular, nonstructural
Concordant aboveToplap below
Concordant aboveConcordant below
Downlap aboveConcordant below
2-Seismic StratigraphyCategories- Reflection Character Analysis
Reflector terminations defining the upper and lower boundaryof seismic sequences
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Seismic StratigraphyCategories- Reflection Character Analysis
Toplap (Upper Boundaries)
It is a termination of strata, or seismic marker, against an overlying surfacemainly resulting of non-deposition (sedimentary bypassing) with perhapsonly minor erosion. Each unit of strata laps out in a landward direction atthe top of the unit, and each successive termination lies progressively
d
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seaward.
Seismic StratigraphyCategories- Reflection Character Analysis
Toplap
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1- Coastal toplap
2- Marine toplap
3- Non-marine toplap
2-Seismic StratigraphyReflection Character Analysis
Toplap
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1- Coastal toplap
Seismic StratigraphyReflection Character Analysis
Toplap
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2- Marine toplap
Seismic StratigraphyReflection Character Analysis
Toplap
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3- Non-marine toplap
Seismic StratigraphyCategories- Reflection Character Analysis
Mark Toplap
(Upper Boundaries)
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2-Seismic StratigraphyCategories- Reflection Character Analysis
Erosional truncation (Upper Boundaries)
Where inclined strata terminate against an erosional surface.
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An unconformity is an erosional surface that separates younger strata from older rocks andrepresents a significant hiatus (at least a correlatable part of a geochronologic unit is notrepresented by strata). In very particular cases, an unconformity can corresponds to an non-depositional surface. Periods of erosion and non deposition occur at each global fall of sea levelproducing interregional unconformities. Although in some areas of continuous deposition, the
hiatus may be too small to be detected paleontologically or seismically, and the surface is definedas a conformity.
Seismic StratigraphyCategories- Reflection Character Analysis
Erosional truncation (Upper Boundaries)
.
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Seismic StratigraphyCategories- Reflection Character Analysis
Mark Erosional truncation
(Upper Boundaries)
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Seismic StratigraphyCategories- Reflection Character Analysis
Onlap (Lower Boundaries) If a period of deposition dominated by bedload transport ( sandsized materials) ceases and is followed by a period of depositionfrom suspended load, then filling the latter ususally produces anonlapping sequence.
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Seismic StratigraphyCategories- Reflection Character Analysis
Onlap 1-Proximal onlap
2-Distal onlap
3-Coastal onlap
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p
4-Marine onlap
5-Apparent onlap
6-Nonmarine onlap
7-True onlap
8-Tilted onlap (Apparent downlap)
Seismic StratigraphyCategories- Reflection Character Analysis
Onlap
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1- Proximal onlap : is onlap in the direction of the source ofclastic supply.
Seismic StratigraphyCategories- Reflection Character Analysis
Onlap
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2-Distal onlap onlap in the direction away from the source of
clastic supply.
Seismic StratigraphyCategories- Reflection Character Analysis
Onlap
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3-Coastal onlap is the progressive landward onlap of the coastal
deposits in a given stratigraphic unit.
2-Seismic StratigraphyCategories- Reflection Character Analysis
Onlap
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4- Marine onlap is the onlap of marine strata, primarily deep
marine (deposited seaward of the shelf break) in nature.
Seismic StratigraphyCategories- Reflection Character Analysis
Onlap
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5- Apparent onlap is the onlap observed in any randomly oriented
vertical section, which may or may not be oriented parallel todepositional dip.
Seismic StratigraphyCategories- Reflection Character Analysis
Onlap
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6- Non-marine onlap is the onlap observed in non-marine
environments, that is to say, landward of the depositionalcoastal break.
Seismic StratigraphyCategories- Reflection Character Analysis
Onlap
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7- True onlap : when two apparent onlaps are observed on two
sections intersecting at right angles, the true onlap is likely to beobserved on the section parallel to the depositional dip.
Seismic StratigraphyCategories- Reflection Character Analysis
Onlap
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8- Tilted onlap is an apparent geometrical relationship, that looks
like a downlap. Generally, it is induced by tilting, compensatorysubsidence and salt or shale flowage.
Seismic StratigraphyCategories- Reflection Character Analysis
Mark Onlap
(Lower Boundaries)
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Seismic StratigraphyCategories- Reflection Character Analysis
Mark Onlap
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Seismic StratigraphyCategories- Reflection Character Analysis
Onlap
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Faulted units beneath the NW continental margin of Australia, blanketed by a post-tectonic sedimentarycover of late Mesozoic and younger age. The faults are shown here as showing normal throws. However,there may be partial inversion of these structures to create the antiformal structure on the NW side of the
section. The post kinematic section lies on an erosional unconformity and onlaps significant relief acrossthe section. Author: Rob Butler
Seismic StratigraphyCategories- Reflection Character Analysis
Mark Onlap
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Profile across part of the Central Basin, Iran, NE of the city of Qom. Image from Morley et al.
(in press, 2009) Structural development of a major Late Cenozoic basin and transpressionalbelt in Central Iran: the Central Basin in the Qom-Saveh area. Author: Chris Morley
Onlap
Seismic StratigraphyCategories- Reflection Character Analysis
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Seismic StratigraphyCategories- Reflection Character Analysis
Mark
1-Onlap2- Erosional Truncation
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A dipline (see the associated regional project for location) with a well location marked. Note theangular truncation and erosion of the carbonates below the major unconformity associated withthe karstification of the carbonates. This erosion formaed a distinct penenplain, that is readilytraced across basement rocks (right) into the karsted carbonates at the well location.
Mark Onlap
Seismic StratigraphyCategories- Reflection Character Analysis
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An interpretation of thefault geometry and basinfill in part of the Inner
Seismic Stratigraphy
Categories- Reflection Character Analysis
Onlap
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pMoray Firth. Thisinterpretation was done
using 2D seismic dataalone (see relatedregional line) andwithout reference toexternal data or models.The arrows denote stratal
terminations (onlap).
Seismic StratigraphyCategories- Reflection Character Analysis
Mark 1-Onlap2- Erosional Truncation
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Seismic StratigraphyCategories- Reflection Character Analysis
Mark 1-Onlap2- Erosional Truncation
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Seismic StratigraphyCategories- Reflection Character Analysis
Downlap (Lower Boundaries)
Seismic reflection of inclined strata terminate downdipagainst an inclined or horizontal surface
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Surfaces are present at the base of prograding packages. They are commonly associated withmaximum flooding surfaces produced by a rise in relative sea level
Seismic StratigraphyCategories- Reflection Character Analysis
Downlap
1- Distal downlap
2- False downlap
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3- Shelf downlap
4- Basin downlap
5- Opposite (local) downlap
6- Apparent downlap
Seismic StratigraphyCategories- Reflection Character Analysis
Downlap
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1- Distal downlap is a downlap in the direction away from the source of clastic
supply. The majority of downlaps are distal downlaps.
Seismic StratigraphyCategories- Reflection Character Analysis
Downlap
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2- False downlap is a downdip tangential stratal termination. Strata flattenand continue as units, which, often, are so thin that they fall below theseismic resolution.
2-Seismic StratigraphyCategories- Reflection Character Analysis
Downlap
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3- Shelf downlap is a downlap recognized in a shelf. Often, it underlies the
slope of a depositional coastal break. The water depth is less than 200meters (prodelta).
Seismic StratigraphyCategories- Reflection Character Analysis
Downlap
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4- Slope downlap is a downlap associated with a continental slope.
The water depth is higher than 200 meters.
Seismic StratigraphyCategories- Reflection Character Analysis
Downlap
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5- Opposite downlaps are characteristics of overbank deposits,
whether associated with fluvial or turbiditic levees
Seismic StratigraphyCategories- Reflection Character Analysis
Downlap
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6- (Apparent downlaps) : original onlap terminations when deformed
by tectonics or halokinesis (salt tectonics) can become apparentdownlaps.
Seismic StratigraphyCategories- Reflection Character Analysis
Mark Downlap (Lower Boundaries)
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Seismic StratigraphyCategories
Seismic stratigraphy is divided into two main categories:
• Reflection- character analysis
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•
Seismic facies analysis
Seismic StratigraphyCategories- Seismic Facies Analysis
Why Seismic facies analysis
• Estimating deposition environment using thecharacter of the seismic reflections
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character of the seismic reflections.
• Understand depositional history.
•Locate and predict potential hydrocarbon reservoirand stratigraphic traps.
Seismic StratigraphyCategories-Seismic Facies Analysis
Seismic facies
It is the group of reflections bounded by top and base boundaries.
Seismic parameters used for facies detection are
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1)-Reflection configuration
2)-Reflection amplitude
3)-Frequency
4)-Continuity
5)-Interval velocity
Seismic StratigraphyCategories-Seismic Facies Analysis
•Bedding patterns
1- Reflection Configuration
Geologic Interpretation Facies Parameters
•Bedding continuity
•Depositional processes
2- Reflection Continuity
•Depositional processes
•
Fluid contacts
a) Internal config formsb) External config forms
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•Lithology •estimation
•Porosity estimation
•Fluid content•Pressure
5- Interval Velocity
•Bed thickness
•Fluid content
4- Reflection Frequency
•AI contrast
•Bed thickness (tuning)
•Fluid content
3- Reflection Amplitude
p p
Seismic Stratigraphy
Categories-Seismic Facies Analysis
1- Reflection Configuration
Internal & External Forms Configurations The overall geometry of a stratigraphic, or seismic unit, consists of the internal formand the external reflection configuration of the unit. Both must be described tounderstand the geometric interrelation and depositional setting of the units.
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•Internal Forms of Reflection Configuration (Filling pattern)
1-Onlap2-Prograding3-Mounded onlap4-Divergent5-Complex6-Chaotic
Internal Reflection Configuration (Filling Pattern)
Seismic StratigraphyCategories-Seismic Facies Analysis
Onlap Prograding Mounded onlap
1- Reflection Configuration
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Low-energy filling oferosional channel
Low-energy filling of erosionalchannel
Higher-energy fill
in at least two stages.
Very high-energy fill,possibly sand-prone.
Sediment transport over the edge of thechannel or along channel at a bend.
Compactable (shale-prone)low-energy sediments
Divergent Complex Chaotic
2-Seismic StratigraphyCategories-Seismic Facies Analysis
Internal Reflection Configuration (Filling Pattern)Onlap
Prograding
Mounded onlap
Divergent
Chaotic
1- Reflection Configuration
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Complex
Seismic StratigraphyCategories-Seismic Facies Analysis
1- Reflection Configuration
Mounded onlap
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Apparent Dip
relation to the
channel
Seismic Stratigraphy
Categories-Seismic Facies Analysis
1- Reflection Configuration
Internal & External Forms Configurations
The overall geometry of a stratigraphic, or seismic unit, consists of the internalform and the external reflection configuration of the unit. Both must be describedto understand the geometric interrelation and depositional setting of the units.
•Internal Forms of Reflection Configuration (Filling pattern)
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g ( g p )
1-Onlap
2-Prograding3-Mounded onlap4-Divergent5-Complex6-Chaotic
Seismic Stratigraphy
Categories-Seismic Facies Analysis
1- Reflection Configuration
Prograding Pattern types
Obli Oblique
Internal Reflection Configuration (Filling Pattern)
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Sigmoid
Tangential
Hummocky Clinoforms
Shingled Complex Sigmoid-Oblique
Oblique Oblique
Parallel
sheet drape wedge bank lens
Seismic StratigraphyCategories-Seismic Facies Analysis
1- Reflection Configuration
External Reflection Configuration
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fanmound
front slope fill channel fillTrough fill
Basin fill
Seismic Stratigraphy
Categories-Seismic Facies Analysis
Mound
External forms of reflection configuration
1- Reflection Configuration
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Seismic Stratigraphy
Categories-Seismic Facies Analysis
Trough Fill
External forms of reflection configuration
1- Reflection Configuration
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Seismic example illustratingthe complicated stratigraphyof a submarine slope valleyfill with adjacent leveedeposits. Image taken from
Mayall et al., 2006.
Seismic Stratigraphy
Categories-Seismic Facies Analysis
Front Slop Fill
External forms of reflection configuration
1- Reflection Configuration
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Seismic Stratigraphy
Categories-Seismic Facies Analysis
Basin Fill
External forms of reflection configuration
1- Reflection Configuration
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This 2D seismic line (BGS1993_02_C) is aligned NW-SE across the Hatton Basin. Buried volcanicescarpments are imaged on both margins of the basin. Each has a relief of c. 1 second TWT. The escarpments
are buried beneath the Tertiary sedimentary fill of the Hatton Basin, which thins towards the basinmargins, onlapping the flanks.
External forms of reflection configuration
Fan
Seismic StratigraphyCategories-Seismic Facies Analysis
1- Reflection Configuration
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External forms of reflection configuration
Channel fill
Seismic StratigraphyCategories-Seismic Facies Analysis
1- Reflection Configuration
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E W
2.2
2.1
---684m--
B
Seismic StratigraphyCategories-Seismic Facies Analysis
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A: Braided (low sinuosity, multi-channel stream)
B: Meandering (high sinuosity, single channel stream)C: Straight (low sinuosity, single channel stream)
A
C
External forms of reflection configuration
Channel fill
Seismic StratigraphyCategories-Seismic Facies Analysis
1- Reflection Configuration
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External forms of reflection configuration
1- Reflection Configuration
Incised Valley System
Seismic StratigraphyCategories-Seismic Facies Analysis
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SW
2.5
NENESW
SW
Seismic StratigraphySeismic Facies Analysis
1- Reflection Configuration
External forms of reflection configuration
Submarine Channel
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Pliocene submarine channel-Nile Delta
High
Low
2.75 02.5 km
Deposition occurs on inner
bends (point bars) and
erosion on outer bends.Cross-over reaches between
bends are largely area of
sediment transfer
Seismic StratigraphyCategories-Seismic Facies Analysis
External forms of reflection configuration
Incised Valley System
1- Reflection Configuration
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Incised Canyons sourcing sediment down slope Off shore Mediterranean
5 km
Mark Incised Valley System
Seismic StratigraphyCategories-Seismic Facies Analysis
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External forms of reflection configuration
Lens
Seismic StratigraphyCategories-Seismic Facies Analysis
1- Reflection Configuration
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Bank
External forms of reflection configuration
Seismic StratigraphyCategories-Seismic Facies Analysis
1- Reflection Configuration
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External forms of reflection configuration
Drape
Seismic StratigraphyCategories-Seismic Facies Analysis
1- Reflection Configuration
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2- Reflection continuity:
• Bedding continuity
• Depositional processesHigh Continuity(continuous strata deposited inwidespread and uniformenvironment, (marineconditions)
Seismic Stratigraphy
Categories-Seismic Facies Analysis
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Low Continuity(sediments deposited withvariable energy (by fluvial-Alluvial currents)
Difference incontinuity du todifferent shootingparameters
Seismic Stratigraphy
Categories-Seismic Facies Analysis
3- Amplitude
Low amplitudeHigh amplitude
Amplitude is the height ofreflection peak and it dependent
on the reflection coefficient.
•Vertical change in amplitude canbe used to locate unconformities.
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•Lateral change can be used to helpdistinguish seismic facies.
•Lateral changes in amplitude canhelp delineate the edges of brightspots
Seismic Stratigraphy
Categories-Seismic Facies Analysis
4- Frequency (Spacing)
It describes the number of reflections
per unit time .
• It is a function of both frequency ofseismic signal and interference effects
High frequency-small spacing
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seismic signal and interference effects.
•Vertical change in spacing can be usedto locate boundaries between
depositional sequences.
•Lateral change can be used to inferfacie
Low frequency-long spacing
Seismic StratigraphyCategories-Seismic Facies Analysis
5- Interval velocity:
Estimation of lithologyEstimation of porosity
Fluid content
Push down
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Velocity Anomaly - pull down
V1 < V2Push down (velocity sag) due
to gas accumulation Velocity: V=( /c)4
V1
V2 V2
V1 V2
V2
Seismic Stratigraphy
5- Interval velocity:
Estimation of lithology
Estimation of porosity
Fluid content
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Seismic Stratigraphy
5- Interval velocity:
Estimation of lithology
Estimation of porosity
Fluid content
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Seismic Stratigraphy
5- Interval velocity:
Estimation of lithology
Estimation of porosity
Fluid content
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Plio-Pleistoceneturbidities
Sea
Floor
Sea floor
Seismic StratigraphyCategories-Seismic Facies Analysis
5- Interval velocity: Push down Gas Chimney
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~ 100 ms
Top Reservoir(= Top A)
Gas chimney emanating from sinkhole;am litude reduction and structural as sa
Seismic StratigraphyCategories-Seismic Facies Analysis
5-Interval velocity:
Estimation of lithology
Estimation of porosity
Fluid content
Pull up & Pull down
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Velocity Anomaly - pull down
V1 < V2
Velocity: V=( /c)4
V1 V2
V2On this seismic line from offshore Angola, the pull-down ofthe yellow marker (bottom of the evaporitic interval) isinduced by the lateral change of the interval-velocity createdby the normal fault which limits a Upper Tertiary depocenter.Indeed, such a fault put limestones (upthrown block) and
shales (downthrown block in juxtaposition.
Seismic StratigraphyCategories-Seismic Facies Analysis
V1 V2 V2
5- Interval velocity:
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On this reef geological model, above a planar limestone sole (light blue), a reef with a compressional wavevelocity of 5490 m/s, is laterally bounded by shaly sediments (yellow) with a much lower velocity (3660 m/s),which are overlain by even slower sediments (brown interval, 3050 m/s). The seismic answer of such a model is
roughly depicted on the right. The horizon associated with the bottom of the reef shows a significant pull-up.
Velocity Anomaly - pull up
V1 < V2
Velocity: V=(
/c)4
Seismic StratigraphyCategories-Seismic Facies Analysis
5- Interval velocity:
V1 V2 V2
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Palaeozoic carbonate reef build-ups (Barents Sea)
Velocity Anomaly - pull up
Seismic StratigraphyCategories-Seismic Facies Analysis
5- Interval velocity:
PSDM Migration No pull up Time Migration- pull up anomaly from reef
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Seismic StratigraphyCategories-Seismic Facies Analysis
wedge
sheet
parallel, even,high amplitude
prograding
ll l di ti
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sheet
frontslope
fill
chaotic
moundprograding
subparallel
parallel, discontinuous,low amplitude
7- 4D
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What is 4D Seismic?
• Is the analysis of differences found in seismic surveys repeated inan area where substantial changes in the subsurface have
occurred, due to production processes– Qualitative
– Quantitative
P id i f ti ith l t l ti it th t id
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• Provides information with lateral continuity that provides a
VISION of actual changes in the reservoir– Fluid substitution
– Temperature
– …
4D Seismic - the Concept
• Also known as Seismic Reservoir Monitoring or Time-LapseSeismic
• Consists of 3D seismic surveys, repeated after intervals ofsubstantial production
• Successive surveys analysed for differences
Ob fl id h i th i
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• Observes fluid changes in the reservoir
• Available between & beyond the wells
Classification of Gullfaks data
1995 Difference1985
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SHCindicator0 1 No change Large change
34 well locations selected; additional 600 million bbl producible reservesfound as result of 4D
Continual Improvement
Foinaven Data, Norwegian Sea
1993
E W
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93 reprocessed 95
Flat Spot
Pioneer Examples: Duri Field
•Seismic image of DURI field, where
effects of steam injection are easily
visualized in the seismic data
•D. Lumley, 1995
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4D Interpretation Workflows
• Fluid substitution modelling
• Seismic repeatability assessment
• Seismic interpretation
• Seismic attribute extraction
• Classification (Inversion)
• Reservoir optimisation
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• Reservoir optimisation
4D WorkflowFluid
substitution,
AVO
modelling Interpretation Inversion-
Classification
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Seismic
repeatability
assessment,
wavelet, etc..
Seismic attribute
extraction
Reservoir
optimisation
Fluid Substitution
Synthetic Response to Change in Rock Physics
• Change of physicalparameters
• T dependence
• Fluid factor is veryimportant
• Change of physicalparameters
• T dependence
• Fluid factor is
very important
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TEMPERATURA 25A 7A 1A 3A 4A 8A 10A
24,00 2,92 2,65 2,67 3,01 2,81 2,84 2,81
40,00 2,74 2,54 2,56 2,87 2,68 2,64 2,68
60,00 2,52 2,38 2,40 2,70 2,44 2,46 2,53
80,00 2,36 2,22 2,20 2,60 2,31 2,27 2,42
100,00 2,27 2,08 2,11 2,50 2,17 2,15 2,32
125,00 2,17 1,99 2,02 2,41 2,06 2,05 2,19
150,00 2,08 1,91 1,95 2,30 1,98 1,97 2,11
1,70
1,90
2,10
2,30
2,50
2,70
2,90
3,10
24,00 40,00 60,00 80,00 100,00 125,00 150,00
Serie1
Serie2
Serie3
Serie4
Serie5
Serie6
Serie7
Serie8
Serie9
Serie10
Serie11
Serie12
Serie1328 % 28 %
LS - 2203
T
V
importantvery important
4D (Time-Lapse) SeismicGullfaks Field, North Sea
Mapping fluid movements and identifying unswept hydrocarbons
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SHC indicator0 1 No change Large change
1989 1996
Time Lapse SeismicSleipner CO2 Storage
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1994 1999 2001Monitoring of C02 injection in aquifer
Data courtesy of Statoil
Time Lapse Seismic
Sleipner CO2 Storage
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Seismic 1999 Seismic 2002
Amplitude difference and vertical time shift due to cumulated gas effectconduct to erroneous 4D effect if not compensated
Data courtesy of Statoil
4D Summary
• 4D seismic provide important information for decision making analysis
in reservoir management
• Tailor made interpretation tools and workflows for 4D analysis
• Demonstrated the use of qualitative or semi-quantitative 4D analysis
for updating reservoir models
• Seismic to Simulation and Simulation to Seismic (S2S) are established
workflows
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workflows
• Beyond qualitative interpretation, the link between reservoirengineering and geophysics via rock physics enables quantitative 4D
analysis for reservoir management
What is a Neural Network?
Neural Networks:
• recognize ill-defined patterns without an explicit set of rules
• may adaptively infer heuristic knowledge from sample data
• unlike statistical estimators, they estimate a function without amathematical model of how outputs depend upon inputs
• they are model free estimators, they “learn from experience” with
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y y pnumerical and , sometimes, linguistic sample data
• like brains, they recognize patterns we can not define, or what iscalled recognition without definition
OGCI - SER - Neural
Networks and Seismic Facies -
429
Stratigraphic Interpretation
Seismic Facies: The description and geologic interpretation of seismicreflection patterns including configurations, (continuous, sigmoidal, etc.),frequency, amplitude, and continuity.
Neural Network Technology (NNT): The ability to analyze and classify
Seismic Facies Analysis using NNT: What Is It ?
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trace shapes using a discriminating process.
Seismic Facies Map: This is a similarity map of actual traces to a setof model traces that represents the diversity of various trace shapespresent in an interval.
Example for using NNT- Texas Ranch 3D
• 3D Survey - DeWitt Co., Texas
360 inlines - 382 crosslines
82.5’x82.5’ bin spacing (34 sq.miles)4 seconds of data @ 4 msec
W ll D t
Well A(~0.1
MMCFD)
Well B(~1
MMCFD)
N
EW
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• Well Data
Two wells drilled in main channelWell A - 15ft wet sand (“fizzy” water) Well B - 30ft gas sand
1mile
1
mile
E W
S
SW NEWell B
The Play: Frio Channel Sandstones
Well A Well BRandom Line
“Gas production comes from Oligocene Frio sandstonesdescribed as fluvial channel fills, point bars, and splay depositsdeposited in a plain mudstone”.
R f
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Reference
Horizon
FrioChannel
Structural Interpretation
• Horizon Attributes
Time Horizon Map combined
with seismic amplitude atreference horizon.
Note Channel systems.
Stratigraphic play with
B
A
Mixed map: Time (in color) and amplitude (in B&W)
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Stratigraphic play with
several braided fluvialsystems with bright spots.
… structure-independent.
Structural Interpretation
• Time Slice
Taken at 824 msec.
Main Channel clearlyidentified by bright spots.
Is there a break in the
B
A
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channel?
Why are the wells different?
Stratigraphic Interpretation
• Horizon Slice
Parallel to ReferenceHorizon - 92 msec below.
Continuous channel nowclearly seen.
B
A
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Still cannot adequatelyexplain differences atwells.
Stratigraphic Interpretation
Seismic Facies: The description and geologic interpretation of seismicreflection patterns including configurations, (continuous, sigmoidal, etc.),frequency, amplitude, and continuity.
Neural Network Technology (NNT): The ability to analyze and classifyt h i di i i ti
Seismic Facies Analysis using NNT: What Is It ?
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trace shapes using a discriminating process.
Seismic Facies Map: This is a similarity map of actual traces to a setof model traces that represents the diversity of various trace shapespresent in an interval.
Stratigraphic Interpretation Part I
• UnsupervisedRegional Seismic
Facies Analysis
Horizon slices indicate verticalchannel extent of approx. 40 msec.
B
A
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Seismic Facies map of entire areaover the 40-msec interval and 15model traces.
Channel system characterized bymodel traces 1,2, and 3.
Stratigraphic Interpretation Part I
• Conventional AmplitudeVs. Seismic Facies Approach
The seismic facies map is very…colorful, but we still cannotdifferentiate between the twowells
B
A
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wells.
Why use seismic facies technologyif it provides the same results as anamplitude-based approach ?
B
A
Stratigraphic Interpretation Part I• UnsupervisedChannel SeismicFacies Analysis
Seismic facies map over thechannel system shows a traceshape difference between the Aand B wells
B
A
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What is the meaning of thistrace shape variation ?Lithology ?Porosity ?Fluid content ?
Petro-Acoustic Modeling• Modeling at Well A
1 2 3 4 65 7 8 9
Input is well logs, seismicfacies model trace, andseismic traces.
Synthetic Seismogramgenerated and calibrated to
Well A Well B
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generated and calibrated to
seismic traces.
Model now modified withproperties observed at WellB (30-ft sand). Trace shapechange replicates variation
between A and B.Red=Sonic
Blue=Density
Stratigraphic Interpretation Part II
• 3D Model-BasedPropagation of theMain Channel
Time map of channelhorizon generated usingseismic character at wellsA and B
B
A
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A and B.
Note: Well A structurallyhigher than well B in thetime domain.
B
Stratigraphic Interpretation Part II
• Supervised SeismicFacies Analysis
“Focused” interpretation, based onpetro-Acoustic modeling results andareal isolation of channel system. B
A
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Model indicates that interval affectedby sand property changes is wider -increase to 72 msec (12 model classes).
Note difference in trace shape at wells.
B A
Stratigraphic Interpretation Part II
BARandom line throughwells.
BEFORE showsunsupervised seismicfacies (similar atwells).
BEFORE
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AFTER showssupervised seismicfacies (different atwells).
AFTER
Stratigraphic Interpretation Part II
Final Seismic Facies Map of
channel system (in color), mixed
with average amplitude (in B&W)over same interval.
Note channel to south of Well B.B
A
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Neural Networks Consist of:
• numerous, simple processing units or “neurons” that we canglobally program for computation.
• They can be programmed or trained to store, recognize, andassociatively retrieve patterns or database entries to solvecombinatorial optimization problems, to filter noise frommeasurement data, to control ill-defined problems - toestimate sampled functions when we do not know the form of
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estimate sampled functions when we do not know the form of
the functions• artificial neural systems may contain millions of nonlinear
neurons and interconnecting synapses and future systemsmay contain billions of real or virtual model neurons
445
Natural Fracture Classification( A Genetic Classification )
• Tectonic Fractures
– Fold-related, Fault-related• Regional Fractures
– Joints, Cleat
• Contractional Fractures
Chi k i Di i l d C l J i
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– Chickenwire, Diagenesis-related, Columnar Joints
• Surface-related & Induced
– Unloading, Spall, Weathering
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Fractures Surrounding a Normal
Fault in Miocene Ss
Western Sinai,
EgyptHangingwall
East West
S 1
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10 ft
Footwall
S 3S 3
Fractures Around a Normal Fault
Clastics, Brunei
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1 ft
Variations in Fracture Intensity Associated with
Faults are Due To:1. Pre-Slip Effects
• Fracture zone preparing the rock mass for fault slip (halo zone).
• Precedes propagating fault.
• Interactions between propagating fault tips and halos.2. Effects Occurring During Slip
• More fracturing as “hanging wall” moves over an irregular faultsurface.
• Intense deformation occurs at the slip surface leading to a
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p g
“damage zone”. 3. Post-Slip Effects
• The presence of faults can warp today’s reservoir stress stategiving local changes in fracture permeability.
• More fractures could be created if the faults are reactivated &/or
inversion takes place (local fracture overprinting).
R.A. Nelson 9/02
Process zone fracturing surrounding a Normal Fault
k
max ?
k min
Volume of rock
fractured prior to
through-going fault
slip
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Effective Process Zone (a few hundred feet)
Damage Zone (c. a few
feet)Not to scale
Effective process zone is
the zone that issignificantly greater than
matrix flow.
Damage zone is usuallylow in permeability.
Background
fractures related
fractures due to
normal stress state.
Pre-Slip Fracturing Forming the Process Zone
Fracture Swarm
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Background Fracturing
Onset of Fault Slip: Propagating Slip Through
Process Zone
Extending
Process Zone
Process
Zone
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Propagating Slip
Surface
Fault Propagation Interaction in 3-D Creating
New Fractures
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Interacting Faults
Slip-Related Effects:
Fracturing Related to Fault Slip
• Additional fractures are generated as the hanging wall displacesover topography of the fault surface.
• Once generated at the asperity these fracture zones are translateddown the slip direction along the fault.
• If fault slip is small, little slip-related fracturing will take place.
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• Curvature maps of the fault surface can be used as a guide forthis prediction.
• Accurate fault plane mapping is critical in predicting these zonesof kinematic fracturing.
R.A. Nelson 9/02
Slip-Related Fracturing in Map View
Outside bend Inside bend
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High extensional strain High compressional strain
Displacementtransfer
Left-Lateral
Left-Stepping
Local Stress Variations at Fault Steps & Bends
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Right-Stepping
Schematic Map View of an Inversion Fault
with Changes in Fault Strike
Zone of maximum localcompressional strain
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Inversion-relatedcompression direction
Zone of maximumlocal extensionalstrain
Schematic Map View of an Inversion Fault with
Changes in Fault Strike
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Major InversionFault
Major InversionFault
Schematic View of Fracture Systems Associated with Secondary
Faults Along Inversion Faults with and without Strike-slip
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SecondaryAntithetic Faults Secondary Faults in a
strike-slip scenario
No Strike-slip With Strike-slip
Extension ZoneFracturing
Normal Fault With DipChanges in Cross Section
Kinematic Fracture Zones Associated with
Fault Topography in Cross Section View
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Compression ZoneFracturing
Schematic Cross Section of an Inversion Fault
with Changes on Fault Dip
Zone of localextensional strain
Zone of local
compressional strain
Post-rift
Only reversefault fracturesets
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Basement
Syn-rift
Post rift
Overprinted normal& reverse faultfracture sets?
Local Fracturing Due to Slip on an Irregular faultSurface
Compression ZoneFracturing
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Extension ZoneFracturing
Slip-Related Effects:
Deformation at the Slip Surface
•Once through-going fault slip occurs, the zone immediatelysurrounding the slip surface can experience intensedeformation. (“Damage Zone”)
•This deformation is quite variable and can range from purelyductile to purely brittle.
•There is a relationship between the properties of this zoneand amount of slip.
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•The width of these zones can be variable between faults andalong faults but range generally between 1 to 10 m.
•The width and properties of these zones are difficult topredict or image in the subsurface. Observational data basedon cores leads to the best predictions.
R.A. Nelson 9/02
Fracture Process Zone Surrounding a Planar
Normal Fault
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Normal Fault Reactivated as a Reverse Fault
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Overprinting
Mapping Fault Zone Properties
Geometry, Width and Intensity
1. Gather exploration & show history
2. Compile mechanical, petrophysical & production characteristics ofsection
3. Acquire and map surface & subsurface fracture distributions4. Determine fracture origin and make mechanical predictions of
orientation & intensity
5. Determine in situ reservoir stress directions and magnitudes
6. Constrain subsurface fracture intensity, width, & zone widths and
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lengths from image logs, core, and geophysical Attributes7. Predict fracture distribution “sweet spots” from the above
8. Model reservoir volumes of the fracture system
9. High-grade and prioritize potential locations via checklist
10. Select well paths to optimize fracture intercept rate and chooseoptimum completion technique
Fold-Related Fractures
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Phosphoria Ls, Black Canyon Anti., WY
Fold-Related Fractures