qab2054 intro rx physics [compatibility mode]

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Seismic InterpretationSeismic InterpretationQAB 2054QAB 2054

SeismicSeismic Spectral AttributesSpectral Attributes

GeoscienceGeoscience and Petroleumand PetroleumEngineering DepartmentEngineering Department

6th6th October 2010October 2010

o Seismic attributes in perspective

Outline of lecture:-

o Seismic stratigraphic analysis

o Seismic wave propagation

o Seismic spectral analysis

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attributes

o Application of specdecom attributes


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Outcomesof

the

lecture:

Knowledgeof seismicwavespectrums

Awareofspectralanalysisprocedures

Describeapplicationofspecdecom in

seismic interpretationjob

Inter retation skill in seismic

stratigraphic domains

SeismicAttributesarespecificmeasuresofgeometric,kinematic,dynamic,and


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Measuresof:

Reflectoramplitudeandtime,energybetweenformationtopandbottom(reflectors),reflectordipandazimuth,illumination,coherence,amplitudeversusoffsetandspectraldecomposition

egenera a r u escanre a e rec y os ra grap cdeposition(depositionalfacies),tectonicdeformation,and

reservoirproperties

ATTRIBUTE CLASSIFICATION

GEOMETRIC SPECTRAL AVO

. DIP / AZIMUTH . INSTANTANEOUS(Amp, freq, phase)

Acoustic Impedance

Elastic Im edance

.

. COHERENCY

WAVEFORM CLASS

. SPEC. DECOMP

Intercept

Gradient


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- Surve and Positionin- Seismic Survey Design

GEOPHYSICAL EXPERTISE

GEOPHYSICAL CLASSIFICATIONGEOPHYSICAL CLASSIFICATION

GEOPHYSICS

SEISMOLOGY - Seismic Data Acquisition- Seismic Data Processing

- OBC 4 C / Shear Seismic

SEISMICINTERPRETATION

3D Visualisation

Volume Interpretation

Exploration Success Through

Innovative Solutions

QUATITATIVEGEOPHYSICS

- AVO & Rock Physics- Seismic Inversion

- Structural Modeling & Imaging- Seismic Attribute Analysis- Time Lapse Seismic

GEOMORPHOLOGY

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Erosional Truncation Top Lap Concordance

Seismic Attributes should able toHel the identification of these

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On lap Down lap

Geological fealures.

Dip / Azimuth Coherency

Instantaneous Attribute


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SEISMIC STRATIGRAPHY

Classify the Seismic Section into Geological Units based on

Frequency

Continuity

Frequency ContinuityAmplitude

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L

M

H

L

M

H

L

M

H

Seismic Waves Surface Waves

Body Waves

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1. P-wavesParticle motion parallel to wave propagation

wavedirection

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2. S-wavesParticle motion perpendicular to wave propagation

Seismic Wave PropagationSeismic Wave PropagationAn impulsive force like a blast from dynamite source or Air gun creates a seismicAn impulsive force like a blast from dynamite source or Air gun creates a seismicwave that propagates in the earth . Waves can travel inside the earths body or onwave that propagates in the earth . Waves can travel inside the earths body or onthe surface of the earththe surface of the earth

v yv y ::There are two types of waves : Body waves like P Longitudinal waves and S: ShearThere are two types of waves : Body waves like P Longitudinal waves and S: Shearwaves .Surface waves are called Rayleigh and Love waves. In contrast to bodywaves .Surface waves are called Rayleigh and Love waves. In contrast to bodywaves ( in seismic band ) surface waves arewaves ( in seismic band ) surface waves are attenuativeattenuative and dispersive.and dispersive.

BODY WAVE : P & SBODY WAVE : P & S

Particle motion in P waves is in the same direction as the wave, . P waves areParticle motion in P waves is in the same direction as the wave, . P waves arecaused rimaril b chan e in volume . P wave velocit de end hence on Bulkcaused rimaril b chan e in volume . P wave velocit de end hence on Bulk

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modulus Kmodulus K Longitudinal P wave (Compressional & Refraction)


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TRANSVERSE OR SHEAR WAVE

Shear Wave on the other hand are created due to

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motion is perpendicular to the direction of propagation

of wave.

SEISMIC REFLECTION PROCESS IN EXPLORATION

Fig 1(b)

The physical process of reflection is illustrated above for one reflector in (a) and severalsuccessive reflector in depth in ( b), There are commonly several layers beneath the earth'ssurface that contribute reflections to a single seismogram. The unique advantage of seismicreflection data is that it permits mapping of many horizon or layers with each shot.

Fig 1(a)

14Multi-channel recordings for seismic reflection

Figure 2 indicates the arrivals that recorded on a multi-channel seismograph. Note that the subsurfacecoverage is exactly one-half of the surface distanceacross the geophone spread. The subsurface samplinginterval is one-half of the distance between geophones

on the surface


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Vertical (Temporal) Resolution Limits

Full Wavelength

Resolved Layer

Half Wavelength

Resolved Layer

Quarter Wavelength

Unresolved Layer

(Detected)Single Reflection

No Layer

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Physical Factors Affecting Seismic Wave Propagation

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Convolutional Model

+ =Time

*

Source Input Earth Noise Seismic traces

SEI SMI C TRACE

0- +

High Frequency10 60 Hz (Cycles/sec)

Polarity (Hard)(Soft)

Amplitude (-)

(Reservoir)

0 Phase

90 Phase

ase

Wavelength= v /= 3000/30

Resolution = 25 m

= 100 m

Low Frequency6 35 Hz


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Wave l e t shape

Poss ib le Se ism ic Sign at ur es

cous c mpe ance

Reflectivity

Time Dip

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Curvature

time

0

functionoffrequencyforthecomponentsofawavetrainorwavelet

Fourieranalysisinvolvefindingfrequency

Fouriertransformisconversionoftimefunctionintofrequencydomainrepresentationandviceversa


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Decompositionofmeasuredsignalsintospectralour er componen s oa enua e ow requency

groundrole(culturalnoise),andhighfrequencyrandomnoise.

Spectraldecompositionisalsoknownasshortwindowdiscretetransforms

ses x engt ana ys sw n ow ora requenc es,allowingustocomparewhichfrequencycomponentismoredominantinageologicformation

Interpretersareconcernwithwhatfrequencytuningoccurs

DiscreteFouriertransformdecomposethedataintos nuso a componen ssepara e y1 o2 z or nerfeaturesofinterest,otherwiseweneedonly todecomposedataat10Hzintervalsforbandlimitedseismicdataof100mswindow

Spectralcomponentimageswithhigherlateral

amplitudedataprovided.

Appropriateforformationbasedattributessuchastuningthicknessandmappingstratigraphic variability.

(Marfut,2006,SEGDISNo.9)


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20 Hz

50HZ

20ms

Concept of Spectral analysis

20 ms

FREQ.

50 MS

DBFREQ.

TUNNINGShale

Amp

THIN

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THICKNESS (MS)

THIN BED TUNNING & RESPONSE

50 ms

THICK

WELL A WELL B

SPECTRAL ANALYSIS SPECDECOMP

55HzLowFrequency

HighFrequency

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FREQUENCY

35Hz

Courtesy Petrofac

Two wells show different facies. Well A is high frequency. B low frequency.Well A peaks at 55hz and B at 35hz Specdecomp Spectral analysis ( extreme right )

reveals the channel. Thinner beds respond to high frequency.


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NUMERICAL GEOLOGICAL MODELLING

VALLEY

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TRANSFER

FUNCTION

CHANNEL

CHANNEL MODELLING

Wavelet Classif ication (Seismic-Facies)

Classify seismic trace shapes intoseismic facies within an interval(constant or variable thickness)

B100CL 5to25ms 12 class B80-B100cl, 12 classes

us ng eura e wor ec no ogy

26Channel signatur e


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Specif ic Examples of Seismic At t ribut es Maps

Channel paths

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Rms amplit ude Wavelet class specdecomp

ThankyouFORYOURATTENTION

qab2054 intro rx physics [compatibility mode]

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