Basic Seismic Interpretation

8/20/2019 Basic Seismic Interpretation

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Introduction – Geophysical Methods


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Most geophysical surveying methods can be used either on land or offshore. Each of these methods measures a

parameter that relates to a physical property of the subsurface. List of different methods, the parameters they measure,

and the related rock properties are indicated in the table 1

able 1 Geophysical !urveying Methods

ME"#$ ME%!&'E$ (%'%MEE'(")!I*%L ('#(E') ME%!&'E$ #'

$E'I+E$

!EI!MI* '%+EL IME %$ %M(LI&$E #'

'E-LE*E$'E-'%*E$ !EI!MI* /%+E!

EL%!I* M#$&LI, ('#(%G%I# +EL#*I),

$E!I)0

G'%+I) !(%I%L +%'I%I#! I "E !'EG" #- "E

E%'"! G'%+I%I#%L -IEL$

$E!I)

M%GEI* !(%I%L +%'I%I#! I "E !'EG" #- "E

GE#M%GEI* -IEL$

M%GEI* !&!*E(I2ILI)

ELE*'I*%L

'E!I!I+I)

E%'" 'E!I!%*E ELE*'I*%L *#$&*I+I)

!EL-3(#EI%L ELE*'I*%L (#EI%L ELE*'I*%L *#$&*I+I)

ELE*'#3M%GEI* 'E!(#!E # ELE*'#M%GEI* '%$I%I# ELE*'I*%L *#$&*I+I) %$

I$&*%*E


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2oat

*able 4ith hydrophones

!ea !urface

!ource

5%irguns6

'eflected

4aves



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Measure:Measure:

. ravel time. ravel time• %mplitude%mplitude

Infer:Infer:

. +elocity. +elocity

!ource 'eceiver

Introduction – !eismic /ave

'eflector


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!eismic raceThe basic unit of seismic data

%mplitude

7 83

r a v e l i m e

Introduction3!eismic race


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• A seismic survey generates a large number of shot records to cover the area under study.

Many stes of rocessing are alied to the data to enhance the signal! to minimi"e noise!

and to increase resolution. All the traces corresonding to a surface midoint are combined

into a single trace! called a common-mid-point stack.

• !eismic section

#hen rocessing is comlete! all the common$deth$oint stac%s are dislayed side by side

to ma%e a seismic section! &hich is the final outut of a 2' seismic survey.

A Seismic Section

!eismic race, 'ecords and !ection


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Introduction


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Introduction


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Introduction

Loaksi bidang pantul 5'eflektor6 9

:arak ; + < = 4aktu

pantul

+ 9 kecepatan rambat gelombang suara di udara


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Introduction


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Introduction


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• Introduction

• 2asic !eismic (rinciples!eismic 4ave propagation

!nells la4'eflection, refraction and critical angle%coustic impedance'eflection coeficient

!eismic polarity and phase/avelet and convolution!ynthetic seismogram

• !eismic $ata %c>uisition

2asic !eismic (rinciples


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2asic !eismic (rinciples

Gelombang seismic merupakan gelombang akustik,

serupa dengan cahaya

(ada dasarnya kita gunakan gelombang seismic untuk

pencitraan lapisan3lapisan ba4ah permukaan bumi,

melalui pendeteksian response dari bumi apabila diberi

gangguan energy

$asar hukum dari seismic refleksi dikembangkan oleh

/illebrord !nell yang dikenal dengan ? !nell La4@

Incident (34ave 'eflected (3

4ave

'efracted (34ave

+1

+A

+1 B +A

θ

θ

θ

2


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!nells La4 of 'eflection %nd Interpretation


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+elocity, %coustic Impedance dan 'eflection *oefisien

+elocity dan $ensity adalah acoustic parameter yang

menentukan respons seismic refleksi

%coustic impedance adalah produk dari density dan

velocity

Coefisien refleksi adalah prosentase dari energy yang

direfleksikan oleh bidak batas antar lapisan

Imp ; 'ho < +elocity

'c ; 5ImpA – Imp165ImpA 8 Imp16


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!eismic $ata Duality

! ratio 0

*ontinuity0


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%natomy dari !eismic !ection

Menunukkan lapisan3lapisan batuan 5Lithology6 yang

berbeda

+ertical scale bukan depth 5kedalaman6, melainkan

/aktu tempuh 5travel ime6

Informasi dapat menunukan structur ba4ah permukaan

5subsurface6, stratigraphy atau kedua3duanya. "ati3hati

dengan artifact.

"oriFontal scale adalah *$( atau !( dan vertical scale

adalah / 54o 4ay ime6


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2asic !eismic (rinciples3%natomy Gelombang


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!hear 4ave 9 arah gerakan partikelnya tegak lurus terhadap arah rambat


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%mplitude 9

-re>uency 9 :umlah gelombang dalam satu detik

(erioda 9 4aktu yang ditempuh untuk membentuk satu gelombang

Magnitude gelombang

(anang gelombang 5lambda6 9 :arak satu gelombang


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-re>uency ;

Lambda ;

(anang gelombang 5lambda6 ; +elocity < (erioda

1 (erioda

+elocity < -re>uency


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!eismic images geology


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'eflection dan ransmission *oefficient


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2asic !eismic Interpretation3 E


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'esolution

Cetebalan terkecil yang dapat diresolve

5dilihat top dan bottomnya6 oleh seismic 9

; H Lambda

; H 5+elocity-dom6

-dominan ; = -ma


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'esolution


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'esolution


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'esolution


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/ell – !eismic *alibration

• *heckshot

• !onic 5$6

• $ensity 5'"#26

• Gama 'ay 5G'6

• *aliper

• 'esistivity 5'6

• GR, RT and Caliper are useful to assist in the editing of the sonic and

density logs (to correct any noise spikes, cycle skips, bad splices etc.).

$ata (reparation


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/ell – !eismic %*D&I!II#

,urvey boat

-ro &ell traectory

+!( Loging &nit

/avigation monitoring

&hen erformed 0,- for

deviated &ell


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/ell – !eismic %*D&I!II#Barge Set-uP for Offset VSP

Two air gunsat 150 cu. in.

each.

3.5m

Crane

Water depth 5 m

minimum (ow tide!.

" m minimum distance

#etween #arge hu and

air guns. T$% sa&et'

reguation

1m

)'drophone 1m

a#o*e airgun

Bac+up

)'drophone 1m

a#o*e h'd1


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/ell – !eismic %c>uisition


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!ynthetic !eismogram Generation /orkflo4

'a4 !#I* *heck !hots '"#2

*alibrated !#I*

$'I-

%coustic Impedance

'eflection *oefficients /avelet

!ynthetic !eismogram

*omposite or -inal *alibration (late

/ell ie

3 'icker

3 E


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!EI!MI* %*D&I!II#

arth #avelet ,eismic Amlitudes

B,-

"ypothesis"ypothesis

he seismic trace ishe seismic trace is

the result of athe result of a

convolutionconvolution bet4eenbet4een

a 4avelet anda 4avelet and

earth reflectivitiesearth reflectivities

%mplitudes


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%mplitude generation

;

!eismic trace%coustic

impedance Log

'i;5%i813%i65%i818%i6

Impedance

'eflectivity

J derivation K

%i81 ; %i518'i6518'i6

J integration K

4avelet

convolution

8 noise

Acoustic imedance - velocity density

ey etrohysical arameter of the roc%


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/ell !eismic calibration (erformed in *harisma


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ama ray

!

y n t h e t i c ! e i s m o g r a m

!urface !eismic

/ell !eismic calibration (erformed in Geolog


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/ell !eismic *alibration (late

Time shift bet&een

seismic and synthetic

seismogram.

N1O ms is alied to

surface seismic


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•-aults (icking

•"oriFons (icking

Inline

*rossline

!eismic 'eflection Interpretation


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Increment




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Interpolation using ASAP in Geoframe



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Fault & Horizons Picing



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Fault & Horizons Picing


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Mapping and *ontouring


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Mapping and *ontouring


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I t d ti


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Introduction

hh


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( l it


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(olarity

I t d ti


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Introduction

2 i ! i i I t t ti ' f ti


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2asic !eismic Interpretation 3 'efraction

2 i ! i i I t t ti ' f ti


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2asic !eismic Interpretation3'efraction


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2asic !eismic Interpretation


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2asic !eismic Interpretation

Interval +elocity for .!I!I31, !I!I3P and &2I3A


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0int 26++

m?s

0int 325+

m?s

0int 36++

m?s

0int 2(++

m?s

0int 34++

m?s

0int 3)++

m?s

0int 265+

m?s

0int 34++m?s

0int 3)++

m?s

/.,


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'esolution vs $epth

1+++

15++

2+++

25++

3+++

35++

1+ 2+ 3+ 4+ 5+

thickness

G 5 m s s 6

NB-2

SISI-7

NSISI-1

P oly. (SISI-7)

P oly. (NB-2)

P oly. (NSISI-1)

'esolution +s $epth

! i s i M a i n

G o n e

Thic%ness 9m:

- r e s h / a t e r ! a n d

%rtifact


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%rtifact

2o4 tie

%natomy !eismic dan !caling


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%natomy !eismic dan !caling

,eismic and /oise


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,eismic and /oise

• Maor features of a seismic record (continued) Ground 'oll

= Tye of coherent noise

= Bo& fre>uency = Couled to surface or near$surface = 0elocity rangeD 35++$55++ ft?sec

%ir /ave = Tye of coherent noise = ;igh fre>uency = Travels through air = 0elocityD 11++ ft?sec 933+ m?s:

Multiple = 8esults from energy that becomestraed in shallo& layers

= ;as more moveout than rimaryreflections at same time

= ,urface multileD surface is oneboundary traing energy

=


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,ource$enerated /oiseD

• 8everberations 3 multiple reflections in the4ater or near surface layer

• Multiles 3 events 4hich follo4 a primary

reflection path plus multiple reflections in

one or more layers


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8ecord 3+8ecord 6

A &ea% reflector

strong reflector

C1 = C2 faulted

reflector

7ault is u to the

right

' ground roll! lo&fre>uency and

disersed

'ee &ater marine

A direct arrival

&ater bottom reflection

C shallo& rimary

reflection

M &ater bottom multile

-B eg$leg multile

associated &ith reflector C

Filma"! !eismic $ata %nalysis! 0ol 1! 6($)1

D anbom Geophysi cs


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Comparison of short-path and long-path multiples.

D anbom Geophysi cs


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irst!the tri"ial for this audien#e $ the PP C%P gathe


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#hat is /oiseG

#hat is /oiseG


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#hat is /oiseG

• oise is anything not related to primary subsurfacereflection.

• %ll noise is coherent if ade>uately sampled.

• !eismic programs are usually designed to correctlysample reflections. oise is often under sampled

and difficult to remove in processing.

#hy do &e care about noiseG


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#hy do &e care about noiseG

• /oise obscures or interferes &ith signal

• /oise limits the effectiveness of some rocesses 9e.g. $ migration!

deconvolution! velocity analysis:

• /oise detracts from the fidelity of rocessing oututs

,eismic and /oise


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,eismic and /oise

• Reflections are signal !

the rest is "noise#

%c>uisition and processingenhance reflection energy and

suppress the noise

Geophone arrays can attenuate

surface noise

'ecording system filter settings

can remove fre>uencies dominated

by noise

• Maor features of a seismic record he earliest event is called the

?-irst 2reak@

=,mall offsetsD direct &ave fromsource to receiver

= Barge offsetsD refracted &ave

Effset

T i m e

Multile

8 e f l e

c t i o

n s

7 i r s t A r e a % 6 r o u n d 8 o l l

A i r

# a v e

*onclusion


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*onclusion

Most seismic reflection techni>ues uses only compressional 4aves3 Easier to ac>uire3 'esolution, data >uality generally better 3 More sensitive to fluid properties

&se of shear and converted 4ave data is increasing3 May give a good image 4here compressional data cannot3 !ensitive to porosityR insensitive to pore fluid3 *ombined 4ith compressional data, tells more about rock and

fluid properties 33 (oissons 'atio

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Basic Seismic Interpretation

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