Presentasi Ta Nadia Corinna Raissa

8/18/2019 Presentasi Ta Nadia Corinna Raissa

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ANALISA PERBANDINGAN METODE FILTER SRME DAN

FILTER RADON UNTUK DATA SEISMIK LAUT DANGKAL,STUDI KASUS: LAUT MADURA

By: Nadia Corinna Raissa


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OUTLINE

• INTRODUCTION

• BASIC THEORIES

• METHODOLOGY

• RESULTS

• CONCLUSION


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INTRODUCTION

• Background

• Purpose of the work:

• To result the subsurface marine seismic section withsign of multiple reduction using SRME and radon filter

before the interpretation level.

• To acknowledge the difference between SRME and

radon filter in multiple reduction of seismic shallow waterdata and to understand which one is better in this case.


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A FEW CALCULATIONS FOR GEOMETRY

Source

NEAR TRACE

OFFSET

(NTO)

NEAR TRACE

GROUP 1 / TRACE 1

FAR TRACE OFFSET (FTO)

((Number of groups -1) x Group interval) + Near Trace Offset

FAR TRACE

GROUP n

Total ‘active’ streamer length

(centre near group-------------------------------------centre far group)

GROUP

INTERVAL

Streamer length = 4050 meter Number of fold = 81Number of channel = 324 Number of shot = 623Channel interval = 12.5 meter Sampling interval = 2 milliseconds

Shot point interval = 25 meter Length of records = 7 millisecondsSP EOL = 1001 SP SOL = 1623

Number of fold = (Number of Channel / 2) x (Channel Interval / Shot Point Interval)Number of shot = SP EOL (End of Line) – SP SOL (Start of Line) – 1 (to calculate interval)Streamer Azimuth 138 + 180 = 318

To put the trace of seismic data at the right position and elevationTARGET


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Amplitude Correction

Influenced factors of seismic amplitude:

• Source Power

• Spherical Divergence

• Variation of reflection coefficient to offset and incident angle

• Attenuation and Absorption

• Multiple

• Diffraction

• Interference and Superposition• Geophone Sensitivity

• Instrument Balance


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TAR (True Amplitude Recovery)

Steps in seismic processing to compensate forattenuation, spherical divergence and other effects

by adjusting the amplitude of the data.

Simply said as:

A Tool to Recover The Amplitude

Recover decreasing amplitude due to the bellow factors

during seismic waves travel through the earthTARGET


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Noises on 2D Marine Data

Direct wave

Low frequencyNoise

DiffractionMultiples

Unmigratedreflector


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Noise Attenuation


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Dekonvolusi adalah suatu proses untuk menghilangkan wavelet seismik sehingga yang tersisahanya estimasi dari reflektifitas lapisan bumi atau dengan kata lain adalah suatu proses untuk

meniadakan konvolusi

Metoda Decon

Deterministik Statistik

Predictive DeconSpiking Decon *

WAVELET

RECORDED

SEISMIC TRACE

DECONVOLUTIONSpiking/Predictive Decon

Filter Wiener Predictive Filter


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MULTIPLESVarious Type of Multiples

S R

a

S R

b

S R S R

c

S R

d

S R S R

e

S R S RS R

c

Water-bottom multiples Free-surface multiples

Peg-leg multiples

Peg-leg multiples

Intrabed multiples Interbed multiples


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VELOCITY ANALYSIS

Beberapa pengertian kecepatan di dalam istilah seismik

Kecepatan sesaat V (instantaneous veloci ty )adalah laju gelombang yang merambat melalui satu titik dan

diukur pada arah rambatan gelombang, ditulis sebagai

Kecepatan interval V i (interval velocity )

adalah laju rata-rata antara dua titik yang diukur tegak lurus

terhadap kecepatan lapisan yang dianggap sejajar, ditulis

atau menurut rumusan Dix,

Kecepatan semu V a (apparent velocity )

adalah laju gelombang yang merambat sepanjang bentang

perekaman, misal pada sistem lapisan miring (ξ), maka

c = sudut kritis V 1 = kecepatan sebenarnya

Kecepatan rata-rata adalah perbandingan jarak vertikal z f terhadap waktu

perambatan gelombang t f yang menjalar dari sumber ke

kedalaman tersebut, ditulis

Kecepatan RMS

adalah kecepatan total dari sistem perlapisan horisontal dalambentuk akar kuadrat pukul rata. Apabila waktu rambat vertikal

t 1, t 2 , … , t n dan kecepatan masing-masing lapisan V 1,

V 2 , … , V n, maka kecepatan rms-nya untuk n lapisan adalah

Kecepatan stacking (stacking veloci ty atau VNMO)

adalah nilai kecepatan empiris yang memenuhi dengan tepat

hubungan antara T x dengan T o pada persamaan NMO,

Kecepatan migrasi (migrat ion veloci ty )

adalah nilai kecepatan empiris yang memberikan hasil terbaik

ketika digunakan dalam perhitungan migrasi.

dt

dz

t

z V

t

0lim

t

z V i

1

1

2

1

2

2

nn

nnnn

it t

t V t V V

c

a

V V

sin

1

f

f

f

f

f

f

f

f f

t

z

t

t V

V

n

k

n

k

k k

rms

t

t V

V

1

1

2

2

22

NMO

o xV

xT T


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MULTIPLE SUPPRESSION

(RADON FILTER)

Radon Filter is most commonly used for suppression of multiples.

To remove the water bottom multiple from seismic data

especially for marine data at the domainTARGET

p


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RADON FILTER

A

B

C

A’

B’

C’

= t - px

+ p

Hyperbola in T-X

map to ellipses in

- p

Linear events in T-

X map to single

points in - p

Plane wave

P=0

Tau represents intercept time at zero offset. P represents dip. The larger the dip of an eventin the X-T domain the higher its P value in the TAU-P domain. Flat events (our primaries)

appear around P=0 in the Tau-P domain


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SRME

• SRME is a powerful demultipletool because it requires no

velocity information, we are able

to use SRME with onboard

processing, and prior to radon

demultiple, to help improvepreliminary velocity analysis.

• Its ability to handle all of the

energy generated from the free

surface allows us to remove eventhe most complex diffraction

multiples with SRME, and an

iterative scheme permits its use in

shallow and deep water settings.

To remove the multiple energy including those energies that

techniques such as radon and Tau-P fail to addressTARGET


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Stack Principal

migration

d e c o n v o l u t i o n

CMP (X,Y)

OFFSET

TIME


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MIGRATION

Migration Principal Migrasi Antiklin

Migrasi Sinklin

Before

Before

After

After


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MIGRATION

Which Migration to use?


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METHODOLOGY


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Modul Radon


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Radon Picking Multiple (before interactive radon analysis)


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Radon Picking Multiple (after interactive radon analysis)


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Data Shot Gather

Koreksi NMO preprocessing Koreksi NMO filter radon


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Modul SRME


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Near Match Filter


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Middle Match Filter


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Far Match Filter


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Semblance Velocity Analysis

Preprocessing Radon SRME


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Stack Preprocessing


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Stack Radon

k


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Stack SRME

S k R d d SRME


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Stack Radon dan SRME


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CONCLUSION

• Pada data seismik laut dangkal ini, metode filter radon

lebih menunjukkan reduksi multipel yang lebih signifikan

dibandingkan dengan metode SRME.

• Pada pengolahannya, metode radon lebih praktis

daripada metode SRME.

• Filter radon lebih baik dalam menghilangkan multipel

pada far offset, sedangkan SRME pada near offset.


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THANK YOU

• Q & A SESSION

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