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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