SEISMIK-STRATIGRAFI
1.
CONTENTS:
PENDAHULUAN (keberadaan data Seismik refleksi)
2.
PARAMETER REKAMAN SEISMIK REFLEKSI TERHADAP
GEJALA GEOLOGI
3.
HUBUNGAN ANTARA, BIDANG PERLAPISAN &
KARAKTER/ PARAMETER SEISMIK REFLEKSI
4.
GENESA & POLA PENGISIAN CEKUNGAN
BERDASARKAN SEISMIK REFLEKSI
5.
CIRI & GEJALA SIKUEN PENGENDAPAN
6.
PROSEDUR INTERPRETASI SERTA MAKNA, KARAKTER
UNIK REKAMAN SEISMIK REFLEKSI
7.
KOMPONEN-KOMPONEN KRONOSTRATIGRAFI &
PRESENTASINYA
8.
PETA FASIES BERDASARKAN DATA SEISMIK REFLEKSI
9.
PETROLEUM SYTEM & DHI, BERDASARKAN DATA
Tujuan Instruksional Khusus (TIK)
1. Setelah menyelesaikan pertemuan I & ke II, mahasiswa mampu
menjelaskan keberadaan data seismik refleksi
2. Setelah menyelesaikan pertemuan ke III, mahasiswa mampu
menjelaskan parameter rekaman seismik refleksi terhadap gejala
geologi
3. Setelah menyelesaikan pertemuan ke IV & V, mahasiswa mampu
menjelaskan hubungan antara, bid perlapisan & karakter/ parameter
seismik refleksi
4. Setelah menyelesaikan pertemuan ke VI & VII, mahasiswa mampu
menjelaskan genesa & pola pengisian cekungan berdasarkan seismik
refleksi.
5. Setelah menyelesaikan pertemuan ke IX & X, mahasiswa mampu
menjelaskan ciri & gejala sikuen pengendapan
6. Setelah menyelesaikan pertemuan ke XI & XII, mahasiswa mampu
menjelaskan prosedur interpretasi serta makna, karakter unik
rekaman seismik refleksi
7. Setelah menyelesaikan pertemuan ke XIII, mahasiswa mampu
men-jelaskan komponen-komponen kronostratigrafi &
presentasikannya
2. PARAMETER REKAMAN SEISMIK
REFLEKSI TERHADAP GEJALA
GEOLOGI
1. Makna Rekaman Seismik Refleksi, (Basic Seismic
Observations)
1) Sedimentary reflections . 2) Unconformities . 3)
Non-sedimentary reflections . 4) Artefacts & artificial
reflections
2. Parameter
Refleksi
(individu
& unit) 4) Spacing
• 1) Amplitudo,
2) Polaritas,
3) Kontinyuitas,
atau Frekuensi Refleksi, 5) Interval Velocity
• Reflection geometries: Reflection Terminations,
Reflection Configuration, External Forms
3. Perubahan Litologi, Diagenesa, Kandungan
hidrokarbon
1. Basic Seismic Observations
4 major groups of systematic reflections are distinguished on seismic sections
1.
2.
3.
4.
Sedimentary reflections representing bedding planes.
Unconformities or discontinuities in the geological record.
Non-sedimentary reflections; like fault planes, fluid contacts etc
Artefacts; like diffractions, multiples, etc..
Normal sedimentary reflection
Cross cutting side swipe
reflection
Listric fault plane, which
is in part also reflective
Hc fluid contact in
a reservoir sequence
Difraction curves on stacked Migration smiles on a migrated
seismic section
seismic section
TWT msec
1. Sedimentary Refections
• Seismic stratigraphy is the observation that individual sedimenttary
reflections can be considered timelines.
• This timeline concept equally signifies that seismic reflections tend to cross
laterally through different depositional environments & therefore they can
incorporate various lithofacies units.(geological sense)
• Seismic reflections passing continuously from a top, fore to a bottomset
confi-guration. In a geological sense it means going from a sand-prone shelf
(vcs_z-vfs_z), into a shale-prone slope (clay-z)& finally ending up in the
L-Boundary
U-Boundary
2. Unconformities (UNC)/ discontinuities
• Erosional
truncation, …..?
• Toplap …?
Erosional
truncation
Toplap
Concordance
• Concordance, …?
Time line≈ reflection
line≈ stratal line≈
time stratigraphic unit
Onlap
Downlap
Concordance
• Unc are surfaces of erosion &/or non-deposition which constitute time-gaps
in the geological record. Unc generate reflections because they separate
beds with different physical properties
• Strata below the unc are older & the beds overlying the surface are younger
than the time-gap. So the strata between 2 unc form a time stratigraphic
unit.
• Reflections generated by unc are representing a hiatus in the sedimentation
record & are normally diachronous. An unc coincides with a change in
structural dip of the units above (U) & below (L) the interface
• Several types of reflection relationships are distinguished at these uncon-
An example of erosional truncation, toplap,
concordance
0
1.0
Erosional truncation
Toplap
Concordance with
subtle indications
for sediment bypass
If the configuration displayed by the upper sequence is considered, the following reflection relations are distinguished
• Onlap whereby the younger sediments are progressively overstepping each
other
• Downlap in case of foresetting abutting on an unc. The younger strata are
depositio nally inclined. The inclined foresetting gives an indication for the
direction of the sedi ment supply. Starved sedimentation conditions prevail in
the distal area.
• Concordance if the overlying sediments show the same deformation as the
separat ing interface & the underlying unit
An example of onlap & down lap reflection
configurations.
Onlap
Dowlap
The unc represents a
depositional gap in the
geologic record. If it
has a regional
significance it is
considered a
depositional SB.
Interpretation of the
reflection terminations
as indicated by blue
arrows & defining unc
(red lines) which are
basically sedimentation gaps.
Non-sedimentary Reflections;
1.0
2.0
Evidence for subaerial erosion with an
important time hiatus. Peneplanisation
occurred before the younger sediments
were deposited
0
1.0
Submarine currents can cause
considerable local erosion. Note the
concordant contact lateral away from
the submarine canyon fill
Several characterristics are deduced from
unc type:
•the
Subaerial,
submarine, fluvial or glacial in origin The time gap is either erosional or non-depositional; the latter is indicating sediment bypass.
• The topographic relief is planar, irregular or with a certain inclination.
• The significance is either regional or local.
• The degree of tectonic deformation gives an idea about the rate of
instability of the region.
• In special cases information is deduced on the relative sea level behaviour,
sediment supply & rates of subsidence changes.
Jenis hubungan ketidakselarasan (Unconformity)
1. Basal unconformities,🡪 ketidakselarasan dng FR berkomposisi bat dasar
kristalin. (≈ nonconformities
2. Angular unconformities (ketidakselarasan menyudut) 🡪 ketidakselarasan
dng FR tersusun oleh lapisan2 yg mengalami deformasi scr struktural yg
su-dah terkikis/ tertoreh
3. Disconformities,🡪 ketidakselarasan dng FR mengalami erosi, ttp lapisan2
tsb belum mengalami deformasi scr struktural
4. Non-depositional Unconformities🡪 ketidakselarasan tanpa adanya erosi
pd FR, termasuk di dlmnya hardgrounds, carbonate platform slope, dll
Jenis Ketidakselarasan
1.
2.
3.
Non-UNC
Ang-UNC
Dis-Confor
Para-Confor
Non-conformity
Angular unconformity
Dis-conformity
Non-sedimentary reflections; like fault planes
1.0
3.0
3.11:
1.0
?
3.0
3.10:
Partly reflective listric fault plane,
with strong rotation & tilting of the
hanging wall sediments in respect to
the sub-// foot wall deposits.
Note that the oblique dip of the
reflections are here tectonically
induced & should not be confused
with sedimentary dips. Criteria to
discriminate between the 2 distinct
origins is the rather uniform &
regu-lar character of the lateral thick
ness variation of the layers & the
presen-ce
of thefault
curved
fault
Non-reflective
plane
withplane.
clear
fault-related reflection
termina-tions. There is a regular
spacing to the faulting, indicating a
uniform stress pattern & lateral
continuity of the layers. The
deeper part of the section is rather
chaotic & characterised by
discontinuous reflections. The
curved fault planes sole out in this
Non-sedimentary reflections
Fluid contact in a reservoir coinciding with a v/ρ
con-trast that is sufficient to generate a seismic
0.5 reflection. The gas has a lower ρ & lower P-wave v than
the brine porefill. The amplitu de anomaly corresponds
BS
to a bright spot. It is caused by the presence of a class
1.0 3 AVO re-servoir. The flat spot is the result of the
FS
change in pore-fill, it corresponds to the gas/water
1.5 interface.
Paleo-Moho in outcrop (Mineral phase changes)
Alcaline basalts
Incipient oceanisation
Intracratonic rift
crus
t
Moh
o
lithospher
e
A
B
astenosphere
resistivity
35
Brittle
crust 1
Ductile crust 2
Brittle
Mantle 3
(olivin)
km
100
Top of
L-Velocity Z
Ductile mantle
4
C
Artefacts; like diffractions, multiples, etc.
Kesalahan pengikatan mrpkn hal umum pd interpretasi & dpt
terjadi akibat:
1. Kesalahan navigasi & survei. Survei daratan, mis-ties lebih jarang terjadi
di bandingkan survei di laut, dimana kesalahan penentuan posisi bisa
men-capai 100 m pd perpotongan lintasan,
2. Konvensi polaritas. Bila informasi mengenai polaritas rekaman tdk
diketa-hui dng baik, menyebabkan kesalahan pengikatan lintasan yg cukup
besar.
3. Masalah Pemprosesan. Koreksi statik, perbedaan (kecepatan staking, pola
muting, operator dekonvolusi, fasa dr wavelet, dsbnya), mrpk kemungkinan
penyebab kesalahan pengikatan. Bila kesalahan tsb terjadi pd 2 survei yg
berlainan, & konsisten, mk suatu static shift yg konstan dpt diterapkan.
4. Difraksi. Kesalahan pengikatan sering ditemui pd perpotongan lintasan
de-kat sesar kecil. Hal ini dpt disebabkan krn interferensi ant gel refleksi &
di-fraksi, terutama pd lintasan berarah miring thdp bid sesar dimana efek
di-fraksi tdk dpt dihilangkan dng baik.
5. Migrasi. Proses migrasi konvensional seismik 2-D juga mrpk penyebab
2. Parameter Refleksi (individu)
• 1) Amplitudo, 2) Kontinyuitas, 3), Spacing atau Frekuensi
Refleksi, 4) Polaritas 5) Interval Velocity
1. Amplitudo adlh ketinggian puncak (peak) atau
pa-lung (trough) refleksi, yg besarnya tergantung pd
RC. ( tinggi, sdg & rendah). Perubahan vertikal
amplitudo, digunakan untuk mengidentifikasi unc,
sdgkan peru-bahan lateral untuk identifikasi
perubahan fasies
seismik
2. Kontinyuitas
refleksi
mencerminkan konsistensi
kemenerusan lateral refleksi. Refleksi yg diskontinyu adlh
kelurusan yg menerus, ttp bgn yg menerus tsb terpotong oleh
suatu gap yg lebarnya ± 2 - 3 tras. Refleksi yg kontinyu mempunyai karakter yg menerus sepanjang jarak yg signifikan (km).
Derajat kontinyuitas dideskripsikan sbg sgt kontinyu hingga
dis-kontinyu. Kontinyuitas refleksi juga mencerminkan kondisi
pe-rubahan lateral IA (litologi). Refleksi yg diskontinyu
mencermin-kan lingk dimana terjadi perubahan lateral fasies,
mis pd sistem fluvial. Refleksi yg kontinyu mrpkan karakter dgn
kondisi peng-endapan lateral yg seragam terjadi scr ekstensif,
2. Parameter Refleksi (lanjutan)
3. Frekuensi refleksi adlh jmlh refleksi per unit waktu & dipengaruhi
oleh kombinasi efek interferensi & frekuensi sinyal seismik Gambar di
bawah ini menunjukkan contoh bhw karakter frekuensi refleksi dpt
digunakaan untuk memandu korelasi.
4. Polaritas refleksi sering dpt ditentukan dr hub onlap pd rekaman
ber-fasa min atau dr amplitudo maks rekaman berfasa nol.
Kombinasi polaritas & amplitudo dpt menjadi petunjuk jenis litologi yg
menyebabkan timbulnya refleksi. Cth, pd sekuen muda & dangkal,
batupasir Φ tinggi yg ditutupi batulempung dpt menghasilkan
amplitu-do sdg-tinggi dgn RC(-), sdgkan batulempung yg menutupi
batugam-ping masif akan menghasilkan amplitude tinggi dgn RC (+)
Polaritas & Seismic Trace
S-Eropa
(Min-Phase)
RC
Reverse
Normal
waktu
S- SEG
(Min- Phase)
S- Eropa
Standard SEG
(Zero Phase) (Zero Phase)
Litologi
• Seismic Trace adlh data seismik yg
te-rekam oleh 1 geophone, ini
mencermin- kan respon dr medan gel
elastik thdp kontras IA (reflektivitas) pd
batas lapisan btn sediment yg satu dgn
btn lainnya.
Polaritas
Normal - Reverse
Tdpt 2 jenis konvesi polaritas: Standar SEG &
Standar Eropa. Keduanya berkebalikan.
Gambar ini menunjukkan Polaritas Normal & Polaritas Reverse untuk sbh wavelet fasa
nol & minimum phase pd kasus RC meningkat (RC positif) yg terjadi pd contoh batas air
laut dgn dasar laut/ lempung.
AMPLITUDO
Discontunuity
2. Parameter Refleksi (lanjutan)
High
Contunuity
Low
FREQUENCY/ SPACING
High
Low
The Reflection Character of a Seismic Loop:
☞ R-Configuration, which is related to the geometry of the bedding pattern
resulting from specific depositional processes, the original paleo topography
& fluid contacts.
☞ R-Continuity, which describes continuity of the layers. It is directly related to
sedimentary processes & therefore also to the environment of deposition.
☞ R-Amplitude, providing a measure for the reflection strength, litholo- gical
contrast, bedding spacing & fluid contents.
☞ R_Frequency, which gives an estimation of the bed thickness & possibly
Parallel to Wavy – (Expression of Seismic Facies Unit)
.
Continuous, Low F, Low-Med A Continuous, L-F, M-H A
Discontinuous,H-F, H-A
Continuous,High F, High A
Chaotic
• a high amplitude (horizontal excursion of seismic wiggle from the time axis)
reflection character generally points to vertical alternation of contrasting
lithologies (e.g. sand/shale; carbonate layers in a shaley sequence).
• a low amplitude indicates more similar lithologies on both sides of the
inter-face (e.g. sand/silty shale).
• the frequency of a reflection (vertical separation on a seismic trace of a
seismic loop between two consecutive zero crossings) can give some idea
concerning the thickness of the beds. There are pitfalls when dealing with
thin bed interference effect
• The continuity gives information on the energy level of the deposits. a high
continuity suggests a great lateral extent of the same sedimentation
Unit Fasies Seismik di Endapan Paparan
Berdasarkan Parameter Individu Seismik pantul
H-Amplitude &
continuity
(interbedded
H&L energy)
L-Amplitude
(uniform
energy)
L-continuity,
variable amplitude
(variable energy)
Broad, low relief mound
variable amplitude &
continuity (variable
energy)
SFU’s on the shelf, which corresponds to a topset position on the
seismic data. Continui ty is related to energy level of environment
of deposition, while amplitude reflects inter-bedding of lithologies
Reflection Parameters & Gelogic
Significance
1.
Reflection Configuration
Bedding Patterns
Depositonal Processes
Erosion Paleotophography
Fluid Contact
2.
Reflection Continuity
Bedding Continuity
Depositional Processes
3.
Reflection Amplitude
Bed spacing
Velocity Dencitas Contrast
Fluid Content
4.
Reflection Frequency
Bedding Thickness
Fluid Content
5.
Interval Velocity
Estimation of Lithology
Estimation of Porosity
Fluid Content
6.
External Form & Areal
Assosiation of SF Unit
Gross Depositional Environment
Sedimen Source
Geologic Setting
Parameter Refleksi: Reflection
Geometries
EXTERNAL FORMS
REFLECTION
REFLECTION
TERMINATIONS
(at Sequence B)
CONFIGURATION
(With Sequence)
•
•
•
•
LAPOUT
− Baselap (onlap,
Downlap)
− Toplap
PRICIPAL STRATAL/
INTERNAL CONFIGURATION
−
−
−
−
TRUNCATION
− Erosional
− Structural
Pararel
Subpararel
Divergent
Prograding Clinoforms
Sigmoid, Oblique,
complex
sigmoid-oblique,
Shingled, hummocky
clinoform
− Chotic
CONCORDANCE
− No termination
− Reflection Free
•
MODIFYING TERMS
Even, Wavy, Reguler,
Uniform, Variable
Hummocky,,Lenticular,
Contorted, Distrupted
(At Sequence & Seismic
Facies Unit)
−
−
−
−
−
−
−
Sheet
Sheet Drape
Wedge
Bank
Lens
Mound
Fill
Prinsiple of Stratal/ Unit Termination
(≈ Reflection Terminations)
EROSIONAL TRUNCATION
OVERLYING
UNCONFORMITY
TOP-LAP
MARINE-ONLA
P
P
UNDERLYING
UNCONFORMITY
COASTAL
ON-LAP
INTERNAL
CONVERGENC
E
A
OFF-L
LAP
ONP
-LA
DOWN
BASE-LA
P
Sikuen Pengendapan (Depositional
Sequen-ces) adlh sbh unit stratigrafi yg terdiri
dr urut2an lapisan batuan yg relatif selaras &
• LAPOUT
scr genetik berhubungan & dibatasi di bag atas
− Baselap (onlap, & bawah-nya oleh bidang ketidakselarasan
Downlap)
(unconformi- ties) atau bid selaras yg sepadan
− Toplap
• TRUNCATION
(correlative conformities) dgn bid
− Erosional
ketidakselarasan tsb.
− Structural
REFLECTION
TERMINATIONS
(at Sequence B)
•
CONCORDANCE
− No termination
Didlm tubuh sikuen pengendapan tsb, dicirikan
dgn adanya pola perlapisan (Stratal, ≈ Reflec-
Hubungan antara Bidang Perlapisan &
Batas Sekuen Pengendapan
• Lapout adlh pola pemberhentian (terminasi) lapisan (≈ reflection
pattern) secara lateral dengan batas pengendapannya. Terminasi tsb
dpt terjadi di bawah (base-lap) atau di atas (top-lap) suatu sekuan
pengendapan. Toplap mencerminkan nondepositional/ hiatus
(correlative conformities), sedangkan erosional truncation
mencerminkan bidang erosi. (Unconformity)
• Onlap adlh pola pemberhentian di sekuen bagian bawah, dimana
pemberhentiannya terjadi di bagian up-dip nya. Bila
pemberhentian-nya terjadi dibagian down-dip disebut downlap
• Proximal onlap yi; onlap pd arah sumber sedimen & Distal downlap
yi: downlap pd arah yg berlawanan dr sumber sedimen, umumnya
mrpkn indikasi dr permulaan & akhir dr penye-baran secara lateral dr
pengendapan. Onlap & downlap umum-nya lebih mencerminkan
non-depositional hiatus drpd erosional hiatus.
• Truncation-lap adlh terminasi scr lateral suatu perlapisan. Aki-bat
terpotong dr batas pengendapan aslinya.
Hubungan antara Pola Perlapisan &
Konfigurasi Pola Refleksi di dalam Sekuen
Pengendapan (Seismik Facies Unit)
•Analisa fasies seismik adlh deskripsi dr
parameter refleksi (al: konfigurasi,
kontinyu-itas, amplitudo, frekuensi &
• PRICIPAL STRATAL/
kecepatan in-terval), untuk interpretasi
internal CONFIGURATION
geologi
− Pararel
•Sebuah unit fasies seismik adlh suatu unit
− Subpararel
seismik yg tersusun oleh kumpulan pola
− Divergent
− Prograding
Clinoforms refleksi yg mempunyai parameter berbeda
Sigmoid, Oblique,
dgn unit fasies di sekitarnya (Mitchum dkk.,
complex
sigmoid-oblique,
1977). Dimana setiap parameter dpt
Shingled, hummocky
mem-berikan informasi yg mengenai kondisi
clinoform
geologi
− Chotic
•Konfigurasi internal sekuen seismik adlh
− Reflection
Free
Even,
Wavy, Reguler,
: parallel, subparallel, divergent, chaotic,
Uniform, Variable
• MODIFYING
TERMS
Hummocky, Lenticular,
reflection-free, mounded, sigmoid, oblique,
Contorted, Distrupted
complex sigmoid-oblique, shingled,
REFLECTION
CONFIGURATION
(With Sequence)
Parallel-even
Parallel-wavy
Sub-parallel
Tangential obliqe
Divergen
Complex Sigmoid/ oblique
Sigmoid
Shingled
Parallel oblique
Chaotic-no stratal pattern
Hummocky clinoforms
Chaotic-deformed
Reflection Free
Distruped
Contorted
Lenticular
Internal Reflection Configuration (IRC)
• IRC Paralel (a,b) & Subparalel (d) menunjukkan kecepatan
pengen-dapan yg konstan pd suatu paparan yg subside scr seragam
atau pd basin plain yg stabil. Umumnya ini berasosiasi dgn bentuk
eksternal: sheet, sheet drape, fill
• IRC divergen (c) dicirikan oleh bentuk wedge dimana penebalan lateral
lebih disebabkan oleh penebalan dr refleksi itu sendiri bukan krn onlap,
toplap atau erosi. Mencerminkan variasi lateral kecepatan pengendpan
Divergent Internal Reflection Configuration
• DIRC are found in wedge-shaped sediment bodies,
where the sediment thick ness distribution is asymmetric.
Obviously important lateral thickness variations do exist.
• These geometries can be due to variations in sedimentation rates, subsidence &/ or burial effects (differential compaction).
• The internal reflection terminations occur randomly & don’t coincide with a
distinct SB. The divergent geometry indicates syn-depositional differential
tectonic movements.
Clinoforms or foresets IRC
• The shape & angle of repose of sediment on
these slope systems is influenced by : 1)
Com-position of the deposited material, 2)
Sedimen-tation rate & quantity of sediment input.
3) Sali-nity of the water, 4)Water depth, 5)Energy
level of the environment of deposition, 6)
Position of the sea-level, which is closely related
to the base-level profile, 7) Subsidence rate.
• Under ideal conditions the clinoforms display a
topset, foreset, bottomset relationship
Sigmoid
topset
fore
set
bottomset
Complex Sigmoid/ oblique
Tangential obliqe
• IRC sigmoid (a)
mencerminkan proses agradasi
yg menerus, segmen atas
sejalan dgn progradasi bag
tengah akibat suplai sedi-men
yg relatif pelan pd basin yg
relatif subsiding scr cepat
dan/atau cepatnya kenaikan
m.a.l. shg terbentuk
pengen-dapan unit bag atas.
Mereflek-sikan regim
pengendapan energi rendah
• IRC parallel oblique (c)
mem-punyai kemiringan yg
relatif lbh besar,
mencerminkan energi
pengendapan yg lebih tinggi.
• Complex sigmoid-oblique
(d) perselingan antara o & s
IRC Progradasi (: sigmoid, oblique,
complex s-o, shingled & hummocky.
Terbentuk akibat pertumbuhan
pengen-dapan scr progresif lateral dr
bid pe-ngendapan yg miring, (clinoform)
• IRC shingled mencerminkan
progradasi fasies ke dalam air
dangkal.
• IRC hummocky clinoform
mencerminkan progradasi
lidah clinoform ke dalam air
Di
fferent Types of Foresets
• Oblique,. This area is mainly an area of
sedi-ment by-pass. This type of f-setting
represents a somewhat h-energy slope system
& coarser deposits may be incorporated in
these f-sets. The little developed b-sets do
suggest that the fall-out of debris was rather
drastic & limited in areal extension. Starved
Oblique Progradational
(high-energy)
sediment conditions reign on the distal part of
the basin floor.
Occasionally it may also point to the presence of contour currents that rework
the material at bottom of the slope & transport them further away. The top-lap
geometry indicates a rapid fall of relative sea level at the onset of the next
d-s. The sedimentation mechanism is most probably traction (bedload
transport) & suspension related (gradual fall-out or hemi-pelagic).
• Parallel oblique, which points to little change in direction of the prograding
slope. It also means a rather uniform filling in of the basin, as a lot of switching of depocenters would result in different progradation directions. This
geo-metry normally also reflects a h-energy slope system
• Tangential oblique, whereby the b-sets are well developed. This type of
f-sets points to a very efficient transport mechanism for the sediments over
the shelf area & the spreading out of material over vast basinal areas. Most
likely the sediments are deposited from suspension, but also turbidity currents
can bring material directly to deeper parts of the basin (fig 3.24)
Different types of foresets (lanjutan)
• Sigmoidal, whereby the t-set & b-sets are
pre-served. Its geometry does suggest a relative
rise in sea level, with a reasonable sediment
supply. This geometry also might point to deposi
tion from suspension (partial sediment drape). It
represents there fore a L-energy slope system.
Sigmoidal Progradtional
(low-energy )
• Shingled, which is characterised
by a much smaller f-set height.
This type of low-angle f-setting is
found in both a t-set as well as in a
b-set position. It is interpreted
either as shallow marine progradation in a H-energy environment or
as deep marine progradation on
the basin-floor. In the deeper
mari-ne basin this shingling may Fig Progradational reflection geometry at 1.0
&1.5 sec TWT. The progradation is oriented
point to the importance of mass
from right to the left & it represents the
flow se-dimentation. It may
out-building of a basin margin (>2 km paleo
indicate accre-tion in submarine
waterdepth). Note the drastic scale
fans or contour current mounds
diffe-rence with the previous GPR figure. A
(contourites). No straight for ward
ma-jor unc is present in the Tertiary
overbur- den, an expression of the
water-depth con-notation is
Hummocky Reflection Configuration
HR configuration consists of irregular, discontinuous reflections with variable
amplitudes. It is characterised by little systematic reflection terminations. It can
occur both in t & f-set positions. It indicates the presence of cut-&-fill geometries
&/or contourted bedding. The contourted bedding is the result from water
esca-pe during early burial & compaction. It is characterised by oversteeping of
the sedimentary laminations. Other water escape features are dish & pillar
structur-es of the time the cut-&-fill is interpreted as channelised deposits
Shingling/channel accretion
200
240
TMT msec
220
200
Hum
mocky
220
240
Hummocky seismic facies characterised by short, curved & discontinuous reflections.
Often it can be interpreted as the result of a cut-&-fill sedimentation pattern.
Prograding Shelf-Slope System
18
20
22
24
26
28
30
32
34
36
0.0
0.4
0.8
1.2
1.6
2.0
Top-, fore- & bottom set relationships. Generally seismic reflections do cross several depositional
environments. In the subsurface the coarser shelf sediments are gradually replaced by more
shale-prone slope sediments without generating a distinct seismic response. Constraints in the
horizon-tal resolution don’t always favour the detection of individual lateral sand pinch outs
Subtle low-angle progradation or shingling, that can be difficult to outline. Trans
port directions are quite different in the Ordovician Ghudun & Safiq fm.
Sometimes sections are flattened on a specific horizon. It may help to
compen-sate for the effects of the later tectonic deformation & facilitates the
interpretation of paleo geomorphologic features.
Chaotic Reflection Configuration
IRC chaotic : produk dr sistem
pengendapan energi tinggi, atau
akibat deformasi kuat. Dpt
mencer-minkan slump structures,
cut & fill channel, daerah lipatan
atau terse-sarkan scr kuat.
IRC reflection free mencerminkan
tubuh batuan beku yg besar &
ma-sif, kubah garam, tubuh
batupasir atau shale yg homogen
dan
tebal reflections of variable
CRC are composed of discontinuous
discordant
ampli-tude & frequency. The discontinuous character suggest a highly
discordered internal organisation of the deposits. It occurs in all kind of DE &
may represent: • Channel fills in a proximal fan. •Slumped deposits on a
slope. • Olisto-stromes • Overpressured shales • Volcanic rocks • Mobile
salt deposits
Chaotic Reflection Configuration
Chaotic SFU, interpreted as olistostrome
deposits in the Guadalquivir Basin, which
is foreland basin created in response to
progressive nappe emplacement in the
Betic Cordilleras located to the south.
Low-angle foresetted turbidites of
Depo-sitional-Sequence V are
downlapping on the chaotic
mega-slumps. These sand-prone
turbidites are gas bearing.
Chaotic discontinuous SFU due
to presence of deformed over
pressured shales resulting from
improper dewatering during rapid
burial of the sediments.
Chaotic Reflection Configuration
0.0
1.0
2.0
3.0
0.0
Seafloor
OLIGOSEN-RECENT
EOSE
N
1.0
PLUG
Chaotic facies
dis-played by
volcanic rocks shape
& high-amplitude top
boun-dary.
Gravimetrics &
magnetics support
the volcanic origin. It
is a volcanic centre,
active on the
Paleo-cene–Eocene
time boundary.
2.0
3.0
Contemporaneous volcanic activity & rifting has been reported from Eastern
Greenland. From here volcanic ashes were wind-blown & deposited over
large parts of the North Sea basin. These ashes form an important regional
seismic event, known as the Thulean Tuff marker. Reworking by other
1
k
m
3
5
k
m
1
3
5
(a) Grounded salt pillow with internally a chaotic sfu. Note that the overburden
tectonics is detached from the deeper structures & the salt layer acts as a
decollement unit.
(b) Zechstein salt diapir that shows an internal chaotic sfu & associated with
severe deformation of the overlying beds. The overburden shows some
Reflection Free Zones
RFZ areas coincide with zones
where AI contrasts are weak or
lacking. This implies a rather ho
mogene gross lithology; it can
be thick shales, limestones,
sands, etc. Massive reefal build
ups & even igneous bodies
so-me times appear RFZ.
Intensely tectonised deposits
like salt dia-pirs & volcanic
intrusives may also show a RFZ
facies
Carbonate build-up with several
SFU. The high-energy reef front
is characterised by lower
amplitu-de chaotic reflections.
Note that the gas containing
re-servoir section is represented
by a high amplitude SFU (bright
spot).
Low reflective to hummocky
reflections in basalt body
Volcanics in The Irish Sea
Low reflective to hummocky SFU originating from a lenticular igneous body.
Its presence is confirmed by the measured gravity data. The deeper seated
time structure are partly caused by a pull-up effect, due to the velocity
con-trast between the basalt a& the Tertiary sediments (6000 m/s versus
2800 m/s). This effect will disappear when a proper time-depth conversion is
done.
External eflection Configuration (ERC)
Sheet-Drape
(L-Energy)
Slope-Front Fill
(L-Energy)
Onlap-Fill
(Usually Energy)
• ERC sheet, wedges, banks umumnya terbentuk pd
fasies paparan.
• Sheet drape mencerminkan pengendapan yg
sera-gam, & berenergi rendah pd laut dalam.
• Lens form, berasosiasi dgn progradasi clinoform.
• Mound form, berasosiasi dgn deep sea fans, lobes,
slump masses, contourite, carbonate buildup, reefs,
volcanic mound.
• Bentuk fill dicirikan oleh lapisan yg mengisi permukaan di bawahnya yg mempunyai relief negatif &
ber-asosiasi dgn erosional channels,
canyon fills,
Various external
structu- ral-trough fills, fans,geometries
slumps, dll of SFU in
slope & basinal areas
Mounded Onlap Fill
(H-Energy)
Fan-Complex
(H-Energy)
Chaotic-Fill
(Variable Energy)
Contourity
External Geometry of SFU
The morphological external shape of the units are described in terms
of:
☞ Sheets or sheet drapes, which point to uniform sedimentation
con-ditions in the basin & vary little differentiation of environment of
de-position. The associated SFU is sub-parallel to wavy & undulating.
Generally these drapes are composed of fine-grained deposits with
sedimentation out of suspension.
☞ Wedges, which indicate a sudden break in the sedimentation pattern.
Internally it represents a gradual differentiation in environment of
de-position & a lateral change in sedimentation rate.
☞ Banks or monoclines, which point to substantial differentiation in the
sedimentation pattern. They have an elongated shape. Locally higher
energy conditions exist. Often foresetted internal geometries are
detected.
☞ Mounds, which represent 3D depositional buildups. They indicate
•higher
Carbonate
build-ups
together in
with
their
talusMounds
deposits.are interpreted as:
energy
environments
the
basin.
• Submarine fan complexes.
• Contourite deposits resulting from thermohaline density currents.
• Volcanic eruption cones.
Contoh2 bentuk mounded (external form of the mounded)
Fan Complex Simple Fan Complex Compound
Contourite Mound
Migrating Wave
Slump
Volcanic Mound
CARBONATE MOUND
Pinnacle
with Velocity pull-up
Homogeneous
with drape
Homogeneous with
difractions
Bank edge
with
velocity sag
Configurasi Basin Fill
(Reflection patterns in fills)
Bentuk fill dicirikan oleh lapisan yg mengisi permukaan di
bawah-nya yang mempunyai relief negatif & berasosiasi dengan
erosio-nal channels, canyon fills, structural-trough fills, fans,
Reflection
patterns in various sedimentary fills. Differential compaction effects
slumps,
dll
can give a clue on the contents of channel fills. The shale prone levees are
compacted much more than the sands. A convex upward bulge is therefore
probably indicative for sand prone sediments
Analisis Fasies Seismik (review)
∙
∙
∙
∙
∙
∙
̵
̵
̵
Batuan sedimen yg terbentuk pd berbagai lingkungan pengendapan tsb
(spt: channel sungai, sistem delta, kipas bawah laut, carbonate mound/ reef)
disebut benda geologi (≈gejala stratigrafi)
Gelombang seismik yg terefleksikan kembali ke permukaan akan
memberi-kan gambaran bentuk eksternal & tekstur internal dr benda2
geologi
Analisis fasies seismik adlh analisis bentuk eksternal & tekstur internal
benda geologi tsb dari penampang rekaman seismik.
Terdapat 8 jenis bentuk eksternal yi: sheet, sheet drape, wedge, bank,
lens, mound, fan & fill.(lihat gambar)
Dlm analisis fasies seismik, batas dr benda2 geologi diatas disebut reflection
terminations. (terminasi tsb memiliki karakter refleksi yg kuat/ amplitudo
refleksi yg cukup dominan).
2 jenis batas benda geologi (sequence seismic boundary), yi: batas atas
(erosional truncation & top lap) & batas bawah (onlap & downlap)
Erosional Truncation (unconformity) diakibatkan oleh peristiwa erosi krn
terekspos ke permukaan.
Toplap diakibatkan krn tdk adanya peristiwa sedimentasi & erosi.
Onlap, pd lingkungan shelf disebabkan krn kenaikan m.a.l relatif, akibat
Bentuk Tekstur Internal dr Benda2 Geologi
1
1.
Parallel: mrpkn pengendapan sedimen dgn rate yg seragam,
atau pd paparan (shelf) dgn subsiden yg uniform atau
sedi-mentasi pd stable basin plain.
2
2.
Subparallel: terbentuk pd zona pengisian, atau pd situasi yg
terganggu oleh arus laut.
3
3.
4
Subparallel between parallel: terbentuk pd lingkungan
tek-tonik yg stabil, atau fluvial plain dgn endapan berbutir
se-dang.
4.
Wavy parallel: terbentuk akibat lipatan kompresi dr lapisan
parallel diatas permukaan detachment atau diapir atau sheet
drape dgn endapan berbutir halus.
5.
Divergent: terbentuk akibat permukaan yg miring scr
pro-gresif selama proses sedimentasi.
6.
Chaotic: pengendapan dgn energi tinggi (mounding, cut & fill
channel) atau deformasi setelah proses sedimentasi (sesar,
gerakan overpressure shale, dll.)
7.
Reflection free: batuan beku, kubah garam, interior reef
tunggal.
8.
Local chaotic: slump (biasanya laut dalam) yg diakibatkan
5
6
7
8
Bentuk Tekstur Internal Tekstur yg
terprogradasi
1.
Sigmoid: tekstur ini dpt terbentuk dgn suplai sediment yg
cu-kup, kenaikan m.a.l relatif cepat, rejim pengendapan
energi rendah, spt slope, umumnya sediment butir halus.
2.
Oblique tangential: suplai sediment yg cukup sampai
besar, m.a.l yg konstan spt delta, sediment butir kasar pd
delta plain, channel & bars.
Oblique parallel: oblique tangensial varian, sediment
terpilah lebih baik.
1
2
3
3.
4
5
4.
Complex: lidah delta dgn energi tinggi, dgn slope
terprogra-dasi dalam energi rendah.
5.
Shingled: terbentuk pd zona dangkal, dgn energi rendah.
6.
Hummocky: terbentuk pd daerah dangkal tipikal antar
6
Bentuk Tekstur Pengisian Channel
1.
Onlap Fill: sedimentasi pd channel dgn energi relative
rendah.
2.
Mounded Onlap Fill: sedimentasi dgn energi tinggi.
Setidaknya terdapat dua tahap sedimentasi.
3.
Divergent Fill: shale prone yg terkompaksi dgn
sedimenatsi energi rendah, juga sbg tipikal tahap akhir dr
pengisisan graben.
4.
Prograded Fill: transport sediment dr ujung atau pd
lengkungan channel.
5.
Chaotic Fill: sedimenatsi pd channel dgn energi yg sangat
tinggi.
6.
Complex Fill: tdpt perubahan arah sedimentasi atau
perubahan aliran air.
1
2
3
4
5
6
Bentuk Tekstur Karbonat
1
1.
2
2.
3
3.
4
4.
1)
Bentuk tekstur Mounded
2)
1.
3)
Reflection free Mound: patch atau pinnacle reef; strata
me-nunjukkan sedimen miring yg lebih terkompaksi (mungkin
shale).
Pinnacle with Velocity Pull-Up: patch atau pinnacle reef,
dgn pertumbuhan bbrp tahap (multi stage), mungkin cukup
poros.
Bank-Edge with Velocity Sag: Shelf edge reef dgn porositas
yg sgt bagus, sediment penutupnya mungkin carbonate
prone.
Bank-Edge Prograding Slope: shelf edge reef yg
bertum-puk, tertutup oleh klastik, mengalami perubahan
suplai sedi-ment.
2.
3.
Fan Complex: penampang lateral dr kipas (fan) yg dekat dgn
sumber sediment
Volcanic Mound: margin konvergen pd tahap awal; pusat
4)
aktivitas
rifting pada rift basin
Compound Fan Complex: superposisi dr berbagai kipas.
Bentuk Eksternal Benda2 Geologi
sheet
Basin fill
fan
mound
Slope front fill
Channel
fill
1
3
lens
wedge
Sheet
drape
2
4
Batas Benda Geologi
(sequence seismic boundary)
1.
2.
3.
4.
Erosional Truncation
Toplap
Onlap,
Downlap
Bentuk Tipe2 Fasis Seismik
Basin Slope & Basin Floor
1
2
3
4
1.
Sheet-drape (low energy): seragam, pengendapan laut
da-lam yg tdk tergantung pd relief dasar laut, litologi
seragam, tidak ada pasir.
2.
Slope Front Fill: kipas laut dalam, Claystone & siltstone
(energi rendah)
3.
Onlap-Fill (low energy): pengendapan dgn kontrol gravitasi
(arus turbidit kecepatan rendah)
4.
Fan-Complex (high energy): diendapkan sbg kipas, mound
& slump, meskipun energi tinggi, mungkin masih
mengan-dung batupasir sebagai reservoar .
5.
Contourite (variable energy): biasanya sedimen butir halus,
tidak menarik unutk eksplorasi, bentuk tidak simetris, arus
tak berarah.
6.
Mounded Onlap-Fill (High Energy): fasies peralihan antara
chaotic & onlap fill, control gravitasi, reflector tdk menerus,
smkn menebal kearah topografi rendah yg menandakan
en-dapan energi tinggi.
7.
Chaotic Fill (variable energy): mounded, terdapat pd
5
6
7
Efek Perubahan
Litologi primer berasal dr batas perubahan nilai IA, akibat
•Refleksi
ada-nya perubahan litologi
•Perubahan unit/ jenis perlapisan dpt disebabkan: perubahan
pe-ngendapan, litifikasi, variasi suplai sedimen. variasi musim,
dll
•Jenis batuan sedimen genetik dpt dibagi menjadi 3 kelompok : 1)
Sedimen mekanis & 2) Sedimen kimiawi (garam & evaporit) atau
proses biologis (reef ). 3) Sedimen Organik (batubara)
•Proses pengendapan & transportasi sedimen, scr mekanis dpt
dikelompokkan: 1) butir yg tertransport oleh arus bedload, & 2)
butir yg tertransport oleh arus suspensi
‒ Btrn ukuran pasir, tergantung pd bentuk, bj nya, dll. Btrn memerlu-kan
batas kecepatan arus minimum tertentu, untuk dpt tertransport. Suatu
arus berkecepatan lebih tinggi dr batas miminum tsb, akan me
mindahkan btrn & kmd mengendapkannya, begitu nilai kecepatan-nya
dibawah batas tsb
‒ Btrn ukuran lempung. Btrn memerlukan kecepatan relatif tinggi,
curren
t
Shallow water current & wave
activity
Strom wave
base
Still
water
100 m
Sedimentation from
suspension
Longest time gap
Onlap onto edge of clastic body
increasing gap
4
increasing time gap
shortest time gap
llustrasi hub bentuk pengendapan sedimen butir halus & kasar & Sketsa menunjukkan bgmn
bentuk tubuh sedimen klastik dpt mempengaruhi proses sedimentasi (Badley, ‘85).
• Krn variasi arus kecepatan, ini mempengaruhi kecepatan pengendapan btrn
pasir & lempung, mk bila episode pengendapan klastik berhenti & daerah tsb
kembali mengalami pengendapan dr arus suspensi, akan didpt topografi dasar
cek yg baru menutupi sedimen sebelumnya, shg membentuk pola se-kuen off
laping-onlapping
• Endpn btrn lempung, akan onlapped dg btrn pasir, & rumpang waktu antara
edpn pasir & lempung di atas satuan pasir akan lebih besar drpd yg di daerah
cek
• Perubahan lateral dr endpn pasir menjadi lempung, mempunyai arti penting dr
se-gi litologi & implikasi waktunya. Arti penting skala waktu pd bid perlapisan tsb,
Efek Perubahan Litologi (lanjutan)
• Ref-seismik, dihasilkan dr batas atas & bawah unit lap & cenderung mengikuti
suatu kombinasi dr grs & rumpang waktu. Bila terdpt struktur internal yg
ber-skala signifikan (mis klinoform), refleksi & bid atas maupun dasar akan
meng- ikuti ketidakselarasan.
• Refleksi mengikuti batas litologi, bukan batas fasies. Perubahan lateral fasies
umumnya mencerminkan perubahan amplitudo, bentuk gel, frekuensi &
konti-nyuitas.
• Bila suatu unit klastik yg tebal membentuk kipas bawah laut, mk refleksi dr bid
permukaan atas & struktur internal akan mengikuti rumpang waktu,
sedang-kan refleksi & batas bawah interval turbidit klastik akan mengikuti grs
waktu.
• Pd lingk klastik dangkal, kebanyakan unit individual sgt tipis shg terletak antara ketebalan tuning & detectable limit. Oleh krnnya perubahan ketebalan
ha-nya akan mempengaruhi amplitudo refleksi.
• Pd sekuen argilit, refleksi dihasilkan dr interferensi & akan paralel dng grs
waktu, umumnya berkontinyuitas sdg-baik. Amplitudo cenderung sdg-buruk.
Pola refleksi divergen, mrpkn indikasi dr endpn btr halus. Tdk jarang kontras
IA sgt rendah shg menunjukkan gejala reflection free. Pola refleksi caotik
ter-jadi akibat slumping, aliran akibat pembebanan, naiknya tekanan pori atau
ke-tidakstabilan lereng
• Bat klastik kasar, dicirikan oleh konfigurasi mounded atau bentuk sheet. IRC
A
B
Contoh
Rekaman seismik sedimen-klastik halus (A) & kasar. (B)
Batuan Karbonat
Endpn Paparan Karbonat buildup; Sisi belakang shelf margin ke arah utara td
atas perselingan lap batugamping & serpih, dgn IRC paralel, frekuensi tinggi &
amplitudo rendah, refleksi interval yg buruk. Ke arah cek di selatan td endp
kalkareous btr halus dgn down lap & variasi amplitudo lateral
• Refleksi pd bts atasnya menghasilkan RC (+)
• Pd kasus bat karbonat, sgt berpori, mk bts atas nya menghasilkan RC(-).
• amplitudo tinggi, kontinyuitas baik & bila cukup tebal akan mempunyai kecepatan interval yg tinggi (≥3500 m/s)
• ERC berbentuk sheet: penyebaran lateralnya sgt ekstensif & tdr atas
partikel karbonat berbtr hls atau fosil mikro karbonatan yg terendpkan dr
konfigurasi refleksi
diagnostik endpn
kar-bonat
Barrier
Shelf margin Pinnacle
Jenis build up
karbonat yg dpt
dikenali dr seismik
pl
at
fo
rm
Patch
Basement
Garam
Garam mempunyai ρ ± 2.2 gr/cc, < dibandingkan jenis sedimen lainnya. Bila
diendapkan dgn ketebalan yg cukup, mk akan tdk stabil, bila tertutupi oleh
bat lainnya dgn ρ >>mk akan terjadi aliran gararn dgn tahapan: pillowing,
diapirism, post diapirism & akan membentuk IRC yg unik
Batuan Dasar
‒ banyak multipel. terbentuk pola reflection free.
‒ Bat dasar ekonomik mempunyai Ф kecil akan dicerminkan oleh refleksi
lemah, diskontinyu akibat IA yg rendah & kwalitas data yg buruk
Batuan Beku & Volkanik
‒ Kecepatan interval tinggi, CR (+) & amplitudo yg tinggi
‒ Mempunyai bentuk eksternal & struktur internal yg sama dgn bat sedimen
Hidrokarbon
‒ Flat spot ini, mempunyai CR +, tampil sbg palung pd polaritas normal SEG
atau puncak pd polaritas terbalik
‒ Meskipun kontak gas ini selalu berbentuk datar pd penampang kedlman,
tapi pd penampang waktu bisa menunjukkan efek push-down akibat
kece-patan rendah dr gas ini.
Efek Diagenesa.
Efek diagenesa yg mengakibatkan perubahan harga densitas &
kecepat-an jelas akan mempengaruhi rekaman seismik & menimbullcan
potensi jebakan
Ekspresi
seismik
batuan
dasar
krisalin
a
Ekspresi seismik dr diapir
garam
Ekspresi seismik komplek volkanik
Di bawah reflek
si kuat dr batas
atas bat dasar
tsb (CR +),
re-kaman
seismik
menunjukkan
pola reflection
free
Geological Model Seismic Expression Geological Model
(normal polarity)
IIustrasi efek kehadiran gas pd IA reservoar
Ilustrasi anomali daerah
terang pd rekaman
seismik
Ilustrasi anomali
rekaman seismik
Seismic Expression
(normal polarity) No
reflection
Effect of different reservoir
pro-perties on the seismic
response to the presence of gas.
In the example, the reservoir is
overlain by relatively low-AI
sha-le. a) Reservoir of porous
sand with lower- AI than the
shale. b) Moderately porous
sand with slightly greater AI than
the shale. c) A porous limestone
or low∅ sandstone with greater
AI than the shale. d) A less
porous lime-stone with much
daerah
pd
higher AI buram
than the shale.
Dim spot associated with a gas-bearing porous
Bright spot in a shallow-gas sand carbo nate overlain by interbedded sands & shales.
Perubahan Litologi, Diagenesa, Kandungan
hidrokarbon
Efek perubahan batuan Sedimen mekanis
disimpulkan bhw:
• Refleksi seismik, dihasilkan dr batas atas & bawah unit lap &
cenderung mengikuti suatu kombinasi dr grs & rumpang waktu.
Bila terdpt struktur internal yg berskala signifikan (mis klinoform
skala besar), refleksi & bid atas maupun dasar akan mengikuti
ketidakselarasan.
• Refleksi mengikuti batas litologi tapi bukan batas fasies.
Peru-bahan lateral fasies umumnya akan dicerminkan oleh
peruba-han amplitudo, bentuk gel, frekuensi & kontinyuitas.
• Bila suatu unit klastik yg tebal membentuk kipas bawah laut dlm
lingk air dlm, refleksi dr bid permukaan atas & struktur internal
akan mengikuti rumpang waklu, sedangkan refleksi & batas
ba-wah interval turbidit klastik akan mengikuti grs waktu.
• Pd lingk klastik dangkal, unit individual sgt tipis shg terletak
an-tara ketebalan tuning & detectable limit. Oleh krnnya
perubahan ketebalan hanya akan mempengaruhi amplitudo
refleksi.
Kegunaan Data Seismik Refleksi
•
•
•
•
•
•
•
•
Mengetahui Gejala Deformasi Struktur Pasca
Pengendapan
Korelasi Waktu Geologi
Genesa Satuan Pengendapan
Ketebalan & Lingkungan Satuan Pengendapan
Paleobatimetri
Burial History
Relief & Topografi Bidang Ketidak Selarasan
Paleogeografi & Sejarah Geologi