CRS

1. Zero-Offset Common Reflection Surface
(ZO- CRS –Stack)
Bagian 4:
Contoh-contoh kasus

2. Synthetic example
Contoh-contoh kasus diambil dari Skripsi S1 dan Thesis
S2 ex-mahasiswa Prodi Teknik Geofisika ITB sbb:
1. Prias Dian Anggraini (2008)
2. Ekkal Dinanto (2009)

3. Vp=1524 m/s Rho=1.01 g/cc
Vp=1800 m/s Rho=2.5 g/cc
Vp=2200 m/s Rho=2.6g/cc
Vp=3700 m/s Rho=2.7 g/cc
Synthetic Case Study No. 1: Model subsurface yang berundulasi

4. Low Fold High Fold
Dominant frequency 15 Hz 15 Hz
No of live channel 120 120
Number of shot 10 500
Sampling rate 2 ms 2 ms
Depth of source (below sea
water surface)
30 m 30 m
Wavelet type Ricker Ricker
Type of source
Explosive
point source
Explosive
point source
Acquisition method Split Spread Split Spread
Near Offset 50 m 50 m
Record Length 4 s 4 s
Distance between receivers 25 m 25 m
Acquisition Parameter

5. Running the elastic and acoustic waveform modeling through the subsurface model
e.g. Acoustic waveform modeling with an explosive point source at X = 3000 m

6. Akustik Elastik comp Z Elastik comp X
Obtaining synthetic seismograms from the elastic waveform simulation

7. Fold coverage chart for low fold seismic data

8. Fold coverage chart for high fold seismic data

9. Low Fold
(10 shots)
High Fold
(500 shots)
Near surface velocity (survel) 1524 m/s 1524 m/s
VNMO (min, max) 1500- 4000 m/s 1500- 4000 m/s
Dip Reflector -60 , +60 -60 , +60
Aperture (min, max) 200, 4000 m 200, 4000 m
X midpoint aperture 350, 800 m 350, 800 m
Global coherence treshold 0.5 0.5
Rel coherence treshold 0.6 0.6
Coherence treshold (min, max) 0, 0 0, 0
Offset time (min, max) 0.3 -5.5 s 0.3 -5.5 s
Input data for the case study by using synthetic seismic data

10. Result obtained from
CRS-Stack method
Result obtained from
Conventional method
Results of seismic data processing for low fold seismic data

11. Results of seismic data processing for high fold seismic data
Result obtained from
Conventional method
Result obtained from
CRS-Stack method

12. Grid 4.5 m
Parameter Akuisisi : shot 160, channel 160, fold max 20, off end,
sampling int 4ms, int geophone 12.5m , fd 25 Hz
Synthetic Case Study No. 2: Model petroleum reservoir

13. Simulasi Akuisisi

14. Shot gather data sintetik

15. Penampang stack sintetik dari proses konvensional stack

16. Kategori Parameter CRS Nilai
Parameter umum
frekuensi dominan 25 Hz
ukuran koherensi Semblance
input koherensi Trace ternormalisasi
window koherensi 15
Kecepatan
v0 1500
rentang kecepatan stacking 1450 – 3600 m/s
Apertur dan taper
apertur ZO minimum 50 m pada 0 s
apertur ZO maksimum 500 m pada 4 s
apertur CMP minimum 12.5 m pada 0s
apertur CMP maksimum 2000 m pada 4 s
ukuran taper relative 0.3
Linier dan ZO
rentang α -600 s.d 600
pertambahan α 1
jumlah iterasi 3
Parameter CRS-stack

17. Penampang stack sintetik dari proses CRS-stack

18. CRS Supergather

19. Model kecepatan

20. Penampang Konvensional Stack

21. Penampang CRS-Stack

22. Penampang Partial-Stack CRS

23. Real Data examples
Contoh-contoh kasus diambil dari Skripsi S1 dan Thesis
S2 ex-mahasiswa Prodi Teknik Geofisika ITB sbb:
1. Prias Dian Anggraini (2008)
2. Andri Hendriyana (2009)
3. Ekkal Dinanto (2009)
4. Ariesty R. Asikin (2009)
dan hasil-hasil yang diperoleh dari WIT (Wave Inversion
Technology)

24. Real data example:
Low Fold Data taken from
PreTIGap marine survey mission,
Western Sumatra

25. The Raw Data: Shot Gather
The difficulties appear
then in
1. Velocity analysis
2. Multiple suppresion
Low S/N-ratio due to:
1. Coherence events are
identified only for water
bottom reflector.
2. After amplitude
correction by using
AGC, scaling, and
TAR, better
appearance of other
reflections that are
located below 2 s can
not be made yet.

26. Processing steps that have been applied up to this stage are:
1. Frequency filtering 6-12-40-50
2. Amplitude correction due to spherical divergence
3. NMO correction by using homogenenous velocity of 1500 m/s
4. Stacking.
Bubble effect
Brute Stack 1

27. Processing steps that have been applied up to this stage are:
1. Frequency filter 6-12-40-50
2. Amplitude correction due to spherical divergence
3. Debubble with predictive deconvolution (operator 120 ms and lag 8 ms)
4. NMO correction by using homogenenous velocity of 1500 m/s
5. Stacking
Brute Stack 2

28. Conventional CMP-stack section
Processing steps that have been applied up to this stage are:
1. Frequency filter 6-12-40-50
2. Amplitude correction due to spherical divergence
3. Debubble with predictive deconvolution (operator 120 ms and lag 8 ms)
4. NMO correction by using stacking velocity taken from velocity analysis
5. Stacking

29. Input parameter for ZO CRS-Stack

30. Conventional stack-Marine seismic data

31. CRS-stack-Marine seismic data
1. Higher S/N-ratio
2. Better image for dipping reflection events
3. Stronger diffraction

32. Aperture: 140-400
Aperture: 500-700

33. NIP
N
d
m
hw
R
R
f
v
x
x
F
1
1
2
cos
1 0
0




 Mann (2002)

34. Section of ratio between fresnel zone to aperture

35. Conventional
stack section
ZO CRS-stack
section

36. • The number of involved traces in determining ZO CRS-Stack operator is much higher than
the conventional one.
• ZO CRS-Stack attributes can be used for reflector characterization in more detail

37. Further Plan:
Development of Software

38. ITB – Pertamina EPTC Softwares
CRS Tomography
Pre Stack
Dept
Migration

39. Poster Software ASPS

40. 04 Leaflet Seismik luar

41. 04 Leaflet Seismik dalam