1. Noppadol Poomvises Geologist 6
Removing seafloor multiple using predictive deconvolution and NMO correction
Noppadol Poomvises
Geologist 6

2. Seismic suffering from undesirable noises.
Air
Water
0.013 s
Seafloor
SB =Primary reflection
from seafloor
M1=Twice-bounced
multiple
M2=Three-bounced R -R 2 4 3
R=-1 P M1 M2 M3
(a) Seafloor multiple model
(modified from Russel, 1993).
(b) Ghost model
(modified from Jadell, 1987).
Seafloor multiple
Seismic energy trapped between two strong interfaces of high reflection coefficient (R).
Periodicity interval equals to 2-way travel time.
Effect as wave-train reverberation in seismic stacked section.
Ghost
A short-path seismic pulse leaving source in upward direction, following and arriving at receivers closely with primary (P) signal.
Superimposition to primary and broadening seismic waveform.

3. Objectives of the study
To evaluate the ability of multiple attenuation, both in modeled and real data, using conventional predictive deconvolution (PDC) in common shot domain using Focus/Disco 4.1, the in-house processing software
To examine the multiple removing technique by applying the periodicity enhancement and PDC in the common shot domain, using the same software.
To compare the quality of processed data using the methods in 1 with those obtained from 2 to demonstrate whether significant improvement is achieved by the proposed technique.

4. Data collection Modeled data Real data
Generating modeled data on a two-layered and a three-layered models using a Forward modeling technique.
Using Osiris modeling s/w, Odegaard & Danneskoild-Samsoe, Denmark.
Running on a Unix-based computer, Sun Sparc 20, 128 MB RAM, and 20 GB hard disk.
Real data
Two real seismic data sets acquired on shallow seafloor of two different areas and times.
The Ist set contains fair degree of multiples while the 2nd set shows stronger degree of multiples.

5. Concept of the removing technique.

6. Data processing works. Generating modeled data. Verifying the data.
Processing modeled data.
Processing real data.

7. Generating modeled data.
Distance (m) 10
600
Distance (m)
Water surface 10
Water surface
600
1. Introducing earth models
and parameters to the S/W.
2. Simulating the models.
3. Receiving model shots. 10
Receiver array
Source
Receiver array 10
Source
Water layer
Depth (m)
Layer 1
V1 = 1,441 m/s, D = 1.0 kg/m3
100
Vw = 1,500 m/s, Dw = 1.0 kg/m3
Sea bottom 50
V2 = 1,800 m/s, D = 1.5 kg/m3
Layer 2
Vsb = 2,000 m/s, Dsb = 2.0 kg/m3
400
V3 = 5,250 m/s, D = 2.6 kg/m3
Layer 3

8. Generating the modeled and calculated shots
Distance (m) 10
Water surface
600
Source
Receiver array 10
Water layer
Depth (m)
Vw = 1,500 m/s, Dw = 1.0 kg/m3 50
Vsb = 2,000 m/s, Dsb = 2.0 kg/m3
Sea bottom
(a) A two-layer model for numerical computation
(a) A two-layer model for numerical computation
(c) Possibilities of seismic events predicted from the two-layer input model.
(d) A calculated shot computed from the two-layer input model.

9. Data verification by comparison between the modeled and calculated shot of the two-layer case.
Both contains primary and multiple events.
Well agreement between the simulated and predicted seismic events.

10. Data verification by comparison between the modeled and calculated shot of the three-layer case.
Both contains primary and multiple events.
Well agreement between the simulated and predicted seismic events.

11. Flow processing sequences of modeled data in three cases.
PDC
(2)
(3)

12. Processing results of two-layer modeled data
Figure 4 Processing result of two-layer model shots in three different cases
with their autocorrelation(middle), and semblance analysis (lower).
(a) No PDC
(b) Conventional PDC
(c) Periodicity before PDC
Changes

13. Processing results of three-layer modeled data
Figure 5 Processing result of three-layer model shots in three cases
with their autocorrelation(middle), and semblance analysis (lower).
(a) No PDC
(b) Conventional PDC
(c) Periodicity
before PDC
Changes

14. Processing sequence of real data and parameters used.
(The numbers in embraces are of the data set 2)

15. Processing results of 2-D seismic data set 1
Figure 6 Processing result in a shot record of real data set 1 in three different cases (above)
with their semblance analysis(below).
No PDC
Conventional PDC
Periodicity before PDC
Processing results of 2-D seismic data set 1
Changes

16. Normal stacked (NSTK) section with NO predictive deconvolution(PDC) of data set 1.
Figure 7 Normal stacked (NSTK) section of data set 1 with no predictive deconvolution (left) and its corresponding autocorrelation (right)
The numbers labeled are used to with other cases.

17. NSTK section with conventional PDC of data set 1.
Figure 8 Normal stacked (NSTK) section of data set 1 with conventional predictive deconvolution (left)
and its corresponding autocorrelation (right).

18. NSTK section with periodicity enhancement and PDC of data set 1.
Figure 9 Normal stacked (NSTK) section of data set 1 with periodicity before predictive deconvolution (left)
and its corresponding autocorrelation (right).

19. NSTK of data set 1 in three cases
NSTK with NO PDC
NSTK with conv. PDC
NSTK with periodicity enhancement and PDC

20. Autocorrelations of real data set 1 in three cases.
NSTK with No PDC
NSTK with PDC
NSTK with periodicity enhancement and PDC

21. Processing results of 2-D seismic data set 2
No PDC
Conventional PDC
Periodicity before PDC
Processing results of 2-D seismic data set 2
Changes
Figure Processing result in a shot record of real data set 2 in three different cases (above)
with their semblance analysis (below).

22. Normal stacked (NSTK) section with NO predictive deconvolution(PDC) of data set 2.
Figure 11 Normal stacked (NSTK) section of data set 2 with no predictive deconvolution (left) and its corresponding
autocorrelation (right). The numbers labeled are used to compared with other cases.

23. NSTK section with conventional PDC of data set 2.
Figure 12 Normal stacked (NSTK) section of data set 2 with conventional predictive deconvolution (left)
and its corresponding autocorrelation (right).

24. NSTK section with periodicity enhancement and PDC of data set 2.
Figure 13 Normal stacked (NSTK) section of data set 2 with periodicity before predictive deconvolution (left)
and its corresponding autocorrelation (right).

25. NSTK of data set 2 in three cases
NSTK with NO PDC
NSTK with conv. PDC
NSTK with periodicity enhancement and PDC

26. Autocorrelation of data set 2 in three cases.
NSTK with PDC
NSTK with periodicity enhancement and PDC
NSTK with NO PDC

27. Conclusions
1. Conventional PDC in common shot domain can suppress some amount of seafloor multiples from seismic data, especially at near offset range.
2. Periodicity enhancement and PDC can remove much amount of seafloor multiples from both data, especially at middle- and far-offset range.
3. The new technique can comparatively removes the seafloor multiples from seismic data much amount than that of the conventional technique.
4. Performance of the new technique relatively gives better improvement of the quality, and enhances resolution of stacked section than of the conventional method as well.

28. Recommendations
The package of NMO/PDC/DNMO consumes only a few CPU time than of the conventional one, therefore it is attractive to apply the method in an actual data processing work.
For better development of seafloor multiple removing technique, it is of interested to further study the effectiveness of this method in future by compiling the package in common shot domain with other existing removing techniques.

29. Acknowledgements. Dr.Chalermkiet Tongtaow Dr.Banjob Yodsombat
PTTEP public Co., Ltd.
Providing an excellence chance.
Supporting hardware, software, and valuable seismic data used.
CMU
The place I really love and memorize.
The place that giving so many things more than education.
Dr.Chalermkiet Tongtaow
Dr.Banjob Yodsombat
Dr.Pisanu Wongpornchai
Dr.Somchai Sri-israporn
Mr.Montri Rawanchaikul
Mr.Booncherd Kongwang
For their advise, guidance, and unwavering standing by me during my time of researching.

30. Million thanks !
For the good time
on the Loy Krathong festival !!