1. An introduction to CRS processing …

2. An introduction to CRS processing …
Presentation Outline
Introducing the methodology of CRS
CRS in time processing, case studies
CRS depth processing: CRS tomography and CRS PreSDM
CRS in reservoir description: Amplitude preservation, CRS AVO, fault
pattern enhancement

3. CRS Methodology
Subsurface Models (2D case)
NMO Model CRS Model
 location  location, dip, curvature
 1 Parameter :  3 Parameters:
vNMO RNIP , RN
2 2
2 2 4h 2 2 sin 2t0 cos 2 x2 h2
t h t 0 2
t t0 x
v NMO v0 v0 RN RNIP
with: Δx = midpoint distance ; h = half offset
Concept of model-independent imaging Hubral (1999)

4. CRS Methodology
RNIP R
N
NIP R
= =
Normal Reflector
Incidence Point segment
(Mann et al., 1999)
Point source at NIP: Exploding reflector R:
- Emergence angle a - Emergence angle a
- Wavefront curvature RNIP - Wavefront curvature RN

5. CRS Methodology
NMO/DMO CRS
(Hubral et al. 1999)

6. CRS Methodology
Stacking aperture is limited within
projected Fresnel zone
 preservation of lateral resolution
CRS

7. CRS Theory
CMP DMO versus CRS
DMO CRS
Time
Land data example
CRS stack improvement due to increased fold

8. CRS Theory
CMP DMO versus CRS
NMO CRS
Time
~10 ~100
~100 ~1000
Associated fold increase by CRS

9. CRS time domain processing Example 2
Std. 3D PostSTM CRS 3D PostSTM

10. CRS time domain processing Example 2
Std. 3D PostSTM CRS 3D PostSTM

11. CRS time domain processing
An existing 3D seismic dataset was used as basis for simulating
different acquisition geometries. The initial design was widely used
onshore Germany in the 1980s and 1990s
Distance of receiver lines 400 m
Receiver distance 50 m
Distance of shot lines 400 m
Shot distance 50 m
Spread 6 lines, 80 receiver each
Bin size 25 m x 25 m
Nominal fold 15

12. CRS time domain processing
E p ne
mägr
f
Receiver S Shots k
cusu t
hspn e
Asadesign e a Vrat 1 1
ugnsc m a n
Initial gsh i Subset
e Vrat 22
a Subset
in e Vrat 3 3
a Subset
in e
j dr2S
ee . P SP
Every other j Every S us alinee Every2S us ae e
ee . otherst v r
d 2 c shot e
h r s j d other shot liner
ee . c st v s
h r
Every2E p nei line
j d other receivern
ee . mägr i
f l e
Ü r ekfold1-ah
b dcug 5 c
e 15 n f Ü r ekfold8 ah
b dcug - c
e 8 n f Ü r ekfold8 ah
b dcug - c
e 8n f Ü r ekfold4 ah
b dcug - c
e 4 n f

13. CRS time domain processing
DMO (initial setup) CRS (initial setup)
500 ms
1000 ms
1500 ms
2000 ms
2500 ms
0 1 2 km
15 fold 15 fold

14. CRS time domain processing
DMO (initial setup) CRS (subset 3: every other SL&RL)
500 ms
1000 ms
1500 ms
2000 ms
2500 ms
0 1 2 km
15 fold 4 fold

15. CRS Gather
The natural extension of the CRS stack technology
is the development of CRS gathers.
CRS gather mark a major breakthrough:
 They allow for advanced prestack data analysis
 The improved data quality is transfered into
prestack migrated time/depth domain
 The newly developed acquisition geometry reconstruction
allows for using any type of prestack migration, e.g. RTM
 Data gaps within the range of the aperture can be filled
honouring the local dip/azimuth and curvature

16. CRS Methodology
Fit of stacking surfaces / reflection time surfaces
CRS partial stacking … around a certain central CMP/offset location
- where an input trace may exist or not
- where a CRS prestack trace is produced
as part of a CRS gather

17. Types of CRS Gather
Input CMP CRS offset CRS shot
gather regularization reconstruction
Different types of CRS gather calculation

18. Typical Problems in Land Data Acquisition
Original
Gathers
Regularized
CRS Gathers

19. CRS Gather
Shot sorted input data

20. CRS Gather
Acquisition geometry reconstructed CRS data

21. CRS Gather for 3D Prestack Time Migration
CMP Input
CRS Input

22. An introduction to CRS processing …
Presentation Outline
Company profile
Introducing the methodology of CRS, historical background
CRS in time processing, case studies
CRS depth processing: CRS tomography and CRS PreSDM
CRS in reservoir description: Amplitude preservation, CRS AVO, fault
pattern enhancement
Current CRS developments

23. CRS Tomography Introduction & Theory
RN
X0 RNIP
“relates” to reflector’s dip
RNIP “relates” to reflector’s depth
RN “relates” to reflector’s shape
(radius of curvature)
NIP

24. CRS Tomography Introduction & Theory
Original velocity model used for
calculation of synthetics
Reconstructed velocity model
after CRS processing on synthetics
and CRS tomography
Reconstructed velocity model with
ray tracing overlay
CRS tomography application to 2D synthetic data (Duveneck 2004)

25. CRS Tomography Introduction & Theory
(Duveneck 2004)
Reconstructed velocity model with overlay of horizon migrated
reflector elements (top).
Original velocity model with overlay of same migrated reflector
elements (bottom).

26. CRS Tomography 3D Case Study Mexico onshore
Salina del Istmo Basin

27. CRS Tomography 3D Case Study Mexico onshore
CMP Stack
Time [s]
Land seismic 400 sqkm
2.0
Acquisition Date: 1990s
Dynamite
2.5
Acquisition Fold: 30 nominal
3.0
Max Offset: 3800m in inline
3200m in crossline
3.5
4.0
Problems:
Low signal to noise ratio due to
4.5 irregular acquisition patterns
(permit problems)
5.0 Salt pillows influence data quality
5.5
Approach:
6.0 CRS Depth processing
4 km

28. CRS Tomography 3D Case Study Mexico onshore
CMP Stack CRS Stack
Time [s]
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
4 km

29. CRS Tomography 3D Case Study Mexico onshore
Dix model CRS tomography model
0
Velocity
[km/s]
1
4.4
2
4.0
Depth [km]
3 3.6
3.2
4
2.8
5
2.4
6 2.0
4 km

30. CRS Tomography 3D Case Study Mexico onshore
Interval Velocity [m/s] Depth [m]
2000 3000 4000 0 2000
0
200
Sonic Log
400
CRS Tomo
600
Time [ms]
800
1000
1200
1400

31. CRS Tomography 3D Case Study Mexico onshore
Tomography with Salt Body
Velocity
[m/s]

32. CRS PreSDM 3D Case Study Mexico onshore
0
1
2
3
4
Depth [km]
5
6
7
8
9
10
PreSDM CRS-PreSDM
PreSDM results: same migration algorithm, same velocity
model, standard gathers (left) vs. CRS input gathers (right)

33. Example 2: CRS Tomography in Overthrust Areas

34. CRS Tomography 3D Case Study Mexico onshore
• CRS tomography - a fast and efficient way to create a velocity-depth model
• Grid tomography on CRS attributes at selected locations only
(poststack process!)
• Works even on low fold data
• Resulting smooth velocity model is ideal for migrations
• Cuts down turn-around time in PreSDM dramatically

35. CRS gathers
Some types of CRS gathers … for depth migration
CRS offset regularized gathers Kirchhoff Prestack depth migration
CRS shot gathers WEM, RTM
with geometry preservation
CRS shot gathers RTM with regularized shots and
with geometry optimisation receiver patterns

36. CRS PreSDM – Golf of Mexico
RTM CMP
RTM on CMP gathers

37. CRS PreSDM – Golf of Mexico
RTM CRS
RTM on CRS shot gathers

38. CRS PreSDM – Land Data Example

39. An introduction to CRS processing …
Presentation Outline
Company profile
Introducing the methodology of CRS, historical background
CRS in time processing, case studies
CRS depth processing: CRS tomography and CRS PreSDM
CRS in reservoir description: Amplitude preservation, CRS AVO, fault
pattern enhancement
Conclusions

40. CRS Reservoir
Standard CMP gather across a filled gas storage

41. CRS Reservoir – Example 1
AVO effect
CRS gather, identical flow than standard gathers except for CRS

42. CRS Reservoir – Example 1
Standard AVO section across gas storage
CRS AVO section. Note red anomalies indicating the presence of gas

43. CRS Reservoir – Example 2
Shallow Gas Sands
Map View at Reservoir Depth
From conv. AVO Processing
Map View after CRS-AVO

44. Lateral Resolution – Time Slice
3D PreSTM 3D Migration of CRS

45. Thank you for your attention !