![Page 1: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/1.jpg)
Primaries and multiple: stack
![Page 2: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/2.jpg)
Stack
![Page 3: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/3.jpg)
Stack: 7% wrong velocity
![Page 4: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/4.jpg)
Zero-offset gather (no stacking)
![Page 5: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/5.jpg)
Effect velocity on stack/migration
![Page 6: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/6.jpg)
CMP sorting
shot data
image
NMO correction
(zero-offset) migration
stack
velocity model
velocity model
Processing flow
![Page 7: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/7.jpg)
Migration (zero-offset)
Stacked section is assumed to be zero-offset
(as if you shot with 1 geophone, and geophone at shot position)
A zero-offset section:
energy is still not focussed !!!
![Page 8: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/8.jpg)
Diffractor: zero-offset Modelling
(we know the Earth: Position of diffractor and seismic velocity)
![Page 9: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/9.jpg)
Diffractor: zero-offset
Migration (we do NOT know
the position of diffractor, but do
know the velocity)
![Page 10: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/10.jpg)
Diffractor: zero-offset
Migration (we do NOT know
the position of diffractor, but do
know the velocity)
![Page 11: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/11.jpg)
Diffractor: zero-offset stack
![Page 12: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/12.jpg)
Diffractor: zero-offset stack
(60-fold stack)
![Page 13: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/13.jpg)
Migration on dipping reflector Modelling
(we know the Earth: Position of reflector and seismic velocity)
![Page 14: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/14.jpg)
Migration on dipping reflector
Migration (we do NOT know
position of reflector, but do know
seismic velocity)
![Page 15: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/15.jpg)
Migration on piece of dipping reflector:
- Moves piece up-dip
- Makes dip steeper
- Makes piece shorter
![Page 16: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/16.jpg)
Migration (we do NOT know
position of reflectors and diffractors, but do know
seismic velocity)
Migration on dipping reflector
![Page 17: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/17.jpg)
Apparent dips
Zero-offset section:
(depth-) migrated section = depth section:
(time-) migrated section:
![Page 18: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/18.jpg)
Dip
T = 2 R/c = 2 √(x2+z2)/c ∂T/∂x = (2/c) ½ (x2+z2)-½ 2 x = (2/c) x/(x2+z2)½
= (2/c) x/R sin θ = x/R So: ∂T/∂x = 2/c sin θ
θ
R
x
z
![Page 19: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/19.jpg)
Double-dip
Zero-offset section: before migration
After migration
![Page 20: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/20.jpg)
Double-dip (2)
Migration with too low velocity
Migration with too high velocity
![Page 21: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/21.jpg)
Syncline
![Page 22: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/22.jpg)
Syncline model with
ray paths
![Page 23: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/23.jpg)
Syncline: real data example
![Page 24: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/24.jpg)
Migration:
HOW ??
![Page 25: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/25.jpg)
1 Diffractor: zero-offset
“Wiggle plot”: Signals next to each other
![Page 26: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/26.jpg)
1 diffractor: zero-offset
“Image plot”: Like a photograph
![Page 27: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/27.jpg)
1 diffractor: zero-offset
Migration: Add along hyperbola
(we do know velocity)
![Page 28: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/28.jpg)
4 diffractors: zero-offset
![Page 29: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/29.jpg)
4 diffractors: zero-offset
![Page 30: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/30.jpg)
8 diffractors: zero-offset
![Page 31: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/31.jpg)
16 diffractors: zero-offset
![Page 32: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/32.jpg)
32 diffractors: zero-offset
![Page 33: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/33.jpg)
Exploding-reflector model
Zero-offset response can be simulated by putting sources at reflector and take half the medium velocity
![Page 34: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/34.jpg)
9 diffractors: zero-offset
![Page 35: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/35.jpg)
17 diffractors: zero-offset
![Page 36: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/36.jpg)
33 diffractors: zero-offset
![Page 37: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/37.jpg)
49 diffractors: zero-offset
![Page 38: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/38.jpg)
Processing
Input: Multi-offset shot records Results of processing (after migration):
1. Structural map of impedance contrasts
2. Velocity model
![Page 39: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/39.jpg)
Effect migration
![Page 40: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/40.jpg)
Conversion from time to depth
Migration examples so far: output section in time
This is called time migration Still, data needs to be converted to depth: true earth Simplest case: horizontal layers From root-mean-square velocities to interval velocities:
Dix’ formula
![Page 41: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/41.jpg)
Dix’ formula: from VRMS to VINTERVAL
(pdf-eqs)
![Page 42: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/42.jpg)
Conversion from time to depth via Dix’ formula
Theoretically: valid for plane horizontal layers (Theoretically: no migration necessary)
Practically: still works well for dipping reflectors and mild
lateral velocity variations, but then: AFTER (time) migration
![Page 43: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/43.jpg)
CMP sorting
shot data
image
NMO correction
(zero-offset) migration
stack
velocity model
velocity model
Processing flow
![Page 44: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/44.jpg)
Strategy for seismic migration
Why ? In beginning: only RMS-velocity model known: very crude
à time migration (relatively fast/cheap) When one well available: better (interval-) velocity model
à some depth migration possible (relatively slow/expensive) When more wells available: good (interval-) velocity model known
à pre-stack depth migration possible (slow/expensive !$!)
![Page 45: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/45.jpg)
Strategy for seismic migration
• Simple structure: post-stack migration • Complex structure: pre-stack migration
(such as DMO)
• Small lateral velocity variations: time migration • Large lateral velocity variations: depth migration
(no hyperbolae any more)
![Page 46: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/46.jpg)
Complex structure: simplest case of diffractors
depth
![Page 47: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/47.jpg)
Complex structure: simplest case of diffractors
Stack with no DMO
![Page 48: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/48.jpg)
Complex structure: simplest case of diffractors
Migrated stack With no DMO
![Page 49: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/49.jpg)
Complex structure: simplest case of diffractors
Stack with DMO
![Page 50: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/50.jpg)
Complex structure: simplest case of diffractors
Migrated stack With DMO
![Page 51: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/51.jpg)
Complex structure: simplest case of diffractors
Complex case: DMO = form of pre-stack time migration necessary
(only root-mean-square-velocity model necessary)
![Page 52: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/52.jpg)
Large lateral velocity variations: time section
![Page 53: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/53.jpg)
Large lateral velocity variations: depth section
![Page 54: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/54.jpg)
Large lateral velocity variations
Notice lateral shift of faults as well (so here time-stretching axis will not do !!!)
![Page 55: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/55.jpg)
Kirchhoff Pre-stack Time Migration
![Page 56: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/56.jpg)
Kirchhoff Pre-stack Depth Migration
![Page 57: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/57.jpg)
Kirchhoff Pre-stack Time Migration
![Page 58: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/58.jpg)
Wave Equation PSDM
![Page 59: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/59.jpg)
Large lateral velocity variations and complex structure
![Page 60: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/60.jpg)
Large lateral velocity variations and complex structure
(Interval-) velocity model
![Page 61: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/61.jpg)
Velocities/Structures and migration
![Page 62: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/62.jpg)
Strategy for seismic migration
• Simple structure, small lateral velocity variations: post-stack time migration
• Complex structure, small lateral velocity variations:
pre-stack time migration (generalisation DMO)
• Simple structure, large lateral velocity variations: post-stack depth migration (pull-up effect)
• Complex structure, large lateral velocity variations :
pre-stack depth migration (e.g. side of salt domes)
![Page 63: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/63.jpg)
Migration: wave theory
Migration is:
( X , Y , T ) à ( X , Y , Z )
or, better,
( X , Y , Z=0 , T ) à ( X , Y , Z , T=0 )
![Page 64: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/64.jpg)
Migration: wave theory
Transform measurements at z=0 for all t into measurements for t=0 for all z !
Two-step procedure:
1: Extrapolation:
Bring P ( x , y , z=0 , t ) to P ( x , y , z=zm , t )
2: Imaging = Select only t=0: Pmigr ( x , y , z=zm , t ) = P ( x , y , z=zm , t=0 )
![Page 65: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/65.jpg)
Wavefield extrapolation
![Page 66: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/66.jpg)
Wavefield extrapolation
![Page 67: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/67.jpg)
Wavefield extrapolation (2)
![Page 68: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/68.jpg)
Zero-offset migration scheme
Zero-offset migration can be applied by: • Consider zero-offset data as exploding reflector measurements in medium with half the true velocity • Extrapolating surface data into subsurface
• At t=0, the imaged reflector should appear at correct depth ( Imaging condition )
Often for geological interpretation, the output is calculated as a function of time.
![Page 69: Presentation Chapter 5: Processing of Seismic Reflection Data (Part 2)](https://reader033.vdocument.in/reader033/viewer/2022061206/5481c6cbb4af9f0b318b462d/html5/thumbnails/69.jpg)
Ideal migration when velocity model is known
• Inverse wavefield extrapolation receivers into medium
• Forward wavefield extrapolation source into medium
• Correlate two resulting wavefield
• Extract t=0 component
Pre-stack Depth Migration: