seismic migration
TRANSCRIPT
![Page 1: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/1.jpg)
Seismic Migration (SM)
Januka AttanayakeGEOL 377
Center for Integrative GeosciencesUniversity of Connecticut
13th November 2006
![Page 2: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/2.jpg)
Goals:
1) What is SM?
2) Why is it used?
3) How is it used?
![Page 3: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/3.jpg)
3
Couple of things
Feel free to take notesReferences are given when ever possible4 Simple in-class questionsHome work assignment, e-mailed to youMigration:
-concept, easy to understand-application in algorithms, TERRIBLE !!
![Page 4: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/4.jpg)
4
Content
Background information-Refraction survey-Reflection survey
Seismic Migration-Principles, Fundamental concepts-Hand Migration-Different Approaches-Different techniques based on sequence
![Page 5: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/5.jpg)
Seismic WavesStretch, squeeze & Shear material(Earth Material = Sponge)
Stress & Strain:
Equation of Motion:
ijijij eµλθδσ 2+=
Modern Global Seismology, P. 49-51
uuu ×∇×∇−⋅∇∇+= µµλρ )()2(
Modern Global Seismology, P. 53-69
![Page 6: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/6.jpg)
Motion of particles
![Page 7: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/7.jpg)
Snell’s Law
Willebrord van Roijen Snell(1580-1626)
)sin()sin( rnin ri =
University Physics p.644-646
![Page 8: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/8.jpg)
Question - 1Do question number 1 in the in-class exercise sheet.
![Page 9: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/9.jpg)
Snell’s Law & Seismic waves
![Page 10: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/10.jpg)
Some energy loss
![Page 11: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/11.jpg)
Fundamental Observable
TRAVEL TIME
Our trusted friend !!
![Page 12: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/12.jpg)
Do question 2 in the in-class exercise sheet
V2>V1
![Page 13: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/13.jpg)
Time Relationships
1/VXTdir =
])/[cos(2 1VhTrefl θ=
12 /)cos(2)/( VhVXT crefr θ+=
![Page 14: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/14.jpg)
In a graph
![Page 15: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/15.jpg)
![Page 16: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/16.jpg)
Graphical representation-I
![Page 17: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/17.jpg)
Deep Earth Pseudo-analogy
Steven Dutch
PKP(AB,BC) direct waves
PKiKP Reflected wave
PKP(diff) Headwave
![Page 18: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/18.jpg)
Complexities
*Travel times (Velocity perturbations) *Ray paths are affected by the subsurface structures
*Noise
ρµ)34( += KVp
ρµ
=sV
![Page 19: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/19.jpg)
Enviroscan, inc.
![Page 20: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/20.jpg)
![Page 21: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/21.jpg)
Seismic MigrationMigration – Moving from one place to
another
What is Seismic Migration?“A data processing technique”
-Reflection seismic surveys-Accurate imaging of earth structures
Coming Attraction! “Proper Definition”
![Page 22: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/22.jpg)
SM History1921 – First use, at the beginning of Seismic
Exploration (seismic exploration,p.6, fig-1.3b)
1920/40 – “Human computer” based methods1960/70 - Emergence of digital wave
equation technique
Oil industry – 1970/90 and present
![Page 23: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/23.jpg)
23
Key Contributors
Principle ones: (Theoretical)F. Reiber, J.G. Hagedoorn, J.F. Claerbout
Others:C.H. Dix, M.M. Slotnick, H. Slattlegger, A.J. Berkhout, B Shneider, R. Stolt, Moore
Bednar J.B.
![Page 24: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/24.jpg)
Seismic reflection survey
1) Source
2) Detectors
3) Data processing system
![Page 25: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/25.jpg)
Source
![Page 26: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/26.jpg)
Detectors (Geophones)
![Page 27: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/27.jpg)
Data processing system
+ Seismologists
![Page 28: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/28.jpg)
Method
![Page 29: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/29.jpg)
Cross section
http://www.litho.ucalgary.ca/atlas/seismic.html
![Page 30: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/30.jpg)
Data Processing Sequence
http://www.litho.ucalgary.ca/atlas/seismic.html
![Page 31: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/31.jpg)
Final Picture
UNR – CEMAT
![Page 32: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/32.jpg)
Got a problem?
Each CDP stacked trace in a seismic section is plotted to show reflections in positions that correspond to vertical travel paths
CDP – Common Depth Point
![Page 33: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/33.jpg)
Zero-offset
Coincident source-receiver.
i.e. Location of the source is as same as the receiver.
Is this it?
Answer is ……..
![Page 34: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/34.jpg)
Inclined flat reflector problem
Basic Exploration p.188
![Page 35: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/35.jpg)
Undulating reflector problem
![Page 36: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/36.jpg)
Cause of distortionPlotting depths calculated from arrival times
in incorrect positions
*Not from incorrect travel times
![Page 37: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/37.jpg)
Seismic Migration
Dip distortion Correction by moving reflection points away from their positions on vertical lines on to inclined lines that correspond to the travel paths.
Process of placing seismic reflection energy in its proper subsurface location.
![Page 38: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/38.jpg)
Proper definitionSeismic migration involves the geometric repositioning of the return signals to show an event where it is being hit by the seismic wave rather than where it is picked up.
Event – Boundary (layer), Structure
M.Lorentz, R. Bradley
![Page 39: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/39.jpg)
39
BREAK
I am tired ! Lets have a 10 minute BREAK !!
![Page 40: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/40.jpg)
Basic Idea
![Page 41: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/41.jpg)
Question -3Do question 3 (a),(b) of in-class exercise
sheet.
![Page 42: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/42.jpg)
42
Answer
![Page 43: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/43.jpg)
Finding dip angle
![Page 44: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/44.jpg)
44
Question -4
Do question 4 in your in-class work sheet.
![Page 45: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/45.jpg)
Migrator’s Equation
)V(
)(
)('
1
1
1
xtarcSin
xtVSin
tVzSinTan
∆∆
=
∆∆
=
∆=∆=
α
α
αβ
![Page 46: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/46.jpg)
True Coordinates
![Page 47: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/47.jpg)
2-way travel time w.r.t. normal ray length
Vdt 2
=
True depth of reflector at point R
θdCosz =Lateral shift of true position
θθ SinVtdSinx2
==∆
It is conventional to write t in terms of 2-way vertical travel time t’
θtCosVzt ==
2'
Thus both vertical shift t-t’ and the horizontal shift ∆x = 0 (when dip angle =0)
Basic Earth Imaging- Claerbout
![Page 48: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/48.jpg)
Hand Migration(HM)Before computerized migrationSeveral schemes
∆x & t’ require,t – readily measured v – from finite-offset θ - measurable as follows…..
![Page 49: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/49.jpg)
ytp
∂∂
=0
Where; p0 - time dip of the event or simply dip of the event
y - The midpoint coordinate, the location of source-receiver pair
41'
4
2
22
2
0
pVtt
ptVx
VpSin
−=
=∆
=θTuchel’s Law;
![Page 50: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/50.jpg)
HM ProblemsEquations not practical
-tedious -error-prone
Why? Calculating/Inputting “P” problematice.g. crossing events – 2 reflectors but
same arrival timesSummation of such a wavefield
![Page 51: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/51.jpg)
What are these?
![Page 52: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/52.jpg)
Diffraction & Distortion
![Page 53: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/53.jpg)
True Point
![Page 54: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/54.jpg)
Purpose of Migration
1) Reposition reflections
2) Remove diffraction images
* General purpose migration
![Page 55: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/55.jpg)
True Picture
![Page 56: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/56.jpg)
Different Approaches
Time Reverse MigrationKirchhoff Migration
*In addition, there are many other approaches. (Exploration seismology p. 326-335)
![Page 57: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/57.jpg)
Time Reverse Migration“Depropagate” seismic waves to its origin. i.e. reverse the path of seismic reflections
back to the geologic reflector by reversing time
Literature: Hermon(1978), Baysal et.al.(1983), Loewenthal & Mufti(1983), McMechan(1983), Whitemore(1983,1986), Mufti et.al.(1996), Zhu & Lines (1998)
![Page 58: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/58.jpg)
Principle-IWe live in 4-D (space & time)
Any one of them can be reversed !Time, not physically!
why?
![Page 59: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/59.jpg)
Principle-IIWave Equation (1-D homogeneous medium)
Solution (D’Alembert)
f,g – twice differentiable arbitrary functions, holds true even if you substitute (-t)
2
22
2
2
zV
t ∂∂
=∂∂ ϕϕ
)()(),( zVtgzVtftzs ++−=
![Page 60: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/60.jpg)
Experiment, Hello olleH !• Time-Reversed Acoustics; November 1999; Scientific American
Magazine; by Fink; 7 Page(s) • In a room inside the Waves and Acoustics Laboratory in Paris is an
array of microphones and loudspeakers. If you stand in front of this array and speak into it, anything you say comes back at you, butplayed in reverse. Your "hello" echoes-almost instantaneously-as "olleh." At first this may seem as ordinary as playing a tape backward, but there is a twist: the sound is projected back exactly toward its source. Instead of spreading throughout the room fromthe loudspeakers, the sound of the "olleh" converges onto your mouth, almost as if time itself had been reversed. Indeed, the process is known as time-reversed acoustics, and the array in front of you is acting as a "time-reversal mirror."
![Page 61: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/61.jpg)
Example - Model
Fault bend fold
Fault propagation fold
Lines et.al. (2001)
![Page 62: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/62.jpg)
Example - Interpretation
Zero-offset sectionMigrated section
![Page 63: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/63.jpg)
Kirchhoff (diffraction-stack) Migration
Concept : Hagedoorn (1954)Curve of maximum convexity (PMR)i.e. unmigrated diffraction curve
![Page 64: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/64.jpg)
Kirchhoff Method#1 Calculate the diffraction curves for
each reflector point on the unmigratedsection
#2 Data on the unmigrated section lying along this curve summed up
#3 This gives the amplitude at the respective migrated point
If, Signal – approprate value Noise – (+) + (-) values (small sum)
![Page 65: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/65.jpg)
Kirchhoff MethodEach element of an unmigrated reflection is treated as a portion of a diffraction.
i.e. Reflector – sequence of closely spaced diffracting points
![Page 66: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/66.jpg)
Point Reflector
Diffraction migrates into a point
Diffraction curve of
an unmigrated
reflector element
![Page 67: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/67.jpg)
Array Reflector
![Page 68: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/68.jpg)
Linear Reflector
![Page 69: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/69.jpg)
NoiseBurst of noise in an unmigratedsection
Migrates in to a wavefront
“A Smile”
![Page 70: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/70.jpg)
NoteResults of wavefront smearing (previous
figures) are identical to Kirchhoff migration results (Sheriff, 1978).
![Page 71: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/71.jpg)
More notes…Amplitudes are adjusted for obliquity and
divergence before summing
Introduce a wavelet-shaping factor to correct amplitudes
(Schneider, 1979), (Berryhill, 1979)
Near-field terms are neglected for collapsing diffraction curves as wave propagation in spherical coordinates
![Page 72: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/72.jpg)
Aperture Definition ProblemAperture: Range of data included in the
migration of each point
How far down the diffraction curve the summation should extend?
General Rule:Aperture > 2x horizontal distance of width migration of the reflector having
steepest dips
![Page 73: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/73.jpg)
Other Kirchhoff approaches
Kirchhoff integral:Find integral Solution to the wave equation (Schneider 1978)
![Page 74: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/74.jpg)
Migration
Pre-Stack Migration
Post-Stack Migration
![Page 75: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/75.jpg)
Pre-stack Migration
Migrate data before stacking sequence occurs.
*Pre-stack depth migration (PDM)*Require more knowledge about subsurface
velocity structure*Better results
![Page 76: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/76.jpg)
Applications & Problems
# Complex subsurface structure
# Complex subsurface Velocity Structure
# Modeling salt diapirs
# Expensive
# Time consuming
![Page 77: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/77.jpg)
Pre-stack final picture
![Page 78: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/78.jpg)
Post-stack MigrationSeismic data is migrated after stacking sequence occurs.
Basis: All data elements-Primary Reflections-Diffractions
![Page 79: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/79.jpg)
Applications/Problems# Low dip non-interfering events
# Faster data processing
# Low cost
# Resolution < pre-stack migration
![Page 80: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/80.jpg)
Post-stack final Picture
![Page 81: Seismic Migration](https://reader033.vdocument.in/reader033/viewer/2022052303/547c09645906b595798b46b5/html5/thumbnails/81.jpg)
Main References:*Basic Exploration Seismology, Robinson & Coruh*Modern Global Seismology, Lay & Wallace*Exploration Seismology, Sheriff & Geldart*http://sepwww.stanford.edu/sep/prof/index.html* Lines et.al.(2001), Depth Imaging “if we could turn back
time”, CSEG Recorder *http://www.geol.lsu.edu/Faculty/Juan/ReflectSeismol97/rc
bradley/WWW/rcbradley1.html*Bednar.,J.B.(2005), A brief history of seismic migration,
SEG digital library, doi:10.1190/1.1926579*University Physics, Sanny & Moebs