Making CMP

1
Making CMPs
From chapter 16 Elements of 3D Seismology by
Chris Liner
2
Outline

• Normal Moveout
• Stacking

3
Normal Moveout
Hyperbola
x
T
4
Normal Moveout
x
T
Overcorrected
Normal Moveout is too large
Chosen velocity for NMO is too (a) large (b)
small
5
Normal Moveout
x
T
Overcorrected
Normal Moveout is too large
Chosen velocity for NMO is too (a) large (b)
small
6
Normal Moveout
x
T
Under corrected
Normal Moveout is too small
Chosen velocity for NMO is (a) too large (b) too
small
7
Normal Moveout
x
T
Under corrected
Normal Moveout is too small
Chosen velocity for NMO is (a) too large (b) too
small
8
Vinterval from Vrms
Dix, 1955
9
Vrms
V1
V2
Vrms lt Vinterval
V3
10
Vinterval from Vrms
11
Primary seismic events
x
T
12
Primary seismic events
x
T
13
Primary seismic events
x
T
14
Primary seismic events
x
T
15
Multiples and Primaries
x
M1
T
M2
16
Conventional NMO before stacking
x
M1
NMO correction VV(depth) e.g., Vmz B
T
M2
Properly corrected
Normal Moveout is just right
Chosen velocity for NMO is correct
17
Over-correction (e.g. 80 Vnmo)
x
x
M1
M1
NMO correction VV(depth) e.g., V0.8(mz B)
T
T
M2
M2
18
f-k filtering before stacking (Ryu)
x
x
M1
NMO correction VV(depth) e.g., V0.8(mz B)
T
T
M2
M2
19
Correct back to 100 NMO
x
x
M1
M1
NMO correction VV(depth) e.g., V(mz B)
T
T
M2
M2
20
Outline

• Convolution and Deconvolution
• Normal Moveout
• Stacking

21
NMO stretching
T0
V1
V2
NMO Stretching
22
NMO stretching
V1
T0
V2
NMO Stretching
V1ltV2
23
NMO stretching
V1
V1ltV2
NMO stretch linear strain
V2
Linear strain () final length-original length
original length
X 100 ()
24
NMO stretching
original length
final length
V1
V1ltV2
V2
X 100 ()
NMO stretch
X 100 ()
25
stretching for T2s,V1V21500 m/s
Green line assumes V1V2
Blue line is for general case, where V1, V2 can
be different and delT00.1s (this case V1V2)
Matlab code
X 100 ()
26
Stacking



27
Stacking improves S/N ratio



28
Semblance Analysis
X



Twtt (s)
Semblance
29
Semblance Analysis
X
V



V1
V2
Twtt (s)
V3
Peak energy