making cmp’s
DESCRIPTION
Making CMP’s. From chapter 16 “Elements of 3D Seismology” by Chris Liner. Outline. Normal Moveout Stacking. Normal Moveout. Hyperbola:. x. T. Normal Moveout. x. T. “Overcorrected”. Normal Moveout is too large. Chosen velocity for NMO is too (a) large (b) small. Normal Moveout. - PowerPoint PPT PresentationTRANSCRIPT
Making CMP’s
From chapter 16 “Elements of 3D Seismology” by Chris Liner
Outline
•Normal Moveout
•Stacking
Normal Moveout
22 2
0 2
xT T
V
22
0 0 02( ) ( )
xT x T x T T T
V
x
T
Hyperbola:
Normal Moveoutx
T
“Overcorrected”
Normal Moveout is too large
Chosen velocity for NMO is too
(a) large (b) small
Normal Moveoutx
T
“Overcorrected”
Normal Moveout is too large
Chosen velocity for NMO is too
(a) large (b) smallsmall
Normal Moveoutx
T
“Under corrected”
Normal Moveout is too small
Chosen velocity for NMO is
(a) too large
(b) too small
Normal Moveoutx
T
“Under corrected”Normal Moveout is too small
Chosen velocity for NMO is
(a) too largetoo large
(b) too small
Vinterval from Vrms
122 2
1 1interval
1
n n n n
n n
V t V tV
t t
Dix, 1955
2i i
RMSi
V tV
t
Vrms
V1
V2
V3
Vrms < Vinterval
Vinterval from Vrms
Vrms T Vinterval from Vrms ViViT VRMS from V interval1500 0 01500 0.2 1500 450000 15002000 1 2106.537443 4000000 20003000 2 3741.657387 18000000 3000
SUM 3.2 22450000
Primary seismic eventsx
T
x
T
Primary seismic events
x
T
Primary seismic events
x
T
Primary seismic events
Multiples and Primariesx
TM1
M2
Conventional NMO before stackingx
TNMO correction
V=V(depth)
e.g., V=mz + B
M1
M2
“Properly corrected”
Normal Moveout is just right Chosen velocity for NMO is correct
Over-correction (e.g. 80% Vnmo)
x
TNMO correction
V=V(depth)
e.g., V=0.8(mz + B)
M1
M2
x
TM1
M2
f-k filtering before stacking (Ryu)
x
TNMO correction
V=V(depth)
e.g., V=0.8(mz + B)
M1
M2
x
T
M2
Correct back to 100% NMO
x
TNMO correction
V=V(depth)
e.g., V=(mz + B)
M1
M2
x
TM1
M2
Outline
•Convolution and Deconvolution
•Normal Moveout
•Stacking
NMO stretching
V1
V2
T0
“NMO Stretching”
NMO stretching
V1
V2
T0
“NMO Stretching”
V1<V2
NMO stretching
V1
V2
V1<V2
0 0T T0T 1T
1 1T TNMO “stretch” = “linear strain”
Linear strain (%) = final length-original length
original length
X 100 (%)
NMO stretching
V1
V2
V1<V2
0 0T T0T 1T
1 1T T
X 100 (%)
original length = 1T final length = 0T
NMO “stretch” = 0 1
1
T TT
X 100 (%)0
1
1TT
0T
X 100 (%)0
1
1TT
stretching for T=2s,V1=V2=1500 m/s
Green line assumes
V1=V2
Blue line is for general case,
where V1, V2 can be different
and delT0=0.1s (this case: V1=V2)
Matlab code
Stacking
+ + =
+ + =
Stacking improves S/N ratio
+ =
Semblance Analysis
22
1 1 2
22
1 1 2
22
1 1 2
“Semblance”
+
22
3 33
2 2 2
X
Tw
tt (
s)
+ =
Semblance Analysis
+
X
Tw
tt (
s)
V3
V1
V2
V
Peak energy