allied geophysical lab research presentations april 2, 2014
DESCRIPTION
Allied Geophysical Lab Research Presentations April 2, 2014. Near-Surface Events… Friend of Foe ?. Fred Hilterman Distinguished Research Professor EAS, University of Houston Chief Scientist Geokinetics Data Processing & Integrated Reservoir Geosciences. Field Record - PowerPoint PPT PresentationTRANSCRIPT
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Allied Geophysical LabResearch Presentations
April 2, 2014
Fred HiltermanDistinguished Research Professor EAS, University of HoustonChief Scientist Geokinetics Data Processing & Integrated Reservoir Geosciences
Near-Surface Events…Friend of Foe ?
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Field Record Typical Interpretation Problem
What are shingles?Are they lateral gaps in the refractor?
Oz Yilmaz
Objective: Provide quantitative insight into how near-surface events are generated. We’ll go the easy way … generate a catalog of synthetics.
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Outline
Elastic syntheticsA. Identify eventsB. Define asymptotes of eventsC. Vary near-surface thicknessD. Vary refractor thickness
Near-Surface Events …
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Half Space
Modeling Philosophy
Start with Simplest model !
Refractor
5600, 0, 2.00
9000, 0, 2.24
ft/s ft/s g/cc850 ft
Half Space
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Half Space
Simplest Acoustic Model
Refractor
5600, 0, 2.00
9000, 0, 2.24
ft/s ft/s g/cc850 ft
Half Space
Source-Receiver Offset
(P1P1)
AcousticVSHEAR = 0
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AirAcoustic Synthetic
AcousticVSHEAR = 0
Refractor
5600, 0, 2.00
9000, 0, 2.24
ft/s ft/s g/cc
P1
PCrit
P2
| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
| || | | |0 ft 5000 ft
850 ft
Half Space
Source-Receiver Offset
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Air
AcousticVSHEAR = 0
Refractor
5600, 0, 2.00
9000, 0, 2.24
ft/s ft/s g/cc
P1
PCrit
P2
| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
| || | | |0 ft 5000 ft
850 ft
Half Space
Source-Receiver Offset
(P1P1)
2(P1P1)
3(P1P1)
4(P1P1)
(P1P1)
2(P1P1)
3(P1P1)
4(P1P1)
(P1P1)(P1P2P1)
(P1P2P1)
2(P1P1)(P1P2P1)
(P1P1)(P1P2P1)
Acoustic Synthetic
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AirTrapped and Leaky Acoustic Modes
AcousticVSHEAR = 0
Refractor
5600, 0, 2.00
9000, 0, 2.24
ft/s ft/s g/cc
P1
PCrit
P2
| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
| || | | |0 ft 5000 ft
PCrit
Leaky Modes
Trapped Modes
850 ft
Half Space
Source-Receiver Offset
PCrit = P12/P2
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Equivalent Elastic ModelAir
Refractor
5600, 2600, 2.00
9000, 3960, 2.24
ft/s ft/s g/cc Elastic850 ft
Half Space
Source-Receiver Offset
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Event Identification – Elastic ModelAir
Refractor
5600, 2600, 2.00
9000, 3960, 2.24
ft/s ft/s g/ccNear Surface
Direct, Rayleigh, ???850 ft
Half Space
AGCSource-Receiver Offset
P1 – Direct ArrivalRayleigh Wave
S1
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
(P1P1)
2(P1P1)
3(P1P1)
4(P1P1)
(P1P1)(P1P2P1)
(P1P2P1)
2(P1P1)(P1P2P1)
Air
Refractor
5600, 2600, 2.00
9000, 3960, 2.24
ft/s ft/s g/cc Reflections: P1P1 Head Waves: P1P2P1
850 ft
Half Space
Source-Receiver Offset
AGC
Event Identification – Elastic Model
Asymptote P1
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s(P1P1)(P1P2S1)
(P1P2S1)
2(P1P1)(P1P2S1)
(P1S1)
(P1P1)(P1S1)
2(P1P1)(P1S1)
3(P1P1)(P1S1)
Air
Refractor
5600, 2600, 2.00
9000, 3960, 2.24
ft/s ft/s g/cc Reflections: P1S1 Head Waves: P1P2S1
850 ft
Half Space
Source-Receiver Offset
AGC
Event Identification – Elastic Model
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
2(S1S1)
(S1P2S1)
(S1S1)
2(P1P1)(S1S1)
(P1P1)(S1S1)
(P1S1)(S1S1)(S
1 S2 S
1 )
Air
Refractor
5600, 2600, 2.00
9000, 3960, 2.24
ft/s ft/s g/cc Reflections: S1S1 Head Waves: S1P2S1
850 ft
Half Space
Source-Receiver Offset
AGC
Event Identification – Elastic Model
Asymptote S1
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Air
Refractor
5600, 2600, 2.00
9000, 3960, 2.24
ft/s ft/s g/cc
(P1P1)
(P1S1)
(S1S1)
(P1P2P1)
(P1P2S1)
(S1P2S1)
(S1S2S1)
P1
24 Event SummaryFour Groups
850 ft
Half Space
Source-Receiver Offset
AGC
Rayleigh
S1
Event Identification – Elastic Model
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Outline
Elastic syntheticsA. Identify eventsB. Define asymptotes of eventsC. Vary near-surface thicknessD. Vary refractor thickness
Near-Surface Events …
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
PCrit
P1
R2 R1
Limits and AsymptotesAir
Refractor
5600, 2600, 2.00
9000, 3960, 2.24
ft/s ft/s g/cc Guided Waves
Ground Roll
R1 .92 S1
R2 .92 S2
PCRIT = P12/P2
SCRIT = S12/S2Guided Waves
(Trapped Modes)
Rayleigh Waves(Ground Roll)
850 ft
Half Space
Source-Receiver Offset
AGC
P2
SCRIT S1
S2
P1 asymptote for all n(P1P1)
S1 asymptote for all n(S1S1)
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Outline
Elastic syntheticsA. Identify eventsB. Define asymptotes of eventsC. Vary near-surface thicknessD. Vary refractor thickness
Near-Surface Events …
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Near Surface Thickness
Thickness = 850 ftRefractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
Air
850 ft
Half Space
Source-Receiver Offset
S1
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
450 ft
Half Space
Air
Thickness = 450 ftRefractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
Near Surface Thickness
S1
Guided waves collectin PCrit-P1 cone Post-critical S-waves
collect in SCrit-S1 Cone
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Thickness = 400 ft400 ft
Half Space
Air
Refractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
Near Surface Thickness
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Thickness = 350 ft350 ft
Half Space
Air
Refractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
Near Surface Thickness
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Thickness = 300 ft300 ft
Half Space
Air
Refractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
Near Surface Thickness
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Air
Thickness = 250 ftRefractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
250 ft
Half Space
Source-Receiver Offset
Near Surface Thickness
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Thickness = 200 ft200 ft
Half Space
Air
Refractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
Near Surface Thickness
S1
Guided waves showphase velocityShear guided waves
appear as ground roll
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Air
Thickness = 150 ftRefractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
150 ft
Half Space
Source-Receiver Offset
Near Surface Thickness
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Air
Thickness = 90 ftRefractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
90 ft
Half Space
Source-Receiver Offset
Near Surface Thickness
S1
Refractions overcomeguided waves inPCrit-P1 cone as P1 layer thins
Long appear inRayleigh cone R1-R2
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
Air
Thickness = 60 ftRefractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
60 ft
Half Space
Source-Receiver Offset
Near Surface Thickness
S1
Post S1S1 and Rayleighmerge in SCrit-R2 cone
As P1 layer thinsrefractions move to P2
P1 and Pcrit effects decrease as upper layer thickness decreases
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Outline
Elastic syntheticsA. Identify eventsB. Define asymptotes of eventsC. Vary near-surface thicknessD. Vary refractor thickness
Near-Surface Events …
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
AirRefractor Thickness Variation
Refractor Thickness = InfiniteRefractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.24
PCrit
P1
R2 R1
P2
SCRIT
60 ft
Half Space
Source-Receiver Offset
S1
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
60 ft
200 ft
AirRefractor Thickness Variation
HalfSpace Refractor thickness decreases, head wave
• loses amplitude• horizontal velocity is constant
Refractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.245400, 2380, 2.21
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
Refractor Thickness = 200 ft
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
60 ft
100 ft
AirRefractor Thickness Variation
HalfSpace
Refractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.245400, 2380, 2.21
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
Refractor Thickness = 100 ft
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| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
60 ft
50 ft
AirRefractor Thickness Variation
HalfSpace
Refractor
5600, 2600, 2.00 ft/s ft/s g/cc
9000, 3960, 2.245400, 2380, 2.21
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
S1
Post-critical S1S1 effects decreaseP2 layer thins,refractions lose amplitude with offset
Refractor Thickness = 50 ft
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Oz Yilmaz
| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
60 ft
50 ftLower LayerRefractor
Upper Layer ShinglingThin Layer over Thin Refractor
AirRefractor Thickness Variation
HalfSpace
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
S1
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Oz Yilmaz
| || | | |0 ft 5000 ft
_
_____________
0s
.5s
1.0s
60 ft
50 ftLower LayerRefractor
Upper Layer ShinglingThin Layer over Thin Refractor
AirRefractor Thickness Variation
HalfSpace
PCrit
P1
R2 R1
P2
SCRIT
Source-Receiver Offset
S1
Shingling • nth Critical-angle reflection (amplitude =1) generates head wave• nth Head wave loses amplitude due to thin refractor layer• nth +1 Critical-angle reflection (amplitude =1) generates head wave• nth + 1 Head wave loses amplitude due to thin refractor layer• Repeat
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Summary: Reflectivity Modeling of Near-Surface EventsVelocity asymptotes “quantify” event cones
• Guided S-waves• Rayleigh waves• Guided P-waves• Refraction arrivals
Shingling and multiple refractions “quantified” by• P-wave and S-wave velocities • Thickness of upper layer and refractor
Lessons from near-surface modelingStart with simplest model and learn with each model variation.
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That’s it!
Thanks for your attention