allied geophysical lab research presentations april 2, 2014

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 ?

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.

Outline

Elastic syntheticsA. Identify eventsB. Define asymptotes of eventsC. Vary near-surface thicknessD. Vary refractor thickness

Near-Surface Events …

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

| || | | |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

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

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

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

| || | | |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

| || | | |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

| || | | |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

| || | | |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

| || | | |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

| || | | |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

Outline

Elastic syntheticsA. Identify eventsB. Define asymptotes of eventsC. Vary near-surface thicknessD. Vary refractor thickness

Near-Surface Events …

| || | | |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)

Outline

Elastic syntheticsA. Identify eventsB. Define asymptotes of eventsC. Vary near-surface thicknessD. Vary refractor thickness

Near-Surface Events …

| || | | |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

| || | | |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

| || | | |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

| || | | |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

| || | | |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

| || | | |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

| || | | |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

| || | | |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

| || | | |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

| || | | |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

Outline

Elastic syntheticsA. Identify eventsB. Define asymptotes of eventsC. Vary near-surface thicknessD. Vary refractor thickness

Near-Surface Events …

| || | | |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

| || | | |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

| || | | |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

| || | | |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

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

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

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.

That’s it!

Thanks for your attention