Hydro-frac Source Estimation by Time Reversal Mirrors

$Page 1: Hydro-frac Source Estimation by Time Reversal Mirrors$
Hydro-frac Source Estimation by Time Reversal Mirrors

Weiping Cao and C. Boonyasiriwat

UTAM, The University of Utah

Outline

■ Motivation

■ Methodology

■ Numerical Examples

■ Conclusions

Outline

■ Motivation

■ Methodology


■ Conclusions

Motivation

• Hydro-frac is important for oil recovery operations;

• Using time reversal mirror (TRM) method, only a local velocity model near the well needed;

• Potential for super-resolution and super-stacking properties from TRM.

Outline

■ Motivations

■ Methodology


■ Conclusions

Methodology

• TRM imaging;

• Apply TRM imaging to locating hydro-fracs

by wavefield extrapolation;

• Detailed implementation.

TRM Imaging

Time Reversal Mirror

Time

Time

PrimaryPrimary

MultiplesMultiples

Image source location with

natural Green’s functions

No velocity model needed

g

tgtdm )0,|,(),0,|,()( xgsgx

g

tgtdm )0,|,(),0,|,(),( xgsgx

Apply TRM to Locating Hydro-fracs

),|,( sourcettd sg

),|,( sourcettd sg : passive data generated by hydro-fracs

Problem: finding )0,|,( xg tg

Solution: extrapolate VSP or seismic while drilling (SWD) data.

g

tgtdm )0,|,(),0,|,(),( xgsgx

TRM imaging

s

g

Extrapolate VSP or SWD Data to obtain

g

go

x

go

)0,|,( xg tg

g

x

og

o g|xg|ggx )0,,()0,,()0,|,( otgtdtG

Forward extrapolation:

: convolution

og


Backward extrapolation:

: crosscorrelation

Only a local vel. model needed

MethodologySummary for the implementation:

Record VSP or SWD data as natural GF;

Extrapolate VSP or SWD data to obtain semi-natural GFs between surface and image points using the local velocity model near the well;

Cross-correlate these semi-natural GFs to the passive seismic data generated by hydro-fracs.

Outline

■ Motivation

■ Methodology

Numerical Examples

■ Conclusions

Numerical Examples

Synthetic Tests with SEG/EAGE Salt Model:

Hydro-frac imaging with correct source

excitation times;

Hydro-frac imaging with strong background

noise;

Hydro-frac imaging with incorrect source

excitation times;

Synthetic Data Generation

0

3.50 16

Z (

km)

X (km)

SEG/EAGE Salt Model

4 (km/s)

2 (km/s)

Synthetic data: RVSP or SWD data,

Passive seismic gathers

3.2

3.7

Z (

km)

8 12X (km)

3.5

2.5

km/s

Image with Correct Source Excitation Times

TRM imaging with forward extrapolation

Actual hydro-frac location: (10 km, 3.4 km)

2.7

3.2

Z (

km)

8 12X (km)

3.1

2.3

km/s


TRM imaging with backward extrapolation

Actual hydro-frac location: (10 km, 3.01 km)

Image with Strong Background Noise

Synthetic Passive Gather

0

60 15Receiver X (km)

Tim

e (s

)

Noisy Gather: S/N =10,495

0

60 15Receiver X (km)

Tim

e (s

)

Actual hydro-frac source location: (10 km, 3.01 km)


2.7

3.2

Z (

km)

8 12X (km)

1

-0.5

TRM Image from the Noisy Gather


TRM Image from the Noisy Gather: S / N =1 / 10496

2.7

3.2

Z (

km)

8 12X (km)

1

-0.5

Image with Incorrect Source Excitation Times

20 ms advance

3.2

3.7

Z (

km)

8 12X (km)

Exact sourceexcitation time

3.2

3.7

Z (

km)

8 12X (km)

20 ms delay

3.2

3.7

Z (

km)

8 12X (km)

Outline

■ Motivation

■ Methodology


Conclusions

Conclusions

TRM is applied to locate hydro-fracs with VSP or SWD data, and provide accurate images when we use exact source excitation times.

TRM images show strong resilience to white noise.

TRM images are sensitive to source excitation times.

2-D median assumption.

Acknowledgments

We thank the 2007 UTAM sponsors for the support.




2.7

3.2

Z (

km)

8 12X (km)

1

-0.5


2.7

3.2

Z (

km)

8 12X (km)

1

-0.5



3.2

3.7

Z (

km)

8 12X (km)

3.5

2.5

km/s

Interferometric Imaging Implementation

g

xg,sg,x *)()()( Gdm

welldGdG gxg,s,gxg, )()()( well

Step2: Image hydro-fracture sources

Step 1: Extrapolate of VSP data

wellwell dGdG gxg,sgxg, *)(),()(

Outline

■ Motivations

■ Methodology


■ Conclusions

Methodology


■Numerical Examples


■Numerical Examples

0

3.5

0 16

Z (

km)

X (km)

SEG/EAGE Salt Model

Synthetic Seismic Data





original

Subtract 20 for frac(advance)

Plus 20 for frac (delay)





TRM Imaging


Time

Time

PrimaryPrimary

MultiplesMultiples




g

tGtdm )0,|,(),0,|,()( xgsgx

g

tGtdm )0,|,(),0,|,(),( xgsgx

TRM Imaging


Time

Time

PrimaryPrimary

MultiplesMultiples




0)()()( tg

Gdm x|gs|gx

g

Gdtm )()(),( x|gs|gx

Apply TRM to Locating Hydro-fracs

Hydro-frac Location )|( sgd

g

gdtm )()(),( x|gs|gx

)|( sgd : passive data generated by hydro-fracs

Problem: finding ),|,( sourcettg xg

Solution: extrapolate VSP or seismic while drilling (SWD) data.

Extrapolate VSP or SWD Data to obtain

g

go

x

go

)0,|,( xg tg

og


Forward extrapolation:

g

x

og


Backward extrapolation:

convolution

convolution

Outline

■ Motivations

■ Methodology


■ Conclusions

Conclusions

• The summation imaging condition with trial time shifts can effectively image unknown seismic sources with necessary information.

• The super stacking property of this imaging scheme enables reliable source location in the presence of strong random noise.

• Scattered or reflected waves can provide higher resolution for imaging seismic sources than direct waves, especially when receiving aperture is limited.

• The contribution from scattered or reflected waves can be easily masked by the direct waves in the imaging process due to amplitude difference.

Acknowledgments

Thanks to the UTAM sponsors for the financial support

Methodology

Poststack Kirchhoff migration, use only the direct arrivals

g

xgGsgdxm *),(),()(

Image with Incorrect Source Excitation Times

Exact

20 ms advance

20 ms delay

ThanksThanks

Extrapolate VSP or SWD Data

Find Green’s function (GF) between surface and image points near the well by extrapolating VSP or SWD data.

g

go

x

og

o g|xg|ggx )0,,()0,,()0,|,( otGttG d

Forward extrapolation

Methodology

g

go

x

ogo g|xg|ggx )()()|( oGG dBackward extrapolation

Both extrapolations need only local velocity model.

Methodology

g

go

x

ogo g|xg|ggx )()()|( oGG dBackward extrapolation

Both extrapolations need only local velocity model.

Documents

Hydro-frac Source Estimation by Time Reversal Mirrors