Institute of Geophysics, Academy of SciencesInstitute of Geophysics, Academy of SciencesPrague,Prague, Czech RepublicCzech Republic

JanJan Šílený Šílený

Shear-tensile/implosion source model Shear-tensile/implosion source model vs. vs. mmomentoment tensor: tensor: benefit in single-azimuth monitoringbenefit in single-azimuth monitoring

Simulation of Cotton Valley Simulation of Cotton Valley cconfigurationonfiguration

Outline:Outline:

Inversion for MT: Cotton ValleyInversion for MT: Cotton Valley

MT summary: advantages, pitfallsMT summary: advantages, pitfalls

MT alternative: STI MT alternative: STI (shear-tensile/implosion)(shear-tensile/implosion)

reprocessing of Cotton Valleyreprocessing of Cotton Valley

ConclusionConclusion

Motivation: Motivation: hydrofracturing of oil/gas wellshydrofracturing of oil/gas wells

Hydrofracturing of oil/gas wellsHydrofracturing of oil/gas wells

treatment welltreatment well

monitoring wellmonitoring well

monitoring wellmonitoring well

Hydrofracturing of oil/gas wellsHydrofracturing of oil/gas wells

Possibility to recover MT Possibility to recover MT (6 components)(6 components)

far field:far field:3 3 (or more)(or more) wells: wells: OK OK from P, P+Sfrom P, P+S

2 wells:2 wells: OK OK from P+Sfrom P+S

1 well:1 well: Not enough !Not enough !• additional constraint neededadditional constraint needed

VavryVavryčuk čuk (2007)(2007)

JechumtJechumtálová álová & Eisner& Eisner (2008)(2008)

• near-field needednear-field neededSongSong & Toksoz& Toksoz (2011)(2011)

• a simpler source model neededa simpler source model needed

less parameters, e.g. shear +off-plane comp.less parameters, e.g. shear +off-plane comp.

rarelyrarely

occasionallyoccasionally

standardstandard

SourceSource mechanism by fiting seismograms mechanism by fiting seismograms/amplitudes/amplitudes

Troubles causing the uncertainty• noise in the waveforms

• inexact hypocenter location

• inexact earth modelimproperGreen’sfunction

• sparse station distribution

MT

Micro-earthquakes Micro-earthquakes induced by hydrofracturinginduced by hydrofracturing

Cotton Valley Cotton Valley gas fieldgas field hydrofracturehydrofracture experimentexperiment

Rutledge et al. 2004Rutledge et al. 2004

0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 0.21

-2

0

2

4

6

8

10

12

14

16

18

x 10-7

0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16

-4

-2

0

2

4

6

8

10

12

14

16

x 10-8

0.02 0.04 0.06 0.08 0.1 0.12

-4

-2

0

2

4

6

8

10

12

14

16

x 10-7

DC 28%CLVD(P) 11%ISO(impl) 61%

DC 48%CLVD(T) 47%ISO(expl) 5%

DC 35%CLVD(P) 18%ISO(expl) 47%

Data examples:Data examples:vs. volumetricvs. volumetric

P

P

P

S

S

S

deviatoricdeviatoric

sourcesource

G1

R7

G2

Cot

ton

Val

ley

mec

hani

sms

Cot

ton

Val

ley

mec

hani

sms

Šílený, J., Eisner, L., Hill, D. & Cornet, F., 2009. Non-double-couple mechanisms of microearthquakes induced by hydraulic fracturing. J. Geophys. Res., 114, doi:10.1029/2008JB005987.

tensile fracturing successful treatment

Hydrofracturing of oil/gas wellsHydrofracturing of oil/gas wellsCotton Valley case studyCotton Valley case study

= even-determined inversion for MT= even-determined inversion for MT

Viewpoint of fracture mechanics:Viewpoint of fracture mechanics:MT is unnecessarily complexMT is unnecessarily complex

No over-determination !No over-determination !

Far field P+S from 2 wellsFar field P+S from 2 wells

Question of particular interest:Question of particular interest:

Was permeability of the reservoir increased?Was permeability of the reservoir increased?i.e, were tensile cracks created?i.e, were tensile cracks created?

discriminate between shear and tensile modes of fracturingdiscriminate between shear and tensile modes of fracturing

shear slipshear slip tensile cracktensile crack

100% DC

crack closurecrack closure

66% CLVD(T) + 33% ISO(expl)

66% CLVD(P) + 33% ISO(impl)

Prospects:Prospects:

shear slip + tensile crack / cavity closure

BUT too general

MT … general dipole source

includes unphysical sources

Traditional decomposition ISO+DC+CLVDmotiv: • split isotropic and deviatoric part

• single out DCISO DC+CLVD BUT there is something

in addition, namely CLVD

an unphysical sourcephysical sources of interest are combinations of ISO and CLVD

shear – tensile / implosion source model shear – tensile / implosion source model

+ /

benefits:benefits:• physical source• less parameters

disadvantage:disadvantage:• non-linearity

advantage in inversion

(4 angles + magnitude)

advantage: linearity

Dufumier & Rivera 1997Vavrycuk 2001

off-planeangle

66% CLVD(T) + 33% ISO(expl)

66% CLVD(P) + 33% ISO(impl)

tensile crack / cavity closure traditional intuitive explanation(opening crack with fluid influx)is incorrect !

an alternativean alternativeto the MTto the MT

Shear-tensile/implosion source modelShear-tensile/implosion source model

Parameters: • DC angles dip, strike, rake

• off-plane angle • magnitude (scalar moment)

Inversion method: 2-step grid search

• coarse grid global search • fine grid local refinement

advantageous mapping of model space:

at ‘each’ point (in terms of the sampling) information available on the goodness of fit: chi-square

possibility to construct a confidence region:

subspace in the model space around estimated solutionwith a priori specified probability content

Histogram of values of the off-planeangle of the mechanismswith NRMS < NRMSthreshold

Tensile/implosion part

estimate of uncertainty in the tensile/implosion part

positive tensile fracturing negative implosion

Plots of ‘confidence zones’Plots of ‘confidence zones’

Shear-tensile/implosion source modelShear-tensile/implosion source model

Projection of T,P,N axesof the mechanismswith NRMS < NRMSthreshold

DC part of the mechanism

estimate of uncertainty in the DC part orientation

Cotton Valley Cotton Valley gas field hydrofracturegas field hydrofracture experimentexperiment Simulation of a single-well Simulation of a single-well

monitoringmonitoring

two-well vs. single well monitoringtwo-well vs. single well monitoringSynthetic testing of STI:Synthetic testing of STI:

Source Source model:model:

• vertical strike-vertical strike-slipslip• 454500 dip-slip dip-slip

vertical strike-vertical strike-slipslip off-plane off-plane

angleangle tensile cracktensile crack shear slipshear slip

off-plane off-plane angleangle

tensile cracktensile crack shear slipshear slip

454500 dip- dip-slipslip

MT: noise, velocity mismodeling, mismodeling+mislocation

strike-slip + tensile (50 off-plane) dip-slip + tensile (50 off-plane)

model model

mismodeling mismodeling+ mislocation

mismodeling mismodeling+ mislocation

modelmismodelingmismodeling+ mislocation

modelmismodelingmismodeling+ mislocation

noise10% 30%

noise10% 30%

Inversion of data from two monitoring wells

T

P

T

T

T

T

T

TT

T

T

T

P

PP

P

PP

P

P

P

STI: velocity mismodeling

strike-slip + tensile (50 off-plane)

dip-slip + tensile (50 off-plane)

we

ak

mis

mo

de

ling

-20 -10 0 10 20 30 40 500

20

40

60

-20-10 0 10 20 30 40 50 60 70 80 900

200

400

600

stro

ng

mis

mo

de

ling

120,150,200% NRMS

-20 -10 0 10 20 30 40 500

20

40

60

-20-10 0 10 20 30 40 50 60 70 80 900

500

1000

two

wells

singl

e wel

l

two

wells

singl

e wel

lm

odel

mod

el

-20 -10 0 10 20 30 40 500

500

1000

1500

-20 -10 0 10 20 30 40 500

500

1000

1500

-20 -10 0 10 20 30 40 500

50

100

-20 -10 0 10 20 30 40 500

20

40

we

ak

mis

mo

de

ling

stro

ng

mis

mo

de

ling

two

wells

singl

e wel

l

two

wells

singl

e wel

l

120,150,200% NRMS

T

TT

TTTT

T

T

T

P P

PP

P

PP

PP

P

STI: velocity mismodeling + mislocation

strike-slip + tensile (50 off-plane)

dip-slip + tensile (50 off-plane)

stro

ng

mis

mo

de

ling

120,150,200% NRMS

two

wells

singl

e wel

lm

odel

mod

el

stro

ng

mis

mo

de

ling

two

wells

singl

e wel

l

120,150,200% NRMS

-20 -10 0 10 20 30 40 500

50

100

-20-10 0 10 20 30 40 50 60 70 80 900

500

1000

1500

-20 -10 0 10 20 30 40 500

100

200

-20 -10 0 10 20 30 40 500

100

200

T

P

T

T

TT

T

P

P

PP

P

1 2

3

4

56

7

8 910 11

12

STI: noise contamination 10%, 20%

strike-slip + tensile (50 off-plane)

dip-slip + tensile (50 off-plane)

no

ise

10

%n

ois

e 2

0%

two

wells

singl

e wel

l

two

wells

singl

e wel

lm

odel

mod

el

no

ise

10

%n

ois

e 2

0%

two

wells

singl

e wel

l

two

wells

singl

e wel

l

T

P

T

TT

T

T

TT

TT

P

PP

P

PP

PP

P

STI: noise contamination 30%, 40%

strike-slip + tensile (50 off-plane)

dip-slip + tensile (50 off-plane)

no

ise

30

%n

ois

e 4

0%

two

wells

singl

e wel

l

two

wells

singl

e wel

lm

odel

mod

el

no

ise

30

%n

ois

e 4

0%

two

wells

singl

e wel

l

two

wells

singl

e wel

l

T

P

T

T

T

T

TT

TT

T

P P

P PPP

PP

P

Re-processing of Cotton Valley: G1

MT STI

map

vie

wde

pth

view

Ez

N

EN

z

E

N

z

EN

z

T,N

,P a

xes

off-

plan

e

NRMS < 0.9 NRMS < 0.8 NRMS < 0.7

G1 composite

angle (degs)-30 -20 -10 0 10 20 300

50

100

angle (degs)-30 -20 -10 0 10 20 300

500

1000

1500

angle (degs)-30 -20 -10 0 10 20 300

2000

4000

6000

R5

MT STI

map

vie

wde

pth

view

Ez

N

EN

z

Ez

N

E

z

N

G2 composite

MT STI

map

vie

wde

pth

view

Ez

N

EN

z

Ez

N

EN

z

G3 composite

MT STI

map

vie

wde

pth

view

EN

z

Ez

N

E

N

z

EN

z

G4 composite

MT STI

map

vie

wde

pth

view

Ez

N

EN

z

Ez

N

EN

z

SHmax

G4

Red group

~10 m

Conclusions:Conclusions:MT: general description of a dipole sourceMT: general description of a dipole sourcetoo general in case of a simple fracturing:too general in case of a simple fracturing:

hydrofracturing in oil/geothermal industry:hydrofracturing in oil/geothermal industry:

additionaladditional constraint helpful constraint helpful STI modelSTI model

non-linear model non-linear model exploration exploration

opening/closing of tensile cracksopening/closing of tensile cracks

butbut

(e.g., grid search)(e.g., grid search)

advantage in estimateadvantage in estimate

of the solutionof the solution

beneficial in deficient configurationsbeneficial in deficient configurations

robust even with:robust even with: in particular,in particular, single-well monitoring single-well monitoring

less parametersless parameters than MT (5 vs. 6)than MT (5 vs. 6)

of model spaceof model space in in estimate of uncertaintyestimate of uncertainty

• reasonable noise in datareasonable noise in data • realistic mislocationrealistic mislocation• slight velocity mismodelingslight velocity mismodeling

Acknowledgements:Acknowledgements:

Institute of Geophysics, Institute of Geophysics, Academy of Sciences, PragueAcademy of Sciences, PragueCzech RepublicCzech Republic

EC FP7EC FP7 EC FP7 IAPP Project AIM“Advanced Industrial Microseismic

Monitoring”

Grant agreement No.230669

Grant AgencyGrant Agencyof the Czech Republicof the Czech Republic

Grant agreement No.205/09/0724

Project “Non-double-couple mechanisms – – a tool for monitoring the mode of fracturing”