advances in the prediction of shear events induced from ...advances in the prediction of shear...

29 Sep 07 - Erice 1

Advances in the Prediction of Shear Events

Induced From Mechanical Stimulation

T. Kohl & T. MégelGEOWATT AG

Dohlenweg 28, CH-8050 Zürich

29 Sep 07 - Erice 2

Contents

EGS site Soultz-sous-Forêts

FE Kernel / HEX-S Reservoir Model

Interpretation GPK3 /Stimulation Forecast of GPK4

Stimulation Planning at Coso EGS Project

29 Sep 07 - Erice 3

INTRODUCING GEOWATT AG

Geothermal Energy utilization

Engineering

Hydrogeology

Numerics

• Resource Evaluation• Generic studies High- and Low-Enthalpy Systems• Courses at University and Engineering Schools

• Dimensioning Heating/Cooling (BHE-Felder)• Reservoir Engineering• Measurements

• Tunneling: Inflow scenario• Flow system

• Coupled 3D-FE calculations• Data bank• Specific simulation tools

29 Sep 07 - Erice 4

European EGS Project Soultz s.F.Location and tectonic setting

Basel

Strasbourg

Karlsruhe

Soultz-sous-Forêts

Major V

osgian

Fault

Wes

t. Rh

ine

Faul

t

Adapted from Genter, 1994

SoultzGPK2,3,4

GPK1

GPK2/GPK3/GPK4

GPK1

29 Sep 07 - Erice 5

EGS Concept(Enhanced Geothermal System)

Production Injection

fractured network

surface Installations

Production: ~3MWe (≈10% Pt)

Natural fractures, artificially enhanced through "hydraulic or chemical stimulation"

29 Sep 07 - Erice 6

EGS - Modeling Approaches

• Essentially fractured medium, Darcy flow; non-Darcy flow at high fluid velocities in fractures

• Hydraulic coupling: advection• Thermal coupling: buoyancy, density, viscosity• Mechanical processes play an important

role in reservoir development and assessmentFracture mechanics

Shear fracturing

Tensile fracturing

Matrix elasticityPoroelasticityThermoelasiticity

• Injected fluid and formation fluids are different;biphasic flow or multicomponent transport

• Geochemistry also play an important role in reservoir characteristics

( ) nc στ ⋅Φ+= tan

pf

f

PSP

SP

⋅++>

+>

ασ

σ

min

min

29 Sep 07 - Erice 7

Hydraulic Stimulations and Microseismicity

• GPK2 Stimulation (July 2000): 14'080 events• GPK3 Stimulation (July 2003): 21'600 events• GPK4 Stimulation (September 2004): 5'753 events• GPK4 Stimulation (February 2005): 2'966 events• GPK4 1st Step rate test (February 2005): 183 events• GPK4 Acidization test (March 2005): 304 events• GPK4 2nd Step rate test (March 2005): 256 events

29 Sep 07 - Erice 8

Soultz - Microseismicity

Seismic Events at GPK2 and GPK3 after 1 day injection

29 Sep 07 - Erice 9

Microseismic Density

Total Stimulation EventsDensity calculated for cube volumes: 50x50x50m3

29 Sep 07 - Erice 10

Analysis of Microseismic Density

Comparison of GPK4 Stimulations:September 2004 February 2005


Indication for Hydromechanical Interaction

Injection Rate and located events GPK3

[h] after 27.05.2003, 12:50

Eve

nts/

hour

Inje

ctio

nra

te[l/

s]

0 10 20 30 40 50 60 70 80 90 100 110 120 1300

50

100

150

200

250

300

350

400

450

500

0

10

20

30

40

50

60

70

© GEOWATT AG CH-Zürich


Stochastic vs. Deterministic Reservoir Models

Deterministic Reservoir Models+ Control of all physical processes- Complex meshing - Simplified geometries

Stochastic Reservoir Models+ Refined representation of fractures/fault zones- Neglecting often matrix interaction- Hybrid approach


FE Code Kernel

ORIGINAL GOAL:Simulation of coupled thermal-hydraulic-mechanical interactions

fully 3-D very versatile code (i.e. transport of radionuclides, chemical subst.)continuously new (linear & non-linear) mechanisms (i.e. turbulence)special treatment of fractures1-D, 2-D & 3-D elements with different shape functionsplatform independent (standard Fortran90)

2

1

3

4

2

1

3

4

5

2

13

4

5

6


FE Code Kernel:Implemented Coupling SchemeHydraulic PRESSURE FIELD

transient Darcynon-linear (fracture aperture, non-Darcian)ρ(T, P) buoyancyμ(T, P)

Thermal TEMPERATURE FIELDtransient diffusion advectionλ(T, P), ρ(T, P)

Matrix Elasticity STRESS FIELDSteady statelinearPoro-ElasticityThermo-Elasticity

Fracture Mechanics FRACTURE APERTUREShearingCompliance


FE Code Kernel:Elastic Matrix Mechanisms

Injection of cold fluid in a hot rock matrix

Thermo-elastic matrix stresses

Injection of pressurised fluid in ambient matrix

Poro-elastic matrix stresses

T3 Δ⋅⋅⋅= TT

ii KS βwith K Bulk modulus

βT coeff. linear expansion

PΔ⋅= BP

iiS αwith αB Biot coeff.


Experience on deterministic H-T-M simulations

X

Y

r 30 years

3D Reservoir4 fracture zonesPoro-Elasticity & Thermo-Elasticity (Kohl, 1995)Normal aperture complianceNo shearing

-> not suited for hydraulic stimulation

Temperature

S22 stress change


3D- Deterministic Fracture GeometryDynamic Long Term Behaviour

Synthetic exampleaperture: a0=200μm

t=10yrs

t=30yrs

-5100 -5050 -5000 -4950y-100

-80

-60

-40

-20

0z

-5-10-15-20-25-30-35-40-45

Situation after 30 yearsΔT [K]

-5100 -5050 -5000 -4950 y-100

-80

-60

-40

-20

0z

Situation after 10 years

-5100 -5050 -5000 -4950-100

-80

-60

-40

-20

0

Darcy-velocity

1 m s-1

-5100 -5050 -5000 -4950-100

-80

-60

-40

-20

02.5E-042.4E-042.3E-042.2E-042.1E-042.0E-04

aperture [m]


New Model: HEX-S

FE algorithm for characterization of massive hydraulic stimulations

3D simulator of hydro-mechanical processesCoupling

→ fracture shear and compliance→aperture variation→Permeability

Mapping deterministic and stochastic fractures to FE grid

(Kohl & Mégel, 2007)


Mechanical Shearing

Penny-shaped cracks with individual slip patches

Coulomb Shear Criteria

Compliance

Jacking Aperture: σn,eff <0

( )( )dilS

s

dilbasiceffn

UaKU Φ⋅=Δ=

Φ+Φ⋅−=Δ

tan;

tan,

τ

σττ

refn

effn

aa

,

,

0

91 σσ⋅+

=


Hydraulic Flow in fractured medium

Full 3D transient hydraulic model

Discretization of borehole with 1-D elements

Mapping of fracture to rock matrix

explicit permeability adjustment

required hydraulic boundary conditions

(here laterally)


'HEX-S' Flow Chart

Model setupPrediction of reservoir development

Stepwise structural interpretationof the microseismic cloud

Stepwise structural interpretationof the microseismic cloud

Mapping of the deterministic structures to a FE-grid

Mapping of the deterministic structures to a FE-grid

Mapping of stochastic structures to the FE-grid

Mapping of stochastic structures to the FE-grid

Pressure development in the reservoir

Pressure development in the reservoir

Adaptation of FE-grid permeability distribution

Adaptation of FE-grid permeability distribution

Shearing and opening of fracturesShearing and opening of fractures

Injection flow foreseenInjection flow foreseen


Discretization 5km Reservoir

Numerical FE GridElement size 25m~400‘000 elementsDepth: 3000-6000 mVertical OH-sectionsLateral borders: Dirichlet BC

-6000

-5000

-4000

-3000

z

-4000

-2000

0

2000

4000

x

-6000

-4000

-2000

0

2000

4000

y

X Y

Z

XY

Z

GPK2

GPK4GPK3


Fracture Data

Deterministic Borehole DataGPK2: Only incomplete UBI measurement to 6 major fracture zones according to BRGM interpretation.GPK3: 11 major fracture zones from UBI log (BRGM)GPK4: 11 major fracture zones from R. Maurer

Deterministic fractured zones4 major planes (1. Interpretation)

Stochastic fractured zones>2000 distributed planes


Soultz Fracture Model

Deterministic slip patches Stochastic realization

GPK2 GPK3 GPK4


Initial apertures:Deterministic / stochastic slip patches

Aperture: "stochastic" slip patches: 20 – 300 μm"deterministic" slip patches generally largerDepending on orientation and depth (stress field)Calibrated with initial borehole transmissivity


First AssessmentGPK3 Stimulation

Stimulation GPK3Focus on major hydraulic injection steps

Fit of downholepressure historyHighly non-linear processesPermeability variation due to shearing

time [s]

dP

dh[P

a]

Flow

rate

[l/s]

0 100000 200000 300000 400000 5000000

2E+06

4E+06

6E+06

8E+06

1E+07

1.2E+07

1.4E+07

1.6E+07

1.8E+07

2E+07

0

10

20

30

40

50

60

70

80

90

100

Measured (depth corr.)ModelFlow

IIdata : 1IImodl : 1

IIdata : 0.78IImodl : 0.88






Identical time constants


Dynamic reservoir processes

Microseismic events GPK3 Simulated shearing GPK3

-1000

0

1000

-2000-1000

01000

-6000

-5000

-4000

-3000

-2000

-1000

0

Easting [m]

t =1 day

Identical spatial constants


Soultz 3D Hydraulic Field

Strongly anisotropic pressure distributionRadial field only around injection pointPressure envelope oriented along fracture orientationPressure wave propagation in areas with highest degree of fracturation

GPK3Open borehole section

5 MPa2 MPa

Pressure distribution around GPK3


Y

X

Z

1.70E+071.60E+071.50E+071.40E+071.30E+071.20E+071.10E+071.00E+079.00E+068.00E+067.00E+066.00E+065.00E+064.00E+063.00E+062.00E+061.00E+06

Reservoir Pressure Distribution

Flow aligned along seismic structures

Seismicity connected to zones of high pressure

Simulated shearing events & pressure distribution GPK3


Modeling Tool HEX-S: Prognosis GPK4 stimulation 04SEP13

Measurement

-5500

-5000

-4500

Depth

0

500

East

ing

-2000-1500-1000

Northing

XY

Z

-6000

-5000

-4000

-3000

x3

-100001000

x1

-2000-100001000x2

OH-sectionmodel

Path of development

Forecast10h

1stDay


Forecast GPK4 stimulation:HEX-S Hydraulic Model

Predicted evolution of shearing events at GPK4 after

Plane View View from West10 hrs stimulation

1 day stimulation

Events are not location-corrected Path of development

OH-sectionmodel


Stimulation of GPK4 (13-16 Sep. 04)Microseismic Locations

Measured evolution of microseismic locations at GPK4

View from West: t= 10h View from West: t= 3 days

XY

Z

Path of development


Modeling Tool HEX-S: Prognosis GPK4 stimulation 04SEP13

Forecast

ΔPdh ≈ 21 MPa for 30l/s additional ΔPdh ≈ 1.5 MPawhen increasing to 45 l/smaximum Pdh at t=15500 sGeneral characterisic:Short transient P-behaviour

Measurements

ΔPdh ≈ 15.5 MPa for 30l/s additional ΔPdh ≈ 1.05 MPawhen increasing to 45 l/smaximum Pdh at t=16’600 sshort transients

time [s]

ΔPdh

[MP

a]

Qin

Om

ega

100000 200000 3000000

5

10

15

20

0

10

20

30

40

50

60

70

80

90

100

Ref.pressure45.0 MPa

time [s]

ΔPdh

[Pa]

0 100000 2000000

5E+06

1E+07

1.5E+07

2E+07

2.5E+07

IImodl : 6.9-7.4 IImodl : 9.7-10.7


Simulation GPK4 Increase of aperture (≅permeab.)

2.7 h 5 h 20 h

36 h 53 h

Iso-Surface = 10 μm


New fracture volume

Flow injection vs. new fracture volume: Injection during simulation period: 6'300m3

Fluid losses over lateral drainage systemsCalculated Volume Change reflects data

30 l/s injection during first 50'000 s: -> 1000 m3

45 l/s during last 12'000 s -> Additional 500 m3

80% of the new fracture volume is generated from compliance ΔV(t) Δa(r) at 10 / 53 hrs

time [s]

ΔPdh

[Pa]

V[%

]

Vto

t[m

3 ]

0 50000 100000 150000 2000000

5E+06

1E+07

1.5E+07

2E+07

2.5E+07

3E+07

0

10

20

30

40

50

60

70

80

90

100

0

500

1000

1500

2000

Model C3

Vc[%]

Vs[%]

Vtot

Injection vs. Volume Change never explicitly

defined


Importance Shear Failure

Percentage of aperture improvement

next to the borehole: up to 70% of the total aperture enhancement.

Predicted displacements in reservoir: max. 1cmnear borehole: up to 1.5cm


Conclusions

HEX-S new hydro-mechanical reservoir modelDeterministic/stochastic fracture distributionDynamic reservoir behavior by joint H-M solution

Requirements:Geological / fracture reconnaissance Stress field

Successful forecast of GPK4 stimulation

Physical Reservoir ModelBased on integrated data analysis


Future Application:

Microseismic impactGeneric studies

• using local reservoir properties• Design calculation to minimize shear displacement

Design of optimum reservoir creation strategiesoptimization of lateral seismic extensionDual vs. single injections

Resolve fundamental questionsMax. flowrate vs. max. volume injection

On Site support during stimulationModel update jointly with seismic recordingMinimizing test duration


Coso Project Area

38 pad38A-938B-938C-9

34-9RD2


Coso EGS site

Borehole trajectoriesopen hole section (thick lines)

-600

-400

-200

0

200

[]

-200 0 200 400

38C-9

38b-9

38a-9

38-9

34-9RD2

-3000

-2500

-2000

-1500

-1000

z[m

]

0

500

x [m]-500

0

y [m]

38C-9

38b-9

38a-9

38-9

34-9RD2

38A-9

38C-938B-9

34-9RD2


34-9RD2

38A/B/C-9

Coso Model:Deterministic FZ in HEX-S model


10 km

Coso Model:Stochastic & Deterministic FZ


Coso:3D Hydraulic Model

Strongly anisotropic pressure distributionRadial field only around injection pointPressure envelope oriented along fracture orientationPressure wave propagation in areas with highest degree of fracturation

Pressure distribution around 34-9 RD2


Coso:First model calculationsPossible development of microseismicity

advances in the prediction of shear events induced from ...advances in the prediction of shear...

Documents