the effect of ﬂuid injection on an experimental fault and its ... ••• methods •••...

The effect of fluid injection on an experimental fault and its role on frictional stability and earthquake triggering

Scuderi M.M.1, Collettini C.1,2 and C. Marone3

European Research CouncilSeventh Framework Programme

“Ideas” Starting GrantGLASS: 259256

European Union Horizon 2020 research and innovation programme

Marie Sklodowska-Curie FEAT No. 656676

1 La Sapienza University of Rome 2 Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome

3 Pennsylvania State University, USA

Introduction •••

Methods •••

Results - RSF ••

Results - fault slip ••••

Results - fault porosity •

Discussion •••••

Summary

Important to understand the interaction between fluids and faulting

Val D`Agri oil field, Italy Wastewater-induced seismicity (ML > 2)

Seismicity relates to main peaks in the well-head injection pressure and shows a migration

on a pre-existing fault confined within the Apulian carbonates.

Improta et al., 2015 GRL

Oklahoma, USA Wastewater-induced seismicity (many events Mw > 5)

Wastewater injection increased seismicity rate dramatically

Keranen et al., 2014 Science

Fault Reactivation vs. Frictional Slip Stability

The increase in fluid pressure along a fault will decrease the effective normal stress that clamps the fault in place favoring fault reactivation

Hubbert and Rubey, 1959 Bull. Geol.Soc. Am

ΔPf

Failure Criteria

FaultReactivation

Shea

r Str

ess (τ)

Effective normal stress (σ’n)

τ = µ (σn - Pf )

σnτ

kck

Fault Stress Profile

Pf

Wastewater Injection

Impermeable Layer

AncientFault

Acquifer

Fluid Pressure

(Pf )

Fault Clampingstress (σ‘n)

Pf

ΔPf

k/Kc>1<1 Unstable

Stable

CarbonateReservoir


Methods •••





Summary

Criterion for fault Stabilitydefined by the critical stiffness (kc)

kc= (σn - Pf)(b-a) / Dck > kc k ~ kc k < kc Stable Conditionally

Stable

Unstable

Upon reactivation fault slip behavior can be described via the Rate- and State- Frictional Properties:

(1) potentially seismic (Velocity Weakening)

(2) aseismic (Velocity Strengthening)

σnτ

kck

Fault Stress Profile

Pf

Wastewater Injection

Impermeable Layer

AncientFault

Acquifer

Fluid Pressure

(Pf )

Fault Clampingstress (σ‘n)

Pf

ΔPf

k/Kc>1<1 Unstable

Stable

CarbonateReservoir

Coeffi

cien

t of F

rictio

n (µ

)

a ln (v/v0)

(a-b) ln (v/v0)

DC

Displacement

Velocity Strengthening

Velocity Weakening

b ln (v/v0)

Slow Fast


Methods •••





Summary

Fault Reactivation vs. Frictional Slip Stability

Biaxial Apparatus in a Double Direct Shear configuration

within a Pressure Vessel

Collettini et al., 2014 IJRM; Scuderi and Collettini, 2016 Nature Scientific Report


Methods •••





Summary

Up-streamPpu

Down-streamPpdShear

stress

Normal stress

Porous Frits

Latex tubes

Latex boots

O-RingGouge Layers

Double Direct Shear configuration within a pressure vessel

Sample assembly

Conduits for fluids

Porous FritsLatex jacket

5.5 cm

5cm


Methods •••





Summary

Double Direct Shear configuration within a pressure vessel

Sample assembly

Conduits for fluids

Porous FritsLatex jacket

5.5 cm

5cm


Methods •••





Summary

Experimental curve for a typical experiment

0.1 - 100 µm/s

Scuderi & Collettini, 2016 Nat. Sci. Rep.


Methods •••





Summary

Scuderi & Collettini, 2016 Nat. Sci. Rep.

The friction rate parameter (a-b) decreases as the pore fluid pressure is increased

The parameter Dc decreases as pore fluid

pressure is increased from sub-hydrostatic to near lithostatic conditions

Critical Slip Distance - Dc

Velocity dependence of friction (a-b)

-0.002

0

0.002

0.004

0.006

0.008

0.01

0 5 10 15

v = 0.1 - 1 m/sv = 1 - 10 m/sv = 10 - 100 m/s

(a-b)

Effective Normal Stress (σ’n), MPa

λ = Pf / σn

Marble GougePc = 19 MPa

0 5 10 15 20

0.10.20.30.40.50.60.70.80.9

0

20

40

60

80

100

120

0 5 10 15

0.10.20.30.40.50.60.70.80.9


λ = Pf / σn

Criti

cal S

lip D

istan

ce (D

c), µ

m

v = 0.1 - 1 m/sv = 1 - 10 m/sv = 10 - 100 m/s

Marble GougePc = 19 MPa

Pf increase

Pf increase


Methods •••





Summary

sub-hydrostaticNear lithostatic

Creep experiments

Constant Normal stress

Constant Shear stress

We monitor fault slip

Pc is constant

Pf is increased stepwise

Scuderi et al., 2017 EPSL

Shea

r Str

ess (

τ), M

Pa

Time, minutesU

p-St

ream

flui

d pr

essu

re, M

Pa

Constant PfInjection 1MPa/hInjection 0.2MPa/12min

λ = 0.4λ increases

(1) (2) (3) Creep test

Steady State Shear Strength (τss)90% τss

80% τss

Failure

(1) Constant displacement rate of 10 µm/s to localize shear

(2) Fault relaxation to residual strength

(3) Set the shear stress at the desired value in load control to monitor fault slip


Methods •••





Summary

Shea

r Str

ess (

τ), M

Pa

Time, minutesU

p-St

ream

flui

d pr

essu

re, M

Pa

Constant PfInjection 1MPa/hInjection 0.2MPa/12min

λ = 0.4λ increases

(1) (2) (3) Creep test

Steady State Shear Strength (τss)90% τss

80% τss

13151719Fluid Pressure, MPa

Perm

eabi

lity,

m2

Shea

r Str

ess (

τ), M

Pa


τ = 0.19 + 0.55 σ’n

(1)

creep test

Failure Envelope

Failure

Creep experiments

Three types of experiments to characterize fault slip behavior:

1) Constant Pf to monitor undisturbed fault creep 2) Injection of fluids at 1 MPa every hour 3) Injection of fluids at 0.2 MPa every 12 min


Methods •••





Summary

Creep Experiments - 90%𝛕ss

An increase in pore fluid pressure

causes fault reactivation and failure with fault slip reaching slip velocities of

1 to 2 mm/s

1) Primary creep least for 35-40min in the experiment before injection begun

2) Secondary creep aseismic creep at v~50nm/s corresponding to strain rates of 2×10-4 s-1

3) Tertiary creep begin when we meet the criterion for reactivation the acceleration preceding dynamic failure least for ~1h

Scuderi et al., 2017 EPSL


Methods •••





Summary

90%𝛕ss 80%𝛕ss


Methods •••





Summary

(1-2) During aseismic creep fault gouge compacts (3) Accelerated fault creep is associated with dilation (4) During co-seismic slip fault gouge undergo compaction

Fault zone deformation characterized by:

90%𝛕ss 80%𝛕ss


Methods •••





Summary

1MPa/h

0.2MPa/12min

1MPa/h0.2MPa/12min

Fault Reactivation vs. Frictional Slip StabilityThe conundrum of fluid overpressure in earthquake triggering

Rate- and State- Friction analysis shows that at the same applied stress field and for similar values of

pore fluid factor, 𝜆, the fault has velocity strengthening behavior (i.e. aseismic behavior).

Creep tests show that over pressurized fluids cause accelerated creep leading to dynamic

instability once the criterion for fault reactivation is met.


Methods •••





Summary

Energy balance for a representative unit volume of fault gouge(Marone et al., 1990; Bos&Spiers, 2002)

Micro-mechanical model for fault zone deformation

τ = τ x +dhdδ

σ n −Pf( )

τ = τ x +dεdγ

σ n −Pf( )dεdγ

dhdδ

For our experimental configuration

Shear Stressduring creep experiments is imposed at constant values

represents the sum of all microscale dissipative processes per unit volume that include grain fracture, frictional sliding of grain contacts, pressure solution and crystal plasticity.

Volumetric variations per unit of slip

Effective Stress


Methods •••





Summary

τ = τ x +dhdδ

σ n −Pf( )

stage (2) stage (3) stage (4)

σn

τ=const.

Pf Pf

∆h

Energy dissipation by dilation slip velocity increase

stage (3)

Dynamic SlipCompaction

Energy balance for unit volume of fault gouge(Marone et al., 1990; Bos&Spiers, 2002)

Constant

Increases due to microscale dissipative

processes such as pressure solution

Constant

To maintain the energy balance fault gouge

compacts



Methods •••





Summary

τ = τ x +dhdδ

σ n −Pf( )Constant



σn

τ=const.

Pf Pf

∆h


stage (3)



The effective stress decreases due to fault

pressurization causing a energy imbalance

The fault must dilate to dissipate the

energy


Methods •••





Summary

τ = τ x +dhdδ

σ n −Pf( )Constant



σn

τ=const.

Pf Pf

∆h


stage (3)



Fault dilation is no longer an efficient mechanism for energy dissipation, the fault

system reacts with fracturing and shear localization resulting in dynamic slip

propagation.


Methods •••





Summary

Pore fluid pressurization can promote accelerated fault slip in fault gouge that is characterized by velocity strengthening behavior (i.e. aseismic creep).

Fault slip behavior is well described by an energy balance that consider the interaction between fault zone deformation and surrounding stress field .

Summary:

Thank youMail: [email protected]

The duality between the rate strengthening behavior and the observed nucleation of dynamic instability can be interpreted by considering the different dynamics of micro mechanical processes and stress state evolution between creep experiments and constant displacement rate experiment used to retrieve RSF parameters.

mailto:[email protected]?subject=

Pore fluid pressurization can promote accelerated fault slip in fault gouge that is characterized by velocity strengthening behavior (i.e. aseismic creep).

Fault slip behavior is well described by an energy balance that considers the interaction between the fault zone deformation and the surrounding stress field .

Summary:

Thank youMail: [email protected]

The nucleation of dynamic instability on a rate strengthening fault can be due to the different dynamics of micro mechanical processes and stress state evolution between creep experiments and constant displacement rate experiment that are used to retrieve RSF parameters.

mailto:[email protected]?subject=

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