Rock and fluid thermodynamics control the dynamics of ... · control the dynamics of induced...
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Rock and fluid thermodynamics control the dynamics of induced
earthquakes
M. Acosta, F. Passelègue, A. Schubnel et M. Violay
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Context – Induced Seismicity in Enhanced Geothermal Systems
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
UNDERSTAND THE MICROPHYSICAL INTERACTIONS BETWEEN PORE FLUID AND RESERVOIR FAULTS DURING INDUCED EARTHQUAKES
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Methods - Experiments
Stick-Slip experiments under Triaxial stress conditions σ1 > σ2 = σ3
Best analogue for earthquakes CONTEXT METHODS RESULTS MODEL IMPLICATIONS
A B
Under review in Nature Communications: Acosta et al. 2017
Samples: 30 ˚ Saw cut westerly granite cylinders (φ=40 mm ; H=88 mm)
Instrumentation:
• External measurements: σ1 ; σ3 ; pf ; ε1
• Internal sensors:
Near fault strain gauges
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Methods- Stick-slip experiments
Under review in Nature Communications: Acosta et al. 2017
Elastic loading until shear strength is reached CONTEXT METHODS RESULTS MODEL IMPLICATIONS
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Results- 100 Hz measurements
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
Pceff=Pc-Pf= 70 MPa Pf held constant during experiment
Under review in Nature Communications: Acosta et al. 2017
Three pore pressure configurations (DRY, Low Pf, High Pf)
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Results- 100 Hz measurements
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
Pceff=Pc-Pf= 70 MPa Pf held constant during experiment
Under review in Nature Communications: Acosta et al. 2017
Three pore pressure configurations (DRY, Low Pf, High Pf)
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Results- 100 Hz measurements
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
Pceff=Pc-Pf= 70 MPa Pf held constant during experiment
Under review in Nature Communications: Acosta et al. 2017
Three pore pressure configurations (DRY, Low Pf, High Pf)
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Results- 100 Hz measurements
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
Pceff=Pc-Pf= 70 MPa Pf held constant during experiment
Under review in Nature Communications: Acosta et al. 2017
Water Pressure ==
Lower coulomb strength.
Three pore pressure configurations (DRY, Low Pf, High Pf)
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Results- Static stress drop .Vs. Slip
CONTEXT METHODS RESULTS MODEL IMPLICATIONS Under review in Nature Communications: Acosta et al. 2017
Pceff=Pc-Pf= 70 MPa Pf held constant during experiment
B
Pore pressure = low static stress drops
Slip [μm]
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Results – Dynamic stress drop
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
B
Under review in Nature Communications: Acosta et al. 2017
Pceff=Pc-Pf= 70 MPa Pf held constant during experiment
Dynamic recording of near fault stress
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1 curve = 1 dynamic event
Results – Dynamic stress drop
CONTEXT METHODS RESULTS MODEL IMPLICATIONS Under review in Nature Communications: Acosta et al. 2017
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Largest dynamic stress drops at Low Pf
Results – Dynamic stress drop .Vs. Slip
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
Slip [μm]
E
Under review in Nature Communications: Acosta et al. 2017
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Results – Dynamic Friction
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
E
F
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14
A B
C D
DRY
Low Pf High Pf X 10 000
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15
A B
C D
DRY
Low Pf High Pf X 10 000
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Asperity temperature model - Description
Flash Temperature = maximum transient temperature responsible for weakening
ΔT
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
Heat source rate Temperature buffering
Ar<<A τa>>τ
A B
Under review in Nature Communications: Acosta et al. 2017
Bowden and Tabor, 1969 Archard, 1959
Violay et al, 2013
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Asperity temperature model - Description
Thermophysical properties of fluid depend on Pressure & Temperature
ΔT
Dependence on P & T !
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
Heat source rate Temperature buffering
Bowden and Tabor, 1969 Archard, 1959
Violay et al, 2013
A B
Under review in Nature Communications: Acosta et al. 2017
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Asperity temperature model - Results
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
A C B
Under review in Nature Communications: Acosta et al. 2017
Heat source rate Temperature buffering
Thermodynamic phase transitions control Temperature rise
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Thermal pressurization model
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
Thermal pressurization accounts for reduction in dynamic friction
- Difference DRY and LOW Pf ??
- Stress drop at HIGH PF ??
THERMAL PRESSURIZATION.
Schmidt, 2007 Rice, 2006;
Sibson, 1973; Lachenbruch, 1980; HEAT & PORE FLUID
Under review in Nature Communications: Acosta et al. 2017
Slip rate m.s-1
B A Vaporization & Flash Heating
Rice, 2006
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CONCLUSIONS. Reduced THERMAL WEAKENING
= THERMAL PRESSURIZATION
THERMAL WEAKENING =
FLASH HEATING (decomposition of contacts)
Enhanced THERMAL WEAKENING
= FLASH HEATING + THERMAL
PRESSURIZATION
Under review in Nature Communications: Acosta et al. 2017
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
Thermodynamics control dynamic weakening processes during earthquake rupture.
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Careful! – σN Evolves with depth! High Depth => Higher stress => FLASH HEATING
Thermophysical properties of water and rock should be taken into account in physics based models
CONTEXT METHODS RESULTS MODEL IMPLICATIONS
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Ddhvac.com
QUESTIONS ?
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Asperity temperature model – Parameter description