Rock and fluid thermodynamics control the dynamics of induced earthquakes

Size: px

Start display at page:

Download "Rock and fluid thermodynamics control the dynamics of induced earthquakes"

Winfred Horton
5 years ago
Views:

1 Rock and fluid thermodynamics control the dynamics of induced earthquakes M. Acosta, F. Passelègue, A. Schubnel et M. Violay

2 Context Induced Seismicity in Enhanced Geothermal Systems UNDERSTAND THE MICROPHYSICAL INTERACTIONS BETWEEN PORE FLUID AND RESERVOIR FAULTS DURING INDUCED EARTHQUAKES

3 Methods - Experiments Stick-Slip experiments under Triaxial stress conditions σ 1 > σ 2 = σ 3 A B Samples: 30 Saw cut westerly granite cylinders (φ=40 mm ; H=88 mm) Instrumentation: External measurements: σ 1 ; σ 3 ; p f ; ε 1 Internal sensors: Near fault strain gauges Best analogue for earthquakes

4 Methods- Stick-slip experiments Elastic loading until shear strength is reached

5 Results- 100 Hz measurements Pceff=Pc-Pf= 70 MPa Pf held constant during experiment Three pore pressure configurations (DRY, Low Pf, High Pf)

6 Results- 100 Hz measurements Pceff=Pc-Pf= 70 MPa Pf held constant during experiment Three pore pressure configurations (DRY, Low Pf, High Pf)

7 Results- 100 Hz measurements Pceff=Pc-Pf= 70 MPa Pf held constant during experiment Three pore pressure configurations (DRY, Low Pf, High Pf)

8 Results- 100 Hz measurements Water Pressure == Lower coulomb strength. Pceff=Pc-Pf= 70 MPa Pf held constant during experiment Three pore pressure configurations (DRY, Low Pf, High Pf)

9 Results- Static stress drop.vs. Slip B Slip [μm] Pceff=Pc-Pf= 70 MPa Pf held constant during experiment Pore pressure = low static stress drops

10 Results Dynamic stress drop B Pceff=Pc-Pf= 70 MPa Pf held constant during experiment Dynamic recording of near fault stress

11 Results Dynamic stress drop 1 curve = 1 dynamic event

12 Results Dynamic stress drop.vs. Slip E Slip [μm] Largest dynamic stress drops at Low Pf

13 Results Dynamic Friction E F

14 DRY A B C Low Pf X D High Pf 14

15 DRY A B C Low Pf X D High Pf 15

16 Asperity temperature model - Description Bowden and Tabor, 1969 Archard, 1959 Violay et al, 2013 Ar<<A τa>>τ A B ΔT Heat source rate Temperature buffering Flash Temperature = maximum transient temperature responsible for weakening

17 Asperity temperature model - Description Bowden and Tabor, 1969 Archard, 1959 Violay et al, 2013 A B ΔT Heat source rate Temperature buffering Dependence on P & T! Thermophysical properties of fluid depend on Pressure & Temperature

18 Asperity temperature model - Results A B C Heat source rate Temperature buffering Thermodynamic phase transitions control Temperature rise

19 Thermal pressurization model Rice, Difference DRY and LOW Pf?? - Stress drop at HIGH PF?? THERMAL PRESSURIZATION. A B Vaporization & Flash Heating HEAT & PORE FLUID Schmidt, 2007 Rice, 2006; Sibson, 1973; Lachenbruch, 1980; Slip rate m.s -1 Thermal pressurization accounts for reduction in dynamic friction

THERMAL WEAKENING = FLASH HEATING + THERMAL

20 CONCLUSIONS. Reduced THERMAL WEAKENING = THERMAL PRESSURIZATION THERMAL WEAKENING = FLASH HEATING (decomposition of contacts) Enhanced THERMAL WEAKENING = FLASH HEATING + THERMAL PRESSURIZATION Thermodynamics control dynamic weakening processes during earthquake rupture.

21 Careful! σ N Evolves with depth! High Depth => Higher stress => FLASH HEATING Thermophysical properties of water and rock should be taken into account in physics based models

22 QUESTIONS? Ddhvac.com

23 Asperity temperature model Parameter description

Seismic and aseismic processes in elastodynamic simulations of spontaneous fault slip

Seismic and aseismic processes in elastodynamic simulations of spontaneous fault slip Most earthquake simulations study either one large seismic event with full inertial effects or long-term slip history