Étude in-situ des interactions hydromécaniques entre fluides et failles Application au laboratoire du rift de Corinthe. Ð O À N Mai Linh Institut de Physique du Globe de Paris. Fault slip. Fluid pressure Build-up. Fluid Pressure decrease. Fluid-fault interactions.
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Étude in-situ des
interactions hydromécaniques
entre fluides et failles
Application au laboratoire du rift de Corinthe
ÐOÀN Mai Linh
Institut de Physique du Globe de Paris
Fault slip
Fluid pressure
Build-up
Fluid Pressure
decrease
Example of fluid-fault hydromechanical coupling:
Fault-valve mechanism (Sibson70)
Fault closed
Lots of
theory and
laboratory
works
After Matthai (1992)
I Presentation of the Gulf of Corinth
and the DGLAB project
II Characterization of the hydraulic setting
III A peculiar kind of hydraulic transients:
Events triggered by far earthquakes
I Presentation of the Gulf of Corinth
and the DGLAB project
II Characterization of the hydraulic setting
III A peculiar kind of hydraulic transients:
Events triggered by far earthquakes
subduction
shear zone
extension
Rift of Corinth
Pindos
Gavrovo-
Tripolitza
Greece
Complicated
geodynamics
Complex
geology
From Jolivet (2005)
1.5cm/yr
Aigio fault
1-3cm of slip
After Koukouvelas (1998)
After Bernard (1997)
0.9±0.1MPa
karst
South
North
0.5±0.1MPa
K=0.9-2 10-18m²
(Song,2004)
Impervious fault
(Giurgea, 2004)
Double porosity model
Results to
be taken
with caution
Bulk properties
Matrix properties
Drawdown [m]
Hydraulic tests by GFZ – July 2003
Permanent regime
Dupuit formula
Q~600m³/h
k=1-1.5 10-5 m/s
No storativity
Tides
Log10(Pressure [MPa])
2 absolute pressure gauges
- high precision
- low precision
1 relative pressure gauge
- hydrophone
Log10(Frequency [Hz])
I Presentation of the Gulf of Corinth
and the DGLAB project
II Characterization of the hydraulic setting
III A peculiar kind of hydraulic transients:
Events triggered by far earthquakes
Pressure
Pressure (Bar)
UT Time
Resolution better than 1%
The pressure is similar to that of the karst
The karst dominates the measured pressure
Tidal
calibration
Tidal
calibration
Long-term
fluctuations
How sensitive is the pressure signal to deformation ?
What are the
dimensions
of the aquifers ?
How water
flows through
the aquifers ?
Thermal
Regime
Trizonia
(Aigio)
Temeni
Also
Triple origine
Aigion
Linear regression on the input data
Ouput: pressure in Aigio
Input: Tide gage in Trizonia
Input: Barometric pressure in Temeni
Input: Theoretical tidal strain in Aigio
dP=2.748 10-4 dhoc – 1.784 10-4 dter
No offset
Bad weather at the end of the year 2003
Observed pressure (detided)Û Atmospheric pressure
Poroelastic model (large wavelengths)
B : Skempton coefficient
Ku : Undrained bulk modulus
u : Undrained Poisson ratio
: Barometric efficiency
=0.3±0.1
B Ku=17±1GPa
Water flux
S
Aig10
N
¯¯ Oceanic load ¯¯
Loading profile at a depth of 700m induced by a unit load
σxx+σzz/2ρgh
AIG10
Distance to southern shore (m)
The oceanic load should induce a phase lag !
S
Aig10
N
¯¯ Oceanic load ¯¯
Aigio
fault
Helike
fault
Can the presence of impervious faults explain
this absence of phase lag ?
Analytical prediction of phase lag
for a 1D aquifer with impervious boundaries
S
N
N
Map of semi-diurnal phase lag (°) for a semi-infinite ocean
Phase lag
[-5 min 5min]
ß
[-2.5° 2.5°]
L
x/L
Tidal
calibration
Long-term
fluctuations
Tidal
calibration
Tidal
calibration
Long-term
fluctuations
How sensitive is the pressure signal to deformation ?
Poroelastic parameters
→ excellent « strain » sensor
Karst confined
in a NS direction.
By Aigio fault ?
What are the
dimensions
of the aquifers ?
Storativity
→ Hydraulic
diffusivity
How water
flows through
the aquifers ?
Thermal
regime
Pressure
Flow between
the two
previously
independent
aquifers
No
sharp
seasonal
variations
14 kPa
Pressure (bar)
Time
1 year
Axisymmetric response for infinite aquifers
Pressure (bar)
Time (day)
Axisymmetric analytical solutions
Finite aquifers
Transients controlled by the radii of the aquifers and borehole radius
1. Finite Element Method 2D
to describe flow
in upper and lower aquifers
2. Manual coupling at a
well node (0.1D)
Same pressure
Mass conservation of fluid
distance of the well radius
Can the decrease in pressure observed during the first 3 months
provide constraints on the dimensions of the aquifers ?
Rectangular-shaped aquifers 4 unknowns
Hydraulic properties of the upper aquifer 1 unknown (storativity)
2 pieces of information to fit : amplitude and duration of the drop
Try to find plausible configurations
Too small
Too slow
Upper aquifer: LNS=1000m LWE=200m
Lower aquifer: LNS=5000m LWE=?
Pressure (bar)
Pertinence of
The homogeneous
Model for the karst ?
Time (days)
Long-term
fluctuations
Thermal
regime
Tidal
calibration
Tidal
calibration
Long-term
fluctuations
Poroelastic parameters
→ excellent « strain » sensor
Karst confined
in a NS direction
Both aquifers
are confined
Hydraulic
diffusivity
(Almost) no flow
Storativity
→ Hydraulic
diffusivity
Thermal
Regime
1 year
after drilling
Temperature (°C)
Depth (m)
=
50±10 mW/m2
~22°C/km
zt
Tt
770m
Tmes
H>600 m
Gavrovo-Tripolitza nappe
Fault vertical offset=150m
zt-770m <150m
qb= 70mW/m²
qb=100mW/m²
qb=200mW/m²
Relation Ttzt
from extrapolation of
Thermal gradient
H > 400 m
Temperature (°C)
30
30.2
30.4
30.6
30.8
31
31.2
31.4
31.6
31.8
700
But the introduction of the
karst convection does.
710
720
Depth (m)
500
730
Karst in
conduction
1000
740
Karst in
convection
1500
0
10
20
30
40
50
60
Temperature (°C)
Heat generated by fault slip
does not explain this anomaly
Tidal
calibration
Tidal
calibration
Long-term
fluctuations
Poroelastic parameters
→ excellent « strain » sensor
Hydraulic
diffusivity
Internal advection
Hydraulic
diffusivity
(Almost) no flow
Both aquifers
are confined
Both aquifers
are confined
Large vertical extension
Thermal
regime
Low heat flow
50±10 mW/m²
I Presentation of the Gulf of Corinth
and the DGLAB project
II Characterization of the hydraulic setting
III A peculiar kind of hydraulic transients:
Events triggered by far earthquakes
~10minute-long
~2minute-long
10-200 Pa
10-200 Pa
~100 events/yr
~20 events/yr
Pressure
~2minute-long
~30minute-long
10-400 Pa
50-60 Pa
~200 events/yr
2 events/yr
Only associated with
teleseismic transients
Time
Much earlier than
other published
triggered events
November, 17th 2003
06:43 UTC
Drop of 60 Pa
(equivalent to 3.5nstr)
BKu~17GPa
determined from tidal analysis
30min
5min
Strain>10-8
2003
Rat Island
Event
Magnitude
Strain<10-8
Distance to epicenter (km)
After Montgomery and Manga (2003)
Anomalous drop on pressure data only
h<5nstr
Trizonia
Aigio
LF signal
0 10km
Sacks-Evertson
Strainmeter
STS2
broad-band
Seismometer
(North component)
Comparison of seismic oscillations
of both «deformation» sensors
Nyquist frequency
of the pressure
sensor
P
Frequency
h
- Strainmeter
- Pressure
Good correlation of both sensors
Time
One single wellhead value
Average of pressure
anomaly
along the borehole
Poroelastic response
HETEROGENEOUS
along the borehole
Fault movement
Average of pressure along the borehole
induced by a double-couple located at (x,y)
M0=DS
Map of Log10(Pressure anomaly) for D×S=1m3
x
y
S= slip area
D= relative displacement
Dip direction
z
x
y
Distance from borehole
~ √hydraulictrelaxation
D×S~1m3
<5000m3 (Trizonia data)
Hydrophone
Close-up
Pressure
UTC Time 07:07:02
07:15
07:10
07:05
07:05
07:10
07:15
Hydrophone
+0.000
+0.100
07:05
07:10
07:15
Time
Average of pressure along the borehole
induced by a double-couple located at (x,y)
Map of Log10(Pressure anomaly) for D*S=1m3
Not seen by pressure sensor D*S<0.1-1m3
z
x
x
y
y
Fault plane
Slickensides
Below Nyquist frequency
Data acquisition problem Irregular sampling
Pressure
in Aigio
December, 26th 2004
00:58 UTC
P
S
Strain
in Trizonia
Hydraulic characterisation of AIG10
ÞSensitive “strain” sensor
and internal convection within the karst
but is it the case below the Pindos nappe
Hydraulic characterisation of AIG10
It is now possible to model
the wellhead pressure response to
fault movement
within an homogeneous poroelastic framework
Hydraulic anomalies
The DGLAB project provides the opportunity
to study
dynamic fluid-fault interactions
Hydraulic anomalies
dynamically triggered by S waves from a teleseism,
with a concomitant local microseismic event
Interpretation of the remaining hydraulic events
Expected full instrumentation
0 m
Hydrophone
Installation of the
whole instrumentation
scheduled in
March 2006
Hydrophone
700 m
High-precision
pressure gage
750 m
High-precision
pressure gage
870 m
3C Seismometer
1000 m
S = uniaxial storativity11= 22=0, d33=0
S = unstrained storativity =0
S = strained storativity d=0
S SS
S= (1-αB) S
0.9±0.1MPa
karst
0.5±0.1MPa
Simple optimistic model :
Čermák model
T>1000 yr
(In accordance
with the absence of
Tritium in water)
900
800
Tidal
calibration
Tidal
calibration
Long-term
fluctuations
Thermal
regime
Tides
Log10(Pressure [MPa])
2 absolute pressure gauges
- high precision
- low precision
1 relative pressure gauge
- hydrophone
Log10(Frequency [Hz])
Analytical axisymmetric solutions
shows that the transitory regime
is partly controlled by
the borehole radius
1. Finite Element Method 2D
on each aquifer
2. Manual coupling at a
well node (0.1D)
distance of the well radius
Hydraulic characterisation of AIG10
ÞSensitive “strain” sensor
but internal convection within the karst
but is it the case below ?
Hydraulic anomalies
dynamically triggered by S waves from a teleseism,
with concomitant a local seismic event