consolidation and creep of a multiphase porous chalk

CONSOLIDATION AND CREEP
OF A MULTIPHASE HIGH POROUS
CHALK
Priol Grégoire, [email protected]
Direction: De Gennaro V., Delage P.
Ecole Nationale des Ponts et Chaussées (ENPC-CERMES)
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Problematic
The weakening effects due to a modification of the water content
1. In a oil/water system
Subsidence of sea-bed in the
North Sea oilfields
2. In a air/water system
Stability and durability of quarry,
or natural slope
Ageing of chalk massif
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Presentation plan
Introduction:
Waterflooding, compaction and subsidence in Ekofisk
oilfields (chalk reservoir)
Concept tools:
Similarity with unsaturated soils
Experiments:
Retention properties, suction and capillary pressure
in chalk,
Load stages odometer tests
Time dependent behaviour,
Conclusion:
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General presentation
Production: 1971-2050
1986: Injection of sea water
waterflooding
ÎSubsidence: 40 cm/year
Î
Evolution of oil pressure:
from 49 MPa to 24 MPa
2000: Subsidence (10 meters)
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Schematic profile
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Similarity with unsaturated soils
Suction : so = uo - uw
Lixhe chalk (Belgium)
Cretaceous (35 million years)
Upper Campanian (Hod formation)
Soil skeleton
Plates of coccolithes (1~10 microns)
n = 38% ~ 41%,
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rpores= 0.37 µm
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Oil
Water
6
Experimental techniques of suction control
Oil-water suction so = uo-uw
Capillary and physico-chemical effects between chalk, water and oil
wettability of the chalk
Testing procedures for unsaturated soils allowing to control suction:
•Overpressure method
•Osmotic technique
•Mercury Intrusion Porosimetry (MIP)
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The osmotic method
The osmotic method is based on the
used of semi permeable membranes
which permit to reach suction levels
below 1500 kPa
Polythene sheet
PEG solution
Soil sample
Semi-permeable membrane
Magnetic stirrer
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Vapour phase
Salt
Humidity (%)
Suction (MPa)
Mg(NO3)2
55
82
K2SO4
97
4,2
s o = µ wo − µ w = − RT ln a w
HR = u v u v 0
Table 1 : Various types of salt used
Pompe pneumatique
Atmosphère à humidité
relative contrôlée
Dessicateur étanche
Solution saturée
Echantillon
Suction control by
managing the relative
humidity (HR)
HR is controlled via
the salt nature
The technique allows
higher suction levels
(up to 100 MPa)
Sels
20 °C +/- 1°C
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Axis translation method
Pierre poreuse
Contrôle de la pression d'huile
Drainage: water driving by oil
GDS Huile
Echantillon
Pierre céramique
GDS Eau
Contrôle de la pression d'eau
pw= 0 kPa
1500
pw= 200 kPa
The water pressure is kept constant
and positive, in order to work in a
larger suction path (<400kPa)
Succion (kPa)
Control separately of the two pressures
(and exchange volumes by mean of a
ceramic porous stone that is
hydrophilic and lipophobic,
1000
pw= 500 kPa
500
0
-500
0
500
1000
1500
Pression d'huile (kPa)
-500
-1000
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Retention curves
100000
100000
Imbibition
Drainage
10000
10000
1000
succion (kPa)
Suction
(kPa)
succion(kPa)
(MPa)
Suction
1000
100
10
1
100
10
1
0.1
0.1
0.01
0.01
0
0.2
0.4
0.6
0.8
1
Srw
0
0.2
0.4
0.6
0.8
1
Srw
Oil/water System
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Imbibition
Drainage
Air/water system
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Retention curve, synthesis
10.000
Retention curves of Lixhe
chalk (oil-water)
OSMOTIC TECHNIQUE
(imbibition)
MERCURY INTRUSION
POROSIMETRY (drainage)
SUCTION, s (MPa)
1.000
OVERPRESSURE (drainage)
0.100
0.010
0.001
0
20
40
60
80
100
WATER SATURATION, Srw (%)
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Viscous mechanical behaviour
• Odometer tests: Strain rate effects and
creep effects
– CRS Tests,
– Stage loading tests,
• Triaxial tests: study of the “3D” behaviour
– Effects of the pores fluid,
– Suction effects on the yield surface,
– Loading rate effects on the yield surface,
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Constant Rate of Strain tests (1/4)
Barre fixe
Capteur de force
5 Tonnes
Comparateurs
Piston
Echantillon
Pierre poreuse
Déplacement du plateau inférieur contrôlé
au moyen d'une presse pneumatique
à vitesse de déplacement constant (1 à 50 µm/min)
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e.g. Leroueil, Sheahan
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CRS Test (2/4)
0
Déformation
volumique
Volumetric
strain
-0.02
-0.04
CRS Tests
-0.06
Water
Eau
Water
Eau
Water
Eau
Eau
Water
1µm/min
5µm/min
10µm/min
50µm/min
-0.08
10
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100
1000
σV (kPa)
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10000
100000
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CRS Tests (3/4)
A
Limite stress
élastique(kPa)
(kPa)
Yield
100000
Sec
Dry
Huile
Oil
200 kPa
Eau
Water
1/m’
m’
ratio
4,462 0,108
9,25
2,44
s=200 kPa 4,516 0,092
10,9
2,04
Oil
4,451 0,060 16,66
1,33
Dry
4,499 0,045
Water
22,2
1
Tableau 2: Parameters of the Leroueil law (1985)
10000
Variation of the slope
according to the
wettability
1
′
log σ p = A + log(ε&1 )
m′
( )
1000
1E-008
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1E-007
1E-006
1E-005
-1
Vitesse
de déformation
Strain
rate (s ) (s-1)
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0.0001
16
CRS Test (4/4)
Strain rate effects on the suction-yield stress hardening relationship
s
dε/dt
LC
t)
d
/
ε
(d
σ
LC Curve , Alonso et al. (1990)
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The odometer test
F=F0
Sample
Porous stone
Several odometer test have been
performed by submitting chalk
samples to series of load. Notably,
one was suction controlled (200
kPa); and attention was mainly paid
on consolidation and creep.
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Consolidation theory
2
Tv h γ w a v
t=
(1 + e)k
av : compressibility 1-4 10-6 kPa-1
k: permeabilities ranges between
2-5 10-8 m.s-1 (water) and 6.10-9
(oil).
Thanks to the above equation, the dissipation time ranges about 1- 100
seconds.
It seems likely that the low compressibility of the soil skeleton (bonding)
and the permeability of the soft rock are sufficient in chalk to prevent
excess pore fluid pressure generation (Lade and de Boer 1997).
No significant generated pore pressure, mainly
diffused strain corresponds to creep
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Creep model
⎛e⎞
ln⎜⎜ ⎟⎟ = −α ln(t − t0 ) + cste
⎝ e0 ⎠
Stage at 14.5 MPa
experimental curve
slope (20 points)
1
1E-007
e
= β .t −α
e0
0.96
strain rate
e/e0
1E-008
0.92
1E-009
0.88
β represents the
instantaneous strain,
α controls the slope of strain
vs time curve
1E-010
0
20
40
60
80
100
Temps (j)
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Parameters’ evolutions
0.005
1
β
b
0.004
α
0.98
a
0.96
α
0.94
0.002
0.92
0.001
0.9
0
β
Beta
Alpha
0.003
α and β are quite
bilinear, and represent
well the viscoelastoplastic behaviour.
0.88
0
1
2
3
Rapport de la Contrainte
sur la contrainte de pré consolidation
σ/σe
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Stress – strain relations
Axial stress (kPa)
1000
10000
100
100000
0
• The yield stress is
suction dependent
-0.04
Axial strain
• Results are well
ordered with suction
(and wettability
characteristics),
-0.08
Water saturated
Oil saturated
Mix saturated s=200kPa
Dry sample
-0.12
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1
25000
0.8
20000
0.6
15000
Fluid wettability
Sample suction (kPa)
0.4
10000
0.2
Suction (kPa)
Wettability
Fluids effects
5000
0
0
0.8
1.2
1.6
2
2.4
Normalized yield stress
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Influence of fluids on creep (1/3)
0.02
Dry sample
Oil saturated
Mix saturated s = 200 kPa
Water saturated
No significant
modification in
creep is observed
according to the
over stress
Creep rate parameter α
0.016
0.012
0.008
0.004
0
0
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2
Οverstress ratio σ/σe
3
4
24
Influence of fluids on creep (2/3)
1
0.995
Oil saturated
s=200 kPa
Water saturated
e/e0
0.99
0.985
0.98
0.975
0
400000
800000
1200000 1600000 2000000
Time (s)
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Influence of fluids on creep (2/3)
1
Intantaneous collapse
under
water infiltration
void ratio e/e0
0.96
Dry sample
Oil saturated
Mix saturated s = 200 kPa
Water saturated
0.016
Creep rate parameter α
α=0,0047
0.98
0.02
0.012
0.008
0.004
α=0,0164
0
0
0.94
0.92
20
40
2
Οverstress ratio σ/σe
3
4
Water injection divided σe by 2
Axial stress: 19.8 MPa
Oil saturated (initially)
'Water saturated'
0
1
60
80
α increases by a factor of 5
Time (days)
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Mechanism of water injection
100
Axial stress (kPa)
1000
10000
100000
0
Water injection
-0.04
Axial strain
Strength decrease
Creep (strain)
-0.08
Water saturated
Oil saturated
Mix saturated s=200kPa
Dry sample
-0.12
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Application to an other chalk (1/3)
1
Indice des vides normé e/e0
0.95
0.9
0.85
Craie d’Estreux
•Detritic chalk with
glauconite,
Essai sec
Essai s=1500kPa
Essai saturé
0.8
•Density: 2,74 Mg/m3
•Porosity: 37%
0.75
100
1000
10000
Contrainte verticale (kPa)
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•Average pore radius: 700 nm:
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Application to an other chalk (2/3)
0.025
Eau
sec
Succion
Suction
0.02
α
0.015
0.01
0.005
0
0
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1
2
σ/σe
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4
5
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Application to an other chalk (3/3)
0.025
Estreux
Lixhe
The behaviour is very
close to the oilfied chalk
one,
0.02
Viscosity seems to be
strongly connected to
water content.
α
0.015
Dry chalk is less viscous.
0.01
In both system (oil/water,
air/water), chalk can
potentially collapse due
to physicochemical
mechanisms
0.005
0
0
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1
2
σ/σe
3
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CONCLUSION
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Conclusions (1)
• Retention properties of chalk have been clearly
identified for the couple oil and water,
• As for clays, retention is not only governed by
capillarity,
• This results should be taken carefully, because chalk
used in this study has not known oil before (it is not
the case in the reservoir which would change
wettability).
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Conclusions (2)
• Odometer s test confirmed the collapsible behaviour
of oilfield chalk submitted to water injection
• Fluids do not seem to have a influence in the viscous
behaviour considering that: creep rate remains equal
taken into account of the over stress ratio,
• These last remarks warn us against comparing suction
controlled tests at different loading rate despite a
good drainage and good suction control,
• Also, several tests in an air/water saturated chalk have
confirmed the chalk sensitivity to water, and the
coupling between creep and suction .
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Thank you for your kind attention
Further information: [email protected]
De Gennaro V., Delage P., Priol G., Collin F. & Cui Y.-J. 2004. On the collapse behaviour of oil
reservoir chalk, Géotechnique 54 n°6 pp. 415-420.
De Gennaro V., Delage P., Priol G., Sorgi C., Collin F. (2005). Multiphase viscous behaviour of
two different outcrop chalks, XIème IACMAG, Turin,
Priol G., De Gennaro V., Delage P., Sorgi C., Candel Hernandis J.V. (2004) Influence des fluides
sur le comportement différé de la craie, XXIIème Rencontres universitaires de génie Civil, Marnela-Vallée.
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