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CONSOLIDATION AND CREEP OF A MULTIPHASE HIGH POROUS
CHALK
Priol Grégoire, [email protected]: 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
2. In a air/water system
Subsidence of sea-bed in the North Sea oilfields
Stability and durability of quarry, or natural slope
Ageing of chalk massif
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Presentation plan
Introduction:
Concept tools:
Experiments:
Conclusion:
Waterflooding, compaction and subsidence in Ekofiskoilfields (chalk reservoir)
Similarity with unsaturated soils
Retention properties, suction and capillary pressure in chalk,
Load stages odometer tests
Time dependent behaviour,
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General presentation
Production: 1971-20501986: Injection of sea water
waterfloodingSubsidence: 40 cm/year
Evolution of oil pressure:from 49 MPa to 24 MPa
2000: Subsidence (10 meters)
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Schematic profile
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Suction : so = uo - uw
Soil skeleton
OilWater
Lixhe chalk (Belgium)
Cretaceous (35 million years)Upper Campanian (Hod formation)
Plates of coccolithes (1~10 microns)
n = 38% ~ 41%, rpores= 0.37 µm
Similarity with unsaturated soils
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Testing procedures for unsaturated soils allowing to control suction:
•Overpressure method•Osmotic technique•Mercury Intrusion Porosimetry (MIP)
Oil-water suction so = uo-uw
Capillary and physico-chemical effects between chalk, water and oil
wettability of the chalk
Experimental techniques of suction control
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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
Pompe pneumatique
Atmosphère à humiditérelative contrôlée
Solution saturée
Echantillon
Sels
Dessicateur étanche
20 °C +/- 1°C
4,297K2SO4
8255Mg(NO3)2
Suction (MPa)Humidity (%)Salt
Table 1 : Various types of salt used
wwowo aRTs ln−=−= µµ
0vv uuHR =
Suction control by managing the relative humidity (HR)
HR is controlled viathe salt nature
The technique allows higher suction levels (up to 100 MPa)
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Axis translation method
GDS Eau
Contrôle de la pression d'eau
GDS HuileContrôle de la pression d'huile
Pierre poreuse
EchantillonPierre céramique
-500 0 500 1000 1500
Pression d'huile (kPa)
-1000
-500
0
500
1000
1500
Suc
cion
(kPa
)
pw= 0 kPa
pw= 200 kPa
pw= 500 kPaControl separately of the two pressures (and exchange volumes by mean of a ceramic porous stone that is hydrophilic and lipophobic,
The water pressure is kept constant and positive, in order to work in a larger suction path (<400kPa)
Drainage: water driving by oil
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Retention curves
0 0.2 0.4 0.6 0.8 1Srw
0.01
0.1
1
10
100
1000
10000
100000
succ
ion
(MP
a)
ImbibitionDrainage
0 0.2 0.4 0.6 0.8 1Srw
0.01
0.1
1
10
100
1000
10000
100000
succ
ion
(kP
a)
ImbibitionDrainage
Oil/water System Air/water system
Suc
tion
(kP
a)
Suc
tion
(kP
a)
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0 20 40 60 80 100
WATER SATURATION, Srw (%)
0.001
0.010
0.100
1.000
10.000
SUC
TIO
N, s
(MPa
)
Retention curves of Lixhechalk (oil-water)
OSMOTIC TECHNIQUE(imbibition)
MERCURY INTRUSION POROSIMETRY (drainage)
OVERPRESSURE (drainage)
Retention curve, synthesis
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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 force5 Tonnes
Comparateurs
Piston
Echantillon
Pierre poreuseDéplacement du plateau inférieur contrôlé
au moyen d'une presse pneumatiqueà vitesse de déplacement constant (1 à 50 µm/min)
e.g. Leroueil, Sheahan
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CRS Test (2/4)
10 100 1000 10000 100000σV (kPa)
-0.08
-0.06
-0.04
-0.02
0
Déf
orm
atio
n vo
lum
ique
CRS TestsEau 1µm/minEau 5µm/minEau 10µm/min Eau 50µm/min
Vol
umet
ric s
train
WaterWaterWaterWater
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CRS Tests (3/4)
1E-008 1E-007 1E-006 1E-005 0.0001Vitesse de déformation (s-1)
1000
10000
100000
Lim
ite é
last
ique
(kP
a)
SecHuile200 kPaEau
122,20,0454,499Dry
1,3316,660,0604,451Oil
2,0410,90,0924,516s=200 kPa
2,449,250,1084,462Water
ratiom’1/m’A
Tableau 2: Parameters of the Leroueil law (1985)
Variation of the slope according to the wettability
( ) ( )1log1log εσ &m
Ap ′+=′
Yie
ld s
tress
(kP
a)
Strain rate (s-1)
DryOil
Water
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CRS Test (4/4)
s
σ
dε/dt
Strain rate effects on the suction-yield stress hardening relationship
LC Curve , Alonso et al. (1990)
LC (dε/d
t)
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The odometer test
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.
F=F0
Sample
Porous stone
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Consolidation theory
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). ( )ke1aγhT
t vw2
v
+=
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
0 20 40 60 80 100Temps (j)
0.88
0.92
0.96
1
e/e 0
1E-010
1E-009
1E-008
1E-007
stra
in ra
te
Stage at 14.5 MPaexperimental curveslope (20 points)
αβ −= tee .0
cstettee
+−−=⎟⎟⎠
⎞⎜⎜⎝
⎛)ln(ln 0
0
α
β represents the instantaneous strain,α controls the slope of strain vs time curve
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Parameters’ evolutions
α and β are quite bilinear, and represent well the visco-elastoplastic behaviour.
0 1 2 3Rapport de la Contrainte
sur la contrainte de pré consolidation
0
0.001
0.002
0.003
0.004
0.005A
lpha
0.88
0.9
0.92
0.94
0.96
0.98
1
Bet
a
abβ
β
α
α
σ/σe
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Stress – strain relations
• Results are well ordered with suction (and wettabilitycharacteristics),
• The yield stress is suction dependent
100 1000 10000 100000Axial stress (kPa)
-0.12
-0.08
-0.04
0
Axia
l stra
in
Water saturatedOil saturatedMix saturated s=200kPaDry sample
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Fluids effects
0.8 1.2 1.6 2 2.4Normalized yield stress
0
0.2
0.4
0.6
0.8
1
Wet
tabi
lity
0
5000
10000
15000
20000
25000
Suc
tion
(kP
a)
Fluid wettabilitySample suction (kPa)
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Influence of fluids on creep (1/3)
No significant modification in creep is observed according to the over stress
0 1 2 3 4Οverstress ratio σ/σe
0
0.004
0.008
0.012
0.016
0.02
Cre
ep ra
te p
aram
eter
α
Dry sampleOil saturatedMix saturated s = 200 kPaWater saturated
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Influence of fluids on creep (2/3)
0 400000 800000 1200000 1600000 2000000Time (s)
0.975
0.98
0.985
0.99
0.995
1
e/e 0
Oil saturateds=200 kPaWater saturated
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0 1 2 3 4Οverstress ratio σ/σe
0
0.004
0.008
0.012
0.016
0.02
Cre
ep ra
te p
aram
eter
α
Dry sampleOil saturatedMix saturated s = 200 kPaWater saturated
Influence of fluids on creep (2/3)
0 20 40 60 80Time (days)
0.92
0.94
0.96
0.98
1vo
id ra
tio e
/e0
Axial stress: 19.8 MPaOil saturated (initially)'Water saturated'
Intantaneous collapseunder
water infiltration
α=0,0164
α=0,0047
Water injection divided σe by 2
α increases by a factor of 5
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Mechanism of water injection
100 1000 10000 100000Axial stress (kPa)
-0.12
-0.08
-0.04
0
Axia
l stra
in
Water saturatedOil saturatedMix saturated s=200kPaDry sample
Water injection
Strength decrease
Creep (strain)
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Application to an other chalk (1/3)
100 1000 10000 100000Contrainte verticale (kPa)
0.75
0.8
0.85
0.9
0.95
1In
dice
des
vid
es n
orm
é e/
e 0
Essai secEssai s=1500kPaEssai saturé
•Detritic chalk withglauconite,
•Density: 2,74 Mg/m3
•Porosity: 37%
•Average pore radius: 700 nm:
Craie d’Estreux
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Application to an other chalk (2/3)
0 1 2 3 4 5σ/σe
0
0.005
0.01
0.015
0.02
0.025
α
EausecSuccionSuction
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Application to an other chalk (3/3)
0 1 2 3 4σ/σe
0
0.005
0.01
0.015
0.02
0.025α
EstreuxLixhe The behaviour is very
close to the oilfied chalk one,
Viscosity seems to be strongly connected to water content.
Dry chalk is less viscous.
In both system (oil/water, air/water), chalk can potentially collapse due to physicochemical mechanisms
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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 behaviourof 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 fluidessur le comportement différé de la craie, XXIIème Rencontres universitaires de génie Civil, Marne-la-Vallée.