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Potential impact of faults on COPotential impact of faults on CO22
injection into saline aquifersinjection into saline aquifers&&
Geomechanical concerns of CO2 Geomechanical concerns of CO2 injection into depleted oil reservoirsinjection into depleted oil reservoirs
Quentin Fisher, Sergey SkachkovSuleiman Al-Hinai, Carlos Grattoni
School of Earth and Environment, University of Leeds
E-mail: [email protected]
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OutlineOutline
• Faults and fluid flow
• Relative permeability of fault rocks
• Simulations of CO2 injection into faulted saline aquifer
• Stress path in re-inflated reservoirs
• Ongoing/future research into geomechanicals of CO2 injection
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Impact of faults on gas productionImpact of faults on gas production
(from van der Molen et al., 2003EAGE conference on seals, Montpellier)
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Fault Seal Types in SiliciclasticsFault Seal Types in Siliciclastics
Juxtaposition seal(by far the most common type of barrier to production in heterolithic reservoirs)
Fault rock seal(fault seal sensu stricto – important for Rotliegend)
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Intrareservoir faults in the PermoTrias
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Cataclastic faultsCataclastic faults
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CataclasitesCataclasites
1500
2000
2500
3000
3500
4000
4500
0.00001 0.0001 0.001 0.01 0.1 1 10
Fault permeability (mD)M
ax
imu
m b
uri
al
de
pth
(m
)
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Multi-phase flow properties of faultsMulti-phase flow properties of faults
• Above gas water contact two phases may be present in the pore space
• This lowers the permeability to both gas and water
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Sorby multi-phase flow laboratorySorby multi-phase flow laboratory
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Relative permeability resultsRelative permeability results
• Sw altered using centrifuge and humidity chambers
• Relative permeability of faults as a function of height above FWL (assuming petroleum and brine densities of 0.5 and 1 g/cm3)
• Research into practise within 6 months
01000200030004000500060007000
0.001 0.01 0.1 1
krg
Hei
gh
t ab
ove
FW
L (
ft)
0200400600800
100012001400
0.001 0.01 0.1 1
Krg
gas
-wat
er P
c (p
si)
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Eclipse simulation of C0Eclipse simulation of C022 injection injection
into saline aquiferinto saline aquifer
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Eclipse simulation of C0Eclipse simulation of C022 injection injection
into saline aquiferinto saline aquifer
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Eclipse simulation of C0Eclipse simulation of C022 injection injection
into saline aquiferinto saline aquifer
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GeomechanicsGeomechanics
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Conditions for leakage along Conditions for leakage along hydrofractureshydrofractures
• Pore pressure needs to overcome minimum horizontal stress while leakage occurs
From Nordgård Bolås and Hermunrud, 2003
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Stress path – PStress path – Ppp/S/Shh coupling coupling
• If Mohr circle didn’t change shape during overpressure development then shear fractures would always form
• Poroelastic effect means that Shmin increases with Pp
No Pp/Sh coupling
Pp/Sh coupling
Pp/Sh coupling
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Stress path – PStress path – Ppp/S/Shh coupling coupling
• Knowledge of stress path is needed to predict likelihood and type of failure during both depletion and inflation
• From Hettma et al., (1998) – SPE 63261
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Stress path during re-inflationStress path during re-inflation
• Estimates of stress path have been made from repeated leak-off tests during depletion
• Some evidence shows that stress paths are lower during inflation than deflation (i.e. fracture pressure is lower)
From Santarelli et al., (SPE, 47350)
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• Intrareservoir faults could cause significant barriers to CO2 injection into saline aquifers but are less likely to affect the movement of the brine
• Fracture gradient may be lower than virgin pressure when re-injecting CO2 into depleted reservoirs
• Project up and running to further investigate geomechanics of reservoirs and to predict seismic properties in stress sensitive reservoirs
ConclusionsConclusions
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Future/on-going workFuture/on-going work
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Stress archingStress arching
• Geomechanical methods for estimating leakage nearly always assume Sv stays constant
• This ignores stress arching
R eservo ir
su rface
com paction
S tre tch ing andreduction in v v
Increase in
In cresed sh ears tress
C asingsub ject toshear
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4D-seismic and stress arching4D-seismic and stress arching
From Minkoff et al., (2004)
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IPEGG – Technological PositionIPEGG – Technological Position
Calculate seismic
attributes
Create coupled stress – flow
software
Groundtruth with field data
Use to forward model for predictions
• 3D• Built based on
simulation grid• User friendly• Large range of
constitutive models• Local grid capabilities
to allow modelling of well bore stability
• 4D response• Anisotropy• Microseismicity
c
• JIP between Leeds, Bristol and Rockfield Software Ltd
• Sponsored by BP, BG, ENI and Statoil
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Geomechanical/Seismic CouplingGeomechanical/Seismic Coupling Benchmarks Benchmarks
Thin Reservoir – Single Phase Flow
Geometry
• Rectangular Reservoir 22,000ft x 11,000ft * 250 ft
• Quarter Symmetry Model
Wellbore
Output - PressureOutput - Pressure
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Geomechanical/Flow CouplingGeomechanical/Flow CouplingThin Reservoir ExampleThin Reservoir Example
Contours of Subsidence after 4000 daysDynamic Relaxation/Transient Coupling Strategy
Dean at al., 2003
0
1
2
3
4
5
6
7
8
0 500 1000 1500 2000 2500 3000 3500 4000
Time (Days)
Su
bsi
den
ce (
ft) Top of Reservoir
Surface
Fully Implicit Dynamic Relaxation/Transient
ELFEN Fully Coupled
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Elfen-Seismic elastic modelsElfen-Seismic elastic models
2525
3185
Example P-wave velocities calculated using Elfen output based on Gassman’s equation
Elasticities