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: quentin@rdr.leeds.ac.uk

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

Impact of faults on gas productionImpact of faults on gas production

(from van der Molen et al., 2003EAGE conference on seals, Montpellier)

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)

Intrareservoir faults in the PermoTrias

Cataclastic faultsCataclastic faults

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

)

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

Sorby multi-phase flow laboratorySorby multi-phase flow laboratory

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)

Eclipse simulation of C0Eclipse simulation of C022 injection injection

into saline aquiferinto saline aquifer

Eclipse simulation of C0Eclipse simulation of C022 injection injection

into saline aquiferinto saline aquifer

Eclipse simulation of C0Eclipse simulation of C022 injection injection

into saline aquiferinto saline aquifer

GeomechanicsGeomechanics

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

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

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

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)

• 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

Future/on-going workFuture/on-going work

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

4D-seismic and stress arching4D-seismic and stress arching

From Minkoff et al., (2004)

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

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

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

Elfen-Seismic elastic modelsElfen-Seismic elastic models

2525

3185

Example P-wave velocities calculated using Elfen output based on Gassman’s equation

Elasticities