1. Potential impact of faults on CO2 injection into saline aquifers & Geomechanical concerns of CO2 injection into depleted oil reservoirs
Quentin Fisher, Sergey Skachkov
Suleiman Al-Hinai, Carlos Grattoni
School of Earth and Environment, University of Leeds

2. Outline 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

3. Impact of faults on gas production
(from van der Molen et al., 2003
EAGE conference on seals, Montpellier)

4. Fault 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)

5. Intrareservoir faults in the PermoTrias

6. Cataclastic faults

7. Cataclasites

8. Multi-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

9. Sorby multi-phase flow laboratory

10. Relative 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

11. Eclipse simulation of C02 injection into saline aquifer

12. Eclipse simulation of C02 injection into saline aquifer

13. Eclipse simulation of C02 injection into saline aquifer

14. Geomechanics

15. Conditions for leakage along hydrofractures
Pore pressure needs to overcome minimum horizontal stress while leakage occurs
From Nordgård Bolås and Hermunrud, 2003

16. Stress path – Pp/Sh 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

17. Stress path – Pp/Sh 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

18. Stress 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)

19. Conclusions
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

20. Future/on-going work

21. Stress arching
Geomechanical methods for estimating leakage nearly always assume Sv stays constant
This ignores stress arching

22. 4D-seismic and stress arching
From Minkoff et al., (2004)

23. IPEGG – Technological Position
Calculate
seismic
attributes
Create coupled
stress – flow
software 3D
Built based on simulation grid
User friendly
Large range of constitutive models
Local grid capabilities to allow modelling of well bore stability c
4D response
Anisotropy
Microseismicity
Groundtruth
with field data
JIP between Leeds, Bristol and Rockfield Software Ltd
Sponsored by BP, BG, ENI and Statoil
Use to forward
model for
predictions

24. Geomechanical/Seismic Coupling Benchmarks
Geometry
Rectangular Reservoir 22,000ft x 11,000ft * 250 ft
Quarter Symmetry Model
Output - Pressure
Wellbore
Thin Reservoir – Single Phase Flow

25. Geomechanical/Flow Coupling Thin Reservoir Example
Dean at al., 2003
Fully Implicit Dynamic Relaxation/Transient
Top of Reservoir
Surface
Contours of Subsidence after 4000 days Dynamic Relaxation/Transient Coupling Strategy
ELFEN Fully Coupled

26. Elfen-Seismic elastic models
Elasticities
Elfen-Seismic elastic models
2525
3185
Example P-wave velocities calculated using Elfen output
based on Gassman’s equation