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 E-mail: quentin@rdr.leeds.ac.uk

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

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

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)

Intrareservoir faults in the PermoTrias

Cataclastic faults

Cataclasites

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

Sorby multi-phase flow laboratory

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

Eclipse simulation of C02 injection into saline aquifer

Eclipse simulation of C02 injection into saline aquifer

Eclipse simulation of C02 injection into saline aquifer

Geomechanics

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

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

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

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)

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

Future/on-going work

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

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

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

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

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

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