FAST: A New Approach to Risking isking FAST: A New Approach to R Fault Reactivation and Related Seal Breach Fault Reactivation and Related Seal Breach Scott Mildren & Richard Hillis & Richard Hillis Scott Mildren APCRC, NCPGG, The University of Adelaide, Australia The University of Adelaide, Australia APCRC, NCPGG, AAPG Hedberg Hedberg Research Research Confere Conferenc nce, e, AAPG Barossa Valley, South Australia, 1- -5 December 2002 5 December 2002 Barossa Valley, South Australia, 1 A U S T R A L I A N P E T R O L E U M C O O P E R A T I VE R E S E A R C H C E N T R E
FAST: Fault Analysis Seal Technology FAST: Fault Analysis Seal Technology � dead faults and live faults � structural permeability � FAST methodology � Timor Sea examples � discussion and conclusions
Dynamic Seal Breach: Timor Sea HRDZs HRDZs Dynamic Seal Breach: Timor Sea O’Brien & Woods (1995)
Dynamic Seal Breach: Timor Sea HRDZs HRDZs Dynamic Seal Breach: Timor Sea O’Brien & Woods (1995)
Hydrocarbon Seals Hydrocarbon Seals Membrane Caprock Fracture (Hydraulic) Sealing Faults Seals Fault Juxtaposition Other Hydrodynamic after Watts (1987)
Hydrocarbon Seals Hydrocarbon Seals Membrane Caprock Fracture Sealing Faults Dead faults Seals Fault Juxtaposition Live Fracture/React faults Other Hydrodynamic Jones et al. (2000)
Dead Faults Dead Faults or Live Faults? or Live Faults?
Fault- -Valve Model Valve Model Fault Fault reactivation post-charge leads to breaching of the seal Sibson (1992)
Effectiveness of Fracture Permeability Effectiveness of Fracture Permeability 30 cm Fracture Aperture 0.25 mm 30 cm 30 cm D m 1 mD 0 1 5 3 1 Matrix Permeability 1 mD Matrix Permeability 1 mD Ave. Permeability 1 mD Ave. Permeability 13 510 mD
Failure Modes Failure Modes
Rock Failure Rock Failure
Structural Permeability Structural Permeability Failure Mode Criterion Condition P p = σ 3 +T ( σ 1 - σ 3 )<4T Tensile (hydraulic) P p = σ n +(4T 2 - τ 2 )/4T 4T<( σ 1 - σ 3 )<6T Tensile/shear P p = σ n +(C i - τ )/ µ i ( σ 1 - σ 3 )>6T Shear P p = σ n +(C s - τ )/ µ s Shear reactivation - Stylolite ? fine-grained matrix Sibson (1996)
Rock Failure Rock Failure
Sibson (1996) Structural Permeability Structural Permeability
Cosgrove (1995) Structural Permeability: Mesoscale Mesoscale Structural Permeability:
Ferrill & Morris (2002) Structural Permeability Structural Permeability
Pore Pressure & Stress: Central North Sea Pore Pressure & Stress: Central North Sea Gaarenstroom et al. (1993)
Hydraulic Seals and Hydrocarbon Retention Hydraulic Seals and Hydrocarbon Retention Capacity, Central North Sea Capacity, Central North Sea > σ 3 + T P p = σ 3 - P p R c ~ LOP-RFT R c σ 3 σ 2 σ 1 Gaarenstroom et al. (1993)
In Situ Stress and Fracture Permeability In Situ Stress and Fracture Permeability Barton et al. (1995)
In Situ Stress and Fracture Permeability In Situ Stress and Fracture Permeability Barton et al. (1995)
Yucca Mountain Yucca Mountain • Is Yucca Mountain, Nevada, a suitable site for a spent nuclear fuel and high-level radioactive waste repository? repository?
Dilation Tendency Dilation Tendency Dilation tendency is controlled by the magnitude of the normal stress σ 1 −σ n T d = σ 1 −σ 3 Shear Stress Normal σ 3 σ n σ 2 σ 1 Stress Ferrill et al. (1999)
Slip Tendency Slip Tendency Slip tendency is defined as the ratio of shear stress to normal stress σ s T s = σ n Shear Stress σ s Normal σ 3 σ n σ 2 σ 1 Stress Ferrill et al. (1999)
Slip and Dilation Tendency Slip and Dilation Tendency Ferill et al. recognise both modes of failure, but • no consideration of rock properties • separate analyses for each mode of failure
Fault Analysis Seal Technology (FAST) Fault Analysis Seal Technology (FAST) In Situ Fault Stress Polygons Tensor Centreline Mohr's Failure With Circle Envelop Dip Structural Segment Permeability Fault Developmen FAST Map
FAST I FAST I ISS FP MC FE CD SP SF FAST σ H max = 82 MPa σ h min = 46 MPa σ v = 64 MPa Po = 28 MPa σ H orient. = 156°N
FAST II FAST II Cataclasites in Pretty Hill Formation, Banyula-1, Otway Basin 60 ISS FP Shear Stress (MPa) MC FE CD µ SP SF 40 FAST τ = C + µσ n ' 20 τ = 5.4 + 0.78 σ n ' C 0 20 40 60 80 Effective Normal Stress (MPa)
FAST III FAST III ISS FP MC FE CD SP SF FAST σ h ’ σ v ’ σ H ’
FAST IV FAST IV σ H max = 82 MPa RP RP 1.0 σ h min = 46 MPa 0.9 σ v = 64 MPa 0 30 Po = 28 MPa 330 0.8 σ H orient. = 156°N 0.7 60 300 0.6 90 270 0.5 0.4 120 ISS FP 240 0.3 MC FE CD 150 210 0.2 180 SP SF 0.1 FAST σ Hmax = 156 ο N 0.0
polygons to centreline CD FP SF FAST Collapse fault FE SP ISS MC FAST V FAST V Acquired from seismic
0.5 0.0 1.0 FAST VI FAST VI CD FP SF FAST FE SP ISS MC
Evidence for Seal Breach in the Timor Sea Evidence for Seal Breach in the Timor Sea HC Residual Column Column Field HRDZ Sniffer ALF Integrity Heights Heights (m) (m) Challis 24-38 - N Intermediate East Swan 0 90-215 Y N Y Low Elang 73-76 18 Intermediate Oliver 163 99 N N High Skua 9-51 7-17 Y Y Y Intermediate
TIMOR STRESS TENSOR TIMOR STRESS TENSOR Stress Magnitude (MPa) 25 50 75 100 0 1000 P p s hmin Magnitude s Hmax Magnitude 2000 s V Profiles (17 Wells) s V Depth Function ) m ( h t p e D 3000 4000
Timor Sea Structural Permeability Timor Sea Structural Permeability 000º Poles to planes southern hemisphere SHmax = 055ºN projection 45 ∆ P (MPa) 270º 090º 28 11 180º
Timor Sea Structural Permeability: Timor Sea Structural Permeability: Implications Implications • fault strike can vary as much as 60° and still maintain relatively low ∆ P values (high risk) for dips > 50° • ∆ P can alter by as much as 15 MPa with only a change of 10° in dip magnitude • confirms shear to be the most likely mode of failure
Challis Challis
East East
Elang Elang
Oliver Oliver
Skua Skua
Observed vs. Predicted Observed vs. Predicted
Evidence for Seal Breach in the Timor Sea Evidence for Seal Breach in the Timor Sea HC Residual Column Column Field HRDZ Sniffer ALF Integrity Heights Heights (m) (m) Challis 24-38 - N Intermediate East Swan 0 90-215 Y N Y Low Elang 73-76 18 Intermediate Oliver 163 99 N N High Skua 9-51 7-17 Y Y Y Intermediate
Calibration Results Calibration Results • Good correlation between observed fault trap integrity and FAST reactivation predictions • ∆ P < 10 MPa => Low integrity trap • 10 < ∆ P < 15 MPa => Moderate integrity trap • ∆ P > 15 MPa => High integrity trap
Hydraulic Seals and Hydrocarbon Retention Hydraulic Seals and Hydrocarbon Retention Capacity, Central North Sea Capacity, Central North Sea > σ 3 + T P p = σ 3 - P p R c ~ LOP-RFT R c σ 3 σ 2 σ 1 Gaarenstroom et al. (1993)
Tertiary Faults Skua 3D FAST Skua 3D FAST Mesozoic Faults
Comparison of 2D and 3D FAST Comparison of 2D and 3D FAST • Lowest ∆ P is similar between (approx. 12 MPa) • 2D FAST remains a useful tool for first-pass, regional assessments of fault reactivation
Discussion Discussion • reactivation causes breach • timing of reactivation • seal-breaching fractures vs. seismic faults • present-day vs. palaeo-stresses • variation in stress field • variation in failure envelope • sensitivity analysis • pore pressure/stress coupling
Shear Stress initial state σ h ’ σ v 0 Effective Normal Stress ( σ n -P p )
Shear Stress (MPa) 20 overpressure 10 ∆σ h ’ ∆σ v ’ 0 -5 5 15 25 35 45 55 σ h ’ σ v Effective Normal Stress ( σ n -P p )
Conclusions Conclusions • reactivation post-charge presents a risk of seal breach • juxtaposition and fault rock analyses suffice for ‘dead’ but not ‘live’ faults • tensile and/or shear failure impose dynamic limit to column height • like other geomechanically-based techniques, for risking reactivation, FAST requires knowledge of fault orientation and the in situ stress field • unlike other techniques, FAST incorporates the risk or tensile and/or shear failure into a single ∆ P parameter • unlike other techniques, FAST allows ‘real’ fault-rock failure envelopes to be incorporated • risk may vary on faults with constant strike, hence it is a 3D problem: not just use fault maps • FAST Map provides convenient method for analysing the problem in 3D for regional fault maps (from 2D seismic data) • methodology incorporated into FAPS/Traptester for use on faults mapped using 3D seismic data • calibration of FAST predictions is critical • sensitivity analysis of FAST predictions is critical
Acknowledgements Acknowledgements • Researchers and sponsors of APCRC Seals Consortium • Anthony Gartrell • Stress Group at NCPGG
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