FAST: A New Approach to Risking isking FAST: A New Approach to R - - PowerPoint PPT Presentation

FAST: A New Approach to R FAST: A New Approach to Risking isking Fault Reactivation and Related Seal Breach Fault Reactivation and Related Seal Breach

Scott Mildren Scott Mildren & Richard Hillis & Richard Hillis APCRC, NCPGG, APCRC, NCPGG, The University of Adelaide, Australia The University of Adelaide, Australia AAPG AAPG Hedberg Hedberg Research Research Confere Conferenc nce, e, Barossa Valley, South Australia, 1 Barossa Valley, South Australia, 1-

• 5 December 2002

5 December 2002

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 Dynamic Seal Breach: Timor Sea HRDZs HRDZs

O’Brien & Woods (1995)

Dynamic Seal Breach: Timor Sea Dynamic Seal Breach: Timor Sea HRDZs HRDZs

O’Brien & Woods (1995)

Hydrocarbon Seals Hydrocarbon Seals

Seals Caprock Fault Other Fracture (Hydraulic) Membrane Sealing Faults Juxtaposition Hydrodynamic after Watts (1987)

Hydrocarbon Seals Hydrocarbon Seals

Seals Caprock Fault Other Fracture Membrane Sealing Faults Juxtaposition Hydrodynamic Fracture/React

Dead faults Live faults

Jones et al. (2000)

Dead Faults Dead Faults

• r Live Faults?
• r Live Faults?

Fault Fault-

• Valve Model

Valve Model Fault reactivation post-charge leads to breaching of the seal

Sibson (1992)

Effectiveness of Fracture Permeability Effectiveness of Fracture Permeability

30 cm 30 cm Fracture Aperture 0.25 mm 30 cm

1 3 5 1 m D 1 mD Matrix Permeability 1 mD

• Ave. Permeability 1 mD

Matrix Permeability 1 mD

• Ave. Permeability 13 510 mD

Failure Modes Failure Modes

Rock Failure Rock Failure

Structural Permeability Structural Permeability

Failure Mode Criterion Condition Tensile (hydraulic) Pp=σ3+T (σ1-σ3)<4T Tensile/shear Pp=σn+(4T2-τ2)/4T 4T<(σ1-σ3)<6T Shear Pp=σn+(Ci-τ)/µi (σ1-σ3)>6T Shear reactivation Pp=σn+(Cs-τ)/µs

• Stylolite

? fine-grained matrix

Sibson (1996)

Rock Failure Rock Failure

Structural Permeability Structural Permeability

Sibson (1996)

Structural Permeability: Structural Permeability: Mesoscale Mesoscale

Cosgrove (1995)

Structural Permeability Structural Permeability

Ferrill & Morris (2002)

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

Pp > σ3 + T Rc = σ3 - Pp ~ LOP-RFT

σ1 σ2 σ3 Rc

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 −σ3 −σn σ1 σ1 Td =

Shear Stress

σ1 σ2 σ3 σn

Normal Stress

Ferrill et al. (1999)

Slip Tendency Slip Tendency

Slip tendency is defined as the ratio of shear stress to normal stress σs σn Ts =

Shear Stress

σ1 σ2 σ3 σs σn

Normal 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)

FAST Map

In Situ Stress Tensor Structural Permeability Developmen Segment Fault Centreline With Dip Fault Polygons Mohr's Circle Failure Envelop

FAST I FAST I

FAST ISS SP SF CD FP MC FE

σHmax = 82 MPa σhmin

= 46 MPa

σv

= 64 MPa Po = 28 MPa

σH orient. = 156°N

FAST II FAST II

Cataclasites in Pretty Hill Formation, Banyula-1, Otway Basin

Shear Stress (MPa)

τ = 5.4 + 0.78σn' 20 40 60

C µ

τ = C + µσn'

FAST ISS SP SF CD FP MC FE

80 60 40 20

Effective Normal Stress (MPa)

FAST III FAST III

σH’ σh’ σv’

FAST ISS SP SF CD FP MC FE

FAST IV FAST IV

1.0 0.8 0.6 0.4 0.2 0.0 0.9 0.7 0.5 0.3 0.1

RP RP

σHmax = 156οN

30 60 90 120 150 180 210 300 270 330

σHmax = 82 MPa σhmin

= 46 MPa

σv

= 64 MPa Po = 28 MPa

σH orient. = 156°N

240 FAST ISS SP SF CD FP MC FE

FAST V FAST V Acquired from seismic Collapse fault polygons to centreline

FAST ISS SP SF CD FP MC FE

FAST ISS SP SF CD FP MC FE

FAST VI FAST VI

1.0 0.0 0.5

Evidence for Seal Breach in the Timor Sea Evidence for Seal Breach in the Timor Sea

Field HC Column Heights (m) Residual Column Heights (m) HRDZ Sniffer ALF Integrity Challis 24-38

• N

Intermediate East Swan 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)

1000 2000 3000 4000 25 50 75 100

P

p

shmin Magnitude sHmaxMagnitude sVProfiles (17 Wells) sVDepth Function

Timor Sea Structural Permeability Timor Sea Structural Permeability

000º 090º 180º 270º

Poles to planes southern hemisphere projection SHmax = 055ºN

45

∆P (MPa)

28 11

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

Intermediate Y Y Y 7-17 9-51 Skua High N N 99 163 Oliver Intermediate 18 73-76 Elang Low Y N Y 90-215 East Swan Intermediate N

• 24-38

Challis Integrity ALF Sniffer HRDZ Residual Column Heights (m) HC Column Heights (m) Field

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

Pp > σ3 + T Rc = σ3 - Pp ~ LOP-RFT

σ1 σ2 σ3 Rc

Gaarenstroom et al. (1993)

Skua 3D FAST Skua 3D FAST

Tertiary Faults 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

initial state Shear Stress Effective Normal Stress (σn-Pp) σh’ σv

• verpressure

∆σv’ ∆σh’ 10 20

• 5

5 15 25 35 45 55

Effective Normal Stress (σn-Pp) σh’ σv Shear Stress (MPa)

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