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EARS5136 slide 1
FAULT SEAL ANALYSIS:Mapping & modelling
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EARS5136 slide 2
Hydrocarbon field structure
Compartments
How to produce field ?
1 km
Depth ~2.5km
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EARS5136 slide 3
Predict flow patterns and communication
Fault compartments in the Sleipner field, Norwegian North Sea
Different oil-water contacts
Ottesen Ellevset et al. (1998)
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EARS5136 slide 4
Seal Mapping - Complexities Horizon / fault zone resolution (thin sand problem)
Lack of reflectors for mapping
Stratigraphic architecture / sediment pinchout
Erosional truncation
Intersecting faults
Sub-seismic seal elements
Multiple faulting events (reactivation) and impact on seal distribution and properties
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EARS5136 slide 5
Fault Seal WorkflowDefine geometry of fault array
Test models against hydrocarbon contact levels if known
Assess sealing mechanisms and fault rock properties
Evaluate juxtapositions and seal distributions
Map seal distributions on fault planes which might form compartment boundaries
Establish sub-seismic fault density and fault zone structure
Model reservoir flow and impact of faults on drainage patternsModel reservoir flow and impact of faults on drainage patterns
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EARS5136 slide 6
Allan diagramsFootwall template >
< Hangingwalltemplate
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EARS5136 slide 7
Allan diagrams
Areas where sands not in contact are juxtaposition seals
Migration possible by stair-stepping between hangingwall & footwall across sand-sand windows
Use fault seal algorithms to predict behaviour of juxtaposed sands
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EARS5136 slide 8
Allan Diagrams: Bed-Fault Intersections
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EARS5136 slide 9
Seismic data in juxtaposition analysis
Example showing modelled fault surface with stratigraphicjuxtapositions
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EARS5136 slide 10
Do we assess fault juxtapositions correctly?
Allan Maps Accuracy; Horizon uncertainty: +20m to -20m Fault Uncertainty: ~100m
Assume single fault, not complex damage zone
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EARS5136 slide 11
Snappinghorizons to faults
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EARS5136 slide 12
Impact of Seismic Data Interpretation on Resolution and Quality of Allan Diagrams
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EARS5136 slide 13
Impact of Seismic Data Interpretation on Resolution and Quality of Allan Diagrams
uncertainty
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EARS5136 slide 14
Impact of branch-lines from intersecting faults
uncertainty
Branch-lines
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EARS5136 slide 15
Complex Fault Plane Mapping
1200
1400
1600
1800
1 kmIntra F Fault Juxtapositions
S
Depth (m)
N
Fig 6-41
1340m
UPPER RE / LOWER RE
F HW
BCU FW
BCU HW
BCU FW
BCU HW
F FW
F FW
INTRA RE
FW
F2
F6
TOP FW
F HW
TOP H
W
TOP HW
TOP
HW
TOP RE HW
TOP RE HW
INTRA
RE FW
INTRA RE
FW
INTRA RE HW
INTRA
RE F
W
INT
RAR
EHW
INTRA RE HW
INTRA RE FWUpper re / Lower re
Upper re / Upper re
Fangst in HW / Lower re in FW
Fangst in HW / Upper re in FW
Fangst / Fangst
Upper Jurassic in HW
BCU in HW
Erosional Contact
INTRA RE HW
TOP RE HW
TOP RE FW
F HW
F FW
BCU HW
BCU FW
Intra-formational erosion / pinchout
BCU in HW
U Jur in HW
Fangst / Fangst
Fangst HW / Up Are FW
Fangst HW / Lr Are FW
Up Are HW / Up Are FW
Up Are / Lr Are FW
Erosional contact
Erosion and30m Seismic Resolution
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EARS5136 slide 16
Seismic horizon juxtaposition
Four seismically mapped horizons displayed on strike view of fault.
example
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EARS5136 slide 17
Fault throw
Four seismically mapped horizons displayed on strike view of fault.
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EARS5136 slide 18
Stratigraphic juxtaposition: relative reservoir quality I
Reservoir quality
seal
Reservoir against reservoir
Relative reservoir quality index based on a scale normalized to lithological property seals have larger numbers.
The larger index juxtaposed across the fault controls the seal and is displayed.
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EARS5136 slide 19
Stratigraphic juxtaposition: relative reservoir quality II
Relative reservoir quality index based on a high, med or low determination
The juxtaposition combination of the reservoirs on either side of the fault are color-coded as shown.
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EARS5136 slide 20
Shale Gouge Ratio
Juxtaposed reservoirs on either side of the fault are color-coded for SGR as shown.
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EARS5136 slide 21
Seal Comparison
Reservoir qualityseal
High risk windows for fault seal juxtaposition may be sealed by shale gouge mechanism.
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EARS5136 slide 22
Juxtaposition diagrams
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EARS5136 slide 23
Juxtaposition Diagrams Rapid modelling of seal distributions possible Seismic mapping input not required initially Possible to analyse reverse faults, growth faults and variable
FW/HW stratigraphy, but more difficult
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EARS5136 slide 24
Communication Map
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EARS5136 slide 25
Fault Throw Distributions
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EARS5136 slide 26
Fault Rock Type Map
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EARS5136 slide 27
Seismic Throw: Hangingwall Communication
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EARS5136 slide 28
Seal mapping& vertical continuity
Separate Risk for :
a) Faults linked to Zechsteinb) Faults not linked
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EARS5136 slide 29
Overall Seal Workflow
(1) Create depth structure map
(2) Map fault activity and linkage
(3) Evaluate reactivation risk and top seal
(4) Undertake juxtaposition / seal mapping for faults trapping unreactivated prospects
(5) Evaluate impact of seismic resolution, depth conversion etc.
(6) Re-integrate with larger-scale tectonic / fluid flow evolution
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EARS5136 slide 30
Putting it all together ..the reservoir model
Porosity modelGullfaks field
Geocellular models of reservoir rock properties..but what about the faults?
Models should attempt to capture fault properties but upscaling can be difficult
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EARS5136 slide 31
Fault Throw
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EARS5136 slide 32
Fault rock thickness
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EARS5136 slide 33
Stratigraphic juxtaposition
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EARS5136 slide 34
Fault rock permeability
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EARS5136 slide 35
Sand-Sand windows
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EARS5136 slide 36
Basis of fault modeling in reservoir simulations Reservoir models of entire field (full-field) or part
of a field (sector)
Faults considered as single plane
Modelled flow path as part of cross-cell flow calculation
Use modifiers of transmissibility between cells
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EARS5136 slide 37
Manzocchi et al. (2002)
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EARS5136 slide 38
Fault zone transmissibility
Fault Rock Thickness
Fault Rock Permeability
Transmissibility(Perm x Fault rock thickness)
Hydraulic Resistance(Fault rock thickness / Perm)
Matrix PropertiesCell Size
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EARS5136 slide 39
Only Cross-fault cells used :- No along fault flow
considered- No Threshold Capillary Pressure considered
Separate cells for faultsallows along fault flow evaluation
Transmissibility multipliersand flow modeling
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EARS5136 slide 40
Fault zone hydraulic resistance
Flow across a fault in reservoir models follows Darcy flow:
The rate for linear flow is:
q = (k/L) (A/) (1 - 2)
For a given cross-sectional area, A, across the fault and a constant pressure gradient and fluid viscosity, the flow rate is dependent on the fault zone hydraulic resistance or, (k/L), where L is the fault rock thickness.
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EARS5136 slide 41
Transmissibility no fault Fault zone properties are introduced into reservoir
models as transmissibility multipliers.
Average permeability for flow between adjoining cells with no fault is:
k undeformed = L / [(0.5L1/ k1) + (0.5L2/ k2)]
And transmissibility (T trans) is K undeformed /L
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EARS5136 slide 42
Fault transmissibility with fault
Average permeability for flow between adjoining cells with a fault is:
k faulted = L / [0.5 (L1 - Lf) / k1] + [0.5 (L2 - Lf) / k2] + [Lf / kf]
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EARS5136 slide 43
Transmissibility multiplier - T
Transmissibility with a fault is altered by transmissibility multiplier, T
Ttrans = T (kundeformed/L) for no fault T=1 and for a completely sealing fault T=0
The transmissibility multiplier is the ratio of the faulted permeability to the undeformed permeability that is:
T = kfaulted/kundeformed
This is the key relationship introduced into reservoir models.
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EARS5136 slide 44
Transmissibility multiplier - T
The transmissibility multiplier is:
T = kfaulted/kundeformedwhere,
k faulted = L / [0.5 (L1 - Lf) / k1] + [0.5 (L2 - Lf) / k2] + [Lf / kf]
is a function of the fault permeability, kf and fault rock thickness, Lf.
The fault rock thickness is associated with the fault throw, Lf.
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EARS5136 slide 45
Fault rock thicknessFault rock thickness scales with fault displacement
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EARS5136 slide 46
Manzocchi et al. (2002)
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EARS5136 slide 47
Fault rock permeability vs. clay content
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EARS5136 slide 48
Fault Zone Flow
Transmissibility depends on cell size
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EARS5136 slide 49
Fault Zone Flow
Transmissibility depends on cell size
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EARS5136 slide 50
Fault Rock Prediction: Heidrun field
Knai & Knipe (1998)
FAULT SEAL ANALYSIS: Mapping & modellingSeal Mapping - ComplexitiesFault Seal WorkflowAllan diagramsAllan Diagrams: Bed-Fault IntersectionsSeismic data in juxtaposition analysisDo we assess fault juxtapositions correctly? Snapping horizons to faultsImpact of Seismic Data Interpretation on Resolution and Quality of Allan DiagramsComplex Fault Plane MappingJuxtaposition DiagramsCommunication Map Fault Throw DistributionsFault Rock Type MapSeismic Throw: Hangingwall CommunicationSeal mapping& vertical continuityOverall Seal WorkflowFault ThrowFault rock thicknessStratigraphic juxtapositionFault rock permeabilitySand-Sand windowsBasis of fault modeling in reservoir simulationsFault zone transmissibilityTransmissibility multipliersand flow modelingFault rock thicknessFault rock permeability vs. clay contentFault Zone Flow Fault Zone FlowFault Rock Prediction: Heidrun field
