structural analysis of fractured hydrocarbon reservoirs: role of rock rheology seth busetti...
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Structural Analysis of Fractured Hydrocarbon Reservoirs:
Role of Rock Rheology
Seth BusettiUniversity of Oklahoma
November 2008
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Understanding Rock Deformation
Sanders et al., 2004
Lacazette, 2000
Maerten and Maerten, 2006
Analog Experiments
Kinematic Restoration / Forward Modeling
Linear Elastic Modeling
Mechanical Simulation
Relatively SimpleUses only Geometry
Simple ComputationValid for Small Strain
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Deformation of Rock LayersFour main stages of rock deformation
Mt. Scott Granite
(Katz and Reches, 2004)
Crack/pore closure
Linear Elastic Stage
Damage byMicrocracking [Strain Hardening]
Extensive Damage,Crack Coalescence
Macroscopic Fracturing
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Mechanical Simulations of StructuresPhysical Observations Mathematical ExpressionStructure
LayeringFoldsFaults/Fractures
Geologic FeaturesRamps, pins, blocksLayer Friction
Stress ConditionsTectonic StressLocal Stress
Rock Mechanics PropertiesElasticityPlasticityFailurePorosity/Permeability
Numerical MethodGeometry
Discretization (nodes/elements)Discontinuities
Boundary ConditionsDegrees of FreedomPenalty Contact
Loading ConditionsSurface PressurePoint/surface Loads
*Rock [Material] Rheology Material Model Parameters σ-ε curve
u1x
u1y
u2x
u2y
u3x
u3y
u4x
u4y
[Ke]
[K]{u}+[M]{a}+[C]{v} = {f}
{f}
Ellenberger LimestoneBarnett Siliceous ShaleBarnett MudstoneBarnett Calcareous MudstoneBerea SandstoneIndiana Limestone
Preliminary Material Modeling: Calibration / Benchmark Testing
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Deformation of Rock Layer: 4-Point BeamBerea Sandstone Rheology: Elastic-Plastic with Damage
0 0.001 0.002 0.0030.0E+00
2.0E+06
4.0E+06
6.0E+06
8.0E+06
1.0E+07
1.2E+07
1.4E+07
1.6E+07
1.8E+07Differential σ vs. Axial ε
Strain
Diffe
renti
al S
tres
s
Onset of Damage [Plasticity]
Stiffness Degradation
Failure [Fracture]
Piston Down
10 MPa Confining Pressure [Triaxial]
Beam
Loading Piston
Load CellConfining Pressure
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Deformation of Rock Layer: 4-Point BeamBerea Sandstone Rheology: Elastic-Plastic with Damage
0.00E+00 1.00E-02 2.00E-02 3.00E-02 4.00E-02 5.00E-02 6.00E-02 7.00E-02 8.00E-020.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20 Fracturing Stage
Coalescence
Microcracking Stage
Elastic Stage
Damage Before Failure
Distance from Center (m)
d2y/
dx2
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Large-Scale Deformation ApplicationMohr-Coulomb Rheology
20,000 m
10,000 m
Open Questions:Damaged Shear Zones vs. Fault Planes?Mechanisms for Fault Rotation?Role of Footwall Deformation?
Chimney and Kluth, 2002
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Summary
Rheology strongly effects rock deformation
Deformed rocks contain pervasive damage
Damaged layers frequently behave plastically
A Mechanical approach may be necessary to understand many reservoirs, especially where fractures and faults are prevalent
Numerical (i.e., finite element) techniques are a powerful tool for analyzing complex reservoir structures using realistic mechanics