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Introduction to Energy Geomechanics
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Introduction to Energy Geomechanics
Contents
1. Introduction
1.1 Structural Geology
1.2 Geomechanics in the Energy Industry
1.2.1 Drilling and Wellbore Stability
1.2.2 Wellbore Completion
1.2.3 Reservoir Geomechanics
1.2.4 Carbon and Hydrogen Geological Storage
1.2.5 Geothermal Energy
1.3 Problems
1.4 Further Reading and References
2. Subsurface Stresses and Pore Pressure
2.1 Lithostatic gradient
2.1.1 Stress concept and equilibrium 1D
2.1.2 Rock vertical stress gradient
2.2 Non-hydrostatic pore pressure
2.2.1 Mechanisms of overpressure
2.2.2 Disequilibrium compaction and excess pore pressure
2.2.3 Reservoir depletion
2.3 Horizontal stresses
2.3.1 Background
2.3.2 Geological indicators
2.3.3 In-situ measurement
2.3.4 Stress Regimes
2.3.5 Ideal orientation of open-mode fractures
2.4 Problems
2.5 Further reading and references
3. Fundamentals of Solid Continuum Mechanics
3.1 Stress tensor
3.1.1 Cauchy's equations of stress equilibrium
3.1.2 Application of Cauchy's equations for total vertical stress calculation
3.1.3 Continuum mechanics solution of an arbitrary problem
3.2 Kinematic equations: displacements and strains
3.3 Constitutive equation: stress-strain relationships
3.3.1 Linear isotropic elasticity
3.3.2 The isotropic solid in Voigt notation
3.3.3 Effective stress and elasticity
3.3.4 Calculation of horizontal stress according to linear elasticity
3.3.5 Calculation of reservoir compressibility with linear elasticity
3.3.6 Generalized linear elasticity problem
3.4 Elastic anisotropy
3.5 Permanent deformation: Elasto-plasticity
3.6 Time-dependent deformation: Visco-elasticity
3.7 Multiphysics problems
3.7.1 Poro-elasticity
3.7.2 Thermo-elasticity
3.8 Problems
3.9 Further reading and references
4. Rock Yield and Failure
4.1 Preliminary concepts
4.1.1 Microstructure of geologic materials
4.1.2 Length scales v.s. process zone size
4.1.3 Overview of types of rock failure
4.2 Tensile failure
4.2.1 Direct tension
4.2.2 The Brazilian test
4.3 Shear failure
4.3.1 Frictional Strength
4.3.2 Unconfined compression strength
4.3.3 Confined strength: the triaxial test
4.3.4 Triaxial tests of fluid saturated rocks and sediments
4.4 Compression failure: Pore collapse
4.5 Yield/failure locus
4.6 Strength anisotropy
4.7 Deformation beyond the elastic limit
4.8 Rock damage and failure revisited
4.9 Problems
4.10 Further reading and references
5. Stresses on Faults and Fractures
5.1 Introduction
5.2 Mapping of faults and fractures
5.2.1 Orientation of planes with respect to the geographical coordinate system
5.2.2 Stereonets for plotting fault orientation
5.2.3 Faults in geological maps
5.3 Frictional strength of faults and fault types
5.3.1 Fault strength
5.3.2 Normal faults
5.3.3 Thrust and reverse faults
5.3.4 Strike-slip faults
5.3.5 Stress and faulting regimes
5.3.6 Ideal orientation of faults
5.4 Determination of normal and shear stresses on the fault plane
5.4.1 Mohr's circle method
5.4.2 Tensor method
5.5 Applications
5.5.1 Critically stressed fractures and permeability
5.5.2 Determination of horizontal stresses assuming limit equilibrium
5.5.3 Determination of stress regime and horizontal stress direction from fault orientation
5.5.4 Fault reactivation
5.6 Problems
5.7 Further reading and references
6. Wellbore Stability
6.1 The wellbore environment
6.2 Kirsch solution for stresses around a cylindrical cavity
6.2.1 Cylindrical coordinate system
6.2.2 Kirsch solution components
6.2.3 Complete Kirsch solution
6.3 Shear failure and wellbore breakouts
6.3.1 Breakout angle determination
6.3.2 Breakout measurement
6.3.3 Maximum horizontal stress determination from breakout angle
6.4 Tensile fractures and wellbore breakdown
6.4.1 Identification of tensile fractures in wellbores
6.5 The mud window
6.6 Mechanical stability of deviated wellbores
6.6.1 Wellbore orientation
6.6.2 Calculation of stresses on deviated wellbores
6.6.3 Breakout analysis for deviated wellbores
6.6.4 Tensile fractures analysis for deviated wellbores
6.7 Thermal, chemical, and leak-off effects on wellbore stability
6.7.1 Thermal effects
6.7.2 Chemo-electrical effects
6.7.3 Leak-off effects
6.8 Strength anisotropy
6.9 Problems
6.10 Further reading and references
7. Hydraulic fracturing
7.1 Fluid-driven fractures in nature
7.2 Hydraulic fractures in well testing
7.2.1 Leak-off test
7.2.2 Diagnostic fracture initiation test (DFIT)
7.2.3 Step-rate test
7.3 Hydraulic fracture design: Single fracture completion
7.3.1 Improvement of reservoir access and wellbore-reservoir surface area
7.3.2 The coupled fluid-driven fracture propagation problem
7.3.3 Fracture design: Single planar models
7.3.4 Stress logs and implications on hydraulic fracture height
7.4 Multistage hydraulic fracturing
7.4.1 Increased surface area with multiple fractures
7.4.2 Fracture interference and fracture hit
7.4.3 Fracture reactivation and microseismicity
7.4.4 Multiple strands in hydraulic fracture propagation
7.5 Practical aspects of hydraulic fracturing
7.6 Problems
7.7 Suggested Reading
8. Reservoir depletion and injection
8.1 Changes of stress in the reservoir rock
8.1.1 Rock compressibility and permeability
8.1.2 Linear poroelasticity solution
8.2 Changes of stress in the vicinity of the reservoir
8.3 Fluid injection
8.4 Fault stability
8.5 Suggested Reading