Foundations of Rock Mechanics in Oil and Gas Engineering

Preface
Contents
1 Rock Mechanics and Petroleum Engineering
1.1 General Concepts
1.2 Inherent Complexity of Rock Mechanics
1.2.1 Failure Properties of Rocks
1.2.2 Size Effect
1.2.3 Tensile Strength
1.2.4 Impact of Groundwater
1.2.5 Weathering
1.2.6 Rock Outside Loading
1.3 Rock Mechanics Problems in Oil and Gas Engineering
1.4 History of the Development of Rock Mechanics
References
2 Stress and Strain
2.1 Stress
2.1.1 Stress Vector
2.1.2 Stress Tensor
2.1.3 Stress Equation for Inclined Plane
2.1.4 Stress Coordinate Transformation
2.1.5 Principal Stresses and Principal Directions
2.1.6 Maximum Shear Stress
2.1.7 Stress Mohr Circle
2.1.8 Deviatoric Stress
2.1.9 Equilibrium Differential Equations
2.2 Strain
2.2.1 The Concepts of Deformation and Strain
2.2.2 Geometric Equations
2.2.3 State of Strain
References
3 Rock Composition and Physical Properties
3.1 Origin of Rock
3.2 Effect of Rock Structure on Strength
3.2.1 The Influence of Rock Composition on Rock Strength
3.2.2 Influence of the Structure and Tectonics of the Rock on Strength
3.3 Basic Physical Properties of Rocks
3.3.1 Bulk Density of Rocks
3.3.2 Porosity of the Rock
3.3.3 Permeability of the Rock
3.3.4 Water Content of the Rock
3.3.5 Particle Size Composition and Specific Surface Area of Rocks
3.3.6 Acoustic Properties of Rocks
References
4 Strength and Deformation Characteristics of Rocks
4.1 Mechanical Properties of Rocks at Ambient Temperature and Pressure
4.2 Effect of Confining Pressure and Intermediate Principal Stress on Mechanical Properties of Rocks
4.3 Effect of Temperature on Mechanical Properties of Rocks
4.4 Effect of Pore Pressure on Mechanical Properties of Rocks
4.5 Effect of Strain Rate on Mechanical Properties of Rocks
References
5 Characterization and Indoor Determination of the Strength of Rocks
5.1 Types of Tock Damage and Destruction
5.1.1 Preparation of Rock Samples
5.1.2 Types of Rock Damage
5.2 Compressive Strength of Rocks and Its Influencing Factors
5.2.1 Compressive Strength of Rocks
5.2.2 The Influencing Factors of Compressive Strength
5.3 Tensile Strength of Rocks and Its Influencing Factors
5.3.1 Direct Stretching Method
5.3.2 Indirect Stretching Method
5.4 Shear Strength of Rocks and Its Influencing Factors
5.4.1 Direct Shear Experiment
5.4.2 Rock Triaxial Experiments
5.4.3 Rock Shear Experiments at the Mine Site
References
6 Rock Strength Failure Criterion
6.1 Coulomb Failure Criterion
6.2 Mohr Failure Criterion
6.3 Failure Criterion for Rock Formations with Weak Planes
6.4 Griffith Criterion
6.4.1 Griffith Criterion Derivation
6.4.2 Modified Griffith Criterion
References
7 In-Situ Stress States
7.1 Description of In-Situ Stress State
7.2 Factors Affecting the State of In Situ Stress
7.2.1 Surface Shape
7.2.2 Residual Stresses
7.2.3 Envelope
7.2.4 Tectonic Stress
7.2.5 Fissure Groups and Discontinuity Surfaces
7.3 Method for Determining In-Situ Stress
7.3.1 General Approach
7.3.2 Three Directional Stress Gauges
7.3.3 Pressure Pillow Measurement
7.3.4 Hydraulic Fracturing
7.3.5 Differential Strain Method
7.4 Basic Laws of In-Situ Stress Distribution
7.4.1 In-Situ Stress Is a Relatively Stable Unsteady Stress Field
7.4.2 Measured Vertical Stress Is Essentially Equal to the Overlying Rock Pressure
7.4.3 The Horizontal Stress Distribution Is More Complex
7.4.4 Performance Characteristics of High Stress Areas
References
8 Mechanics of Wellbore Stability
8.1 Causes and Hazards of Wellbore Instability
8.1.1 Causes of Wellbore Instability and Research Methods
8.1.2 Hazards of Unstable Well Walls
8.2 Stress Distribution of Confining Rock of Vertical Well
8.2.1 Stress Distribution Model of Vertical Well
8.2.2 The Stress Distribution in Vertical Wellbore Surrounding Rock
8.3 Collapse and Rupture of Well Walls
8.3.1 Mechanisms of Well Wall Instability
8.3.2 Judgement of Wellbore Collapse
8.3.3 Judgement of Wellbore Fracture
8.3.4 Factors Influencing Wellbore Stability
8.4 Model for Predicting Formation Fracture Pressure
8.4.1 Leakage Test
8.4.2 Model for Predicting Formation Fracture Pressure
8.5 Example of Borehole Stability Calculation
References
9 Mechanics of Hydraulic Fracturing
9.1 The Role of Fracturing
9.1.1 Flow Characteristics of Fractured Wells
9.1.2 Optimal Design Process for Hydraulic Fracturing
9.1.3 Introduction to Fracturing Fluids
9.2 Fracture Stress Field Analysis
9.2.1 Solution of Internally Compressed Linear Fractures
9.2.2 Constant Pressure Distribution in the Seam
9.2.3 The Pressure Distribution in the Fracture as a Polynomial
9.2.4 Smooth Closure of Fractures
9.2.5 Shape of Fractures and Net Pressure Concept Under In-Situ Stress Conditions
9.2.6 Circular Cracks
9.3 Law of Conservation of Matter
9.3.1 The Law of Conservation of Matter
9.3.2 Fluid Filtration Loss and Initial Filtration Loss
9.3.3 Carter Equation
9.3.4 Approximation of the Power-Law Growth of the Fracture Surface Area with Treatment Time
9.3.5 Numerical Methods for Equilibrium Equations of Matter
9.4 PKN Model and KGD Model
9.4.1 Reasonableness of the Plane Strain Assumption
9.4.2 Filter-Free 2D Model
9.4.3 2D Model When Considering Filtering Loss
9.5 Factors Influencing Fracture Extension
9.5.1 Fracture Extensions in Vertical Wells
9.5.2 The Fracture Extension in Horizontal Well
9.5.3 Multi-layered Fracture Profiles
References
10 Mechanics of Oil Well Sand Production
10.1 Basic Processes and Hazards of Oil Well Sanding
10.1.1 Basic Process of Sand Emergence from Oil Wells
10.1.2 Factors Influencing Sand Emergence from Oil Wells
10.1.3 Hazards of Sand Emergence and Prevention
10.2 Analysis of the Sand Production Mechanism
10.2.1 Differential Production Pressure Required for Fluid Flow
10.2.2 Stress in the Near-Wellbore
10.2.3 Mechanisms of Stratigraphic Damage
10.3 Analysis of Sand Emergence Under Different Completion Methods
10.3.1 Critical Sanding Conditions for Open-Hole Completions
10.3.2 Critical Sand-Out Conditions for Perforation Completions
10.3.3 Sand Arch and Its Stability Model
10.3.4 Effect of Pressure Depletion on Reservoir Critical Production Pressure Differential
10.4 Experimental Study of the Sanding Mechanism
10.4.1 Permeability Force and Critical Pressure Gradients
10.4.2 Sand Arch Stability Experiments
10.5 Predicting Models for Oil Well Sand Production
10.5.1 Single Parameter Model
10.5.2 Multi-parameter Models
10.5.3 Engineering Forecasting Method
References
Glossary