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Contents Chapter 1 Introduction 1 1.1 Research background and significances 1 1.2 Unstable dynamic propagation behaviours of the multistage hydrofracturing fracture network 7 1.2.1 Deflection of fractures under the initiation sequence and perforation cluster spacing and well spacing 9 1.2.2 Disturbance of the stress field in the propagation process of multiple fractures 15 1.3 Mechanisms of induced deflection of fluid-driven fractures 16 1.3.1 Stress shadow effects between multiple fractures 17 1.3.2 Controlling factors of stress shadows 21 1.4 Numerical analysis of continuous stress field and discontinuous fracture 25 1.4.1 Continuum-discontinuum numerical methods and models 26 1.4.2 Simulation of stress-dependent unstable dynamic propagation of fractures 32 1.5 Challenges and perspectives 37 1.6 Conclusions 38 References 39 Chapter 2 Dual bilinear cohesive zone model for fluid-driven propagation of multiscale tensile and shear fractures 48 2.1 Introduction 48 2.2 Governing partial differential equations for hydrofracturing 52 2.2.1 Governing equations of solid deformation 53 2.2.2 Governing equations of fluid flow in fractured porous media 55 2.3 Dual bilinear cohesive zone model 56 2.4 Numerical discretization 58 2.4.1 Finite element discretization for solid 58 2.4.2 Finite volume discretization for fluid 59 2.5 Detection and separation of discrete elements 60 2.6 Global algorithm and procedure 62 2.7 Results and discussion 63 2.7.1 Verification of fracture propagation through analytical solutions in KGD and PKN models 63 2.7.2 Laboratory scales: dynamic propagation of small-size hydraulic fractures 67 2.7.3 Engineering scales: dynamic propagation of large-size hydraulic fractures 68 2.7.4 Distribution of tensile and shear fractures in hydrofracturing process 73 2.8 Conclusions 75 References 76 Chapter 3 Multi-thread parallel computation method for dynamic propagation of hydraulic fracture networks 80 3.1 Introduction 80 3.2 Governing partial differential equations and fracture criteria for hydrofracturing 83 3.3 Multi-thread parallel computation scheme for solid and fluid analysis 83 3.4 Global algorithm and procedure 84 3.5 Results and discussion 86 3.5.1 Example 1: Verification for multi-thread parallel computation solutions of hydraulic fracture propagation 86 3.5.2 Example 2: Multi-thread parallel computation efficiency for fluid-driven fracture propagation 90 3.5.3 Example 3: Parallel computation using multi-type elements and meshes 93 3.5.4 Example 4: Dynamic propagation behaviours of fractures under in-situ stresses and external fluid drive 96 3.6 Conclusions 99 References 100 Chapter 4 Heterogeneous continuum-discontinuum computation method for dynamic diversion and penetration of hydraulic fractures contacting multi-layers and granules 105 4.1 Introduction 105 4.2 Governing partial differential equations and fracture criteria in fractured porous media 109 4.3 Combined finite element-discrete element-finite volume method and algorithm for multi-materials 110 4.4 Numerical models of tight heterogeneous reservoirs with bedding and granules 112 4.5 Results and discussions of dynamic propagation behaviours of hydraulic fractures in the multilayered reservoir 118 4.5.1 A typical example implementation of fracture propagation and pore pressure in the heterogeneous tight reservoir with beddings 118 4.5.2 Influence of bedding deviation angle and geomaterial properties on hydraulic fracture propagation 120 4.5.3 Quantitative final length and propagation states of hydrofracturing networks in heterogeneous tight reservoirs with beddings 126 4.6 Results and discussions of dynamic propagation behaviours of hydraulic fractures in embedded multi-granule reservoir 127 4.6.1 A typical example implementation of fracture propagation and pore pressure in the heterogeneous tight reservoir with granules 127 4.6.2 Influence of granule distribution and geomaterial properties on hydraulic fracture 129 4.6.3 Quantitative final length and propagation states of hydrofracturing networks in heterogeneous tight reservoirs with granules 132 4.7 Conclusions 134 References 135 Chapter 5 Dynamic propagation and intersection of hydraulic fractures and pre-existing natural fractures involving the sensitivity factors 139 5.1 Introduction 139 5.2 Combined finite element-discrete element method for hydrofracturing in fractured reservoirs 142 5.2.1 Geomechanical equations in hydrofracturing and gas production 142 5.2.2 Leak-off of fracturing fluid 144 5.2.3 Discrete fracture network model 144 5.2.4 Numerical discretization 145 5.3 Numerical models of fractured reservoir embedded discrete fracture networks 146 5.3.2 Cases study for typical pre-existing natural fractures 147 5.4 Results and discussion 151 5.4.1 Sensitivity factors of pre-existing natural fractures 151 5.4.2 Quantitative length and volume of fracture networks 155 5.4.3 Gas production in enhanced permeability fractured reservoirs 160 5.5 Conclusions 165 References 166 Cha