Cover	1
	Title Page	5
	Copyright	6
	Contents	9
	Foreword	13
	Preface	15
	Acknowledgements	17
	Introduction	19
	Part 1 Understanding Natural Fractures: Fracture Types, Dimensions, and Origin	21
	1.1 Introduction	21
	1.2 Nomenclature and Fracture?Classification Systems	21
	1.2.1 Introduction	21
	1.2.2 Other Classification Systems	23
	1.2.3 Classifications for Fractures in Outcrops and Cores	24
	1.2.4 Expulsion Fractures and Natural Hydraulic Fractures	25
	1.2.5 Other Fracture Terminology	25
	1.2.6 Sets, Systems, Domains, and Systematic Fractures	27
	1.3 Fracture Characteristics and Dimensions	28
	1.3.1 Introduction	28
	1.3.2 Fracture Distribution Patterns	28
	1.3.3 Fractography	30
	1.3.4 Fracture Dip Angles	33
	1.3.5 Fracture Distributions	33
	1.3.6 Fracture Heights and Terminations	36
	1.3.7 Fracture Lengths	38
	1.3.8 Fracture Widths, Apertures, and Mineralization	39
	1.3.9 Fracture Spacing	42
	1.3.10 Fracture Strike	47
	1.3.10.1 Fracture Orientations Relative to the In Situ Stresses	48
	1.3.11 Discussion	48
	1.4 The Mechanics of Fracturing Rock in Extension and Shear	49
	1.4.1 Introduction	49
	1.4.2 Origins of Geologic Stress Systems	51
	1.4.2.1 Stresses in a Tectonically Quiescent Basin	51
	1.4.2.2 Other Potential Sources of Horizontally Isotropic Stress	52
	1.4.2.3 Stresses in a Tectonically Active Basin	52
	1.4.3 Rock Susceptibility to Fracture: Basic Concepts	55
	1.4.3.1 Introduction	55
	1.4.3.2 Intrinsic Controls on Fracture Susceptibility	58
	1.4.3.3 Extrinsic Controls on Fracture Susceptibility	59
	1.4.3.4 How Rock Breaks: Grain?Scale Cracking, Yield, and Failure	61
	1.4.3.5 Extrapolation to the Subsurface	63
	1.4.4 Interplay Between Developing Fractures and the In Situ Stresses	64
	1.4.5 The Importance of Pore Pressure	65
	1.4.5.1 Introduction	65
	1.4.5.2 The Relationship between Pore Pressure and Stress	65
	1.4.5.3 Biot's Coefficient	67
	1.4.5.4 Mohr Diagrams and Pore Pressure	67
	1.4.5.5 Pore Pressure Makes Rock Weak and Brittle	67
	1.4.5.6 Sources of Pore Pressure	70
	1.4.5.7 Alternate Theories	71
	1.4.6 Summary	72
	1.5 Other Fracture Types	73
	1.5.1 Introduction	73
	1.5.2 Deformation?Band Shear Fractures, Compaction Bands, and Dilation Bands	73
	1.5.2.1 General Characteristics	73
	1.5.2.2 Dimensions and Distributions	73
	1.5.2.3 Origin	74
	1.5.3 Faults and Fractures	75
	1.5.4 Microfractures	76
	1.5.5 Stylolites and Associated Extension Fractures	79
	1.5.6 Bed?Parallel Shear Fractures	79
	1.5.7 Beef?Filled Fractures	82
	1.5.8 Ptygmatically Folded Fractures	83
	1.5.9 Alteration of Fracture Systems by Dissolution	84
	Appendix 1.A The Relationship Between Pore Pressure and the In Situ Effective Stresses	86
	Introduction	86
	Vertical Stress	87
	Horizontal Stress	87
	Effective Vertical Stress	87
	Effective Horizontal Stress	88
	Stress Differential	88
	Part 2 Measuring and Analyzing Fractures in Reservoirs	91
	2.1 Introduction	91
	2.1.1 Reasons to Take Core	92
	2.1.2 Analyses	93
	2.1.3 Fracture Data Sources	93
	2.1.4 Quantitative vs. Semi?Quantitative Data	93
	2.1.5 Timing of a Fracture Study	93
	2.1.6 Need for Experience	94
	2.1.7 Other Data Sources	94
	2.2 Planning a Core Program for Fracture Analysis	94
	2.2.1 Introduction	94
	2.2.2 Core Diameter and Length	94
	2.2.3 Substituting Sidewall Core Samples	94
	2.2.4 Orienting a Core	94
	2.2.5 Drilling Parameters	95
	2.2.6 Trip Time for Core Recovery	95
	2.2.7 Collecting Data on Site	95
	2.2.8 Running an Image Log	96
	2.2.9 Back?to?Back Cores	96
	2.2.10 On?Site Processing	96
	2.2.11 CT Scans	97
	2.2.12 Removing Core from the Barrel	97
	2.2.13 Core?Jam Prevention Measures	97
	2.2.14 Maximizing and Documenting Core Continuity	97
	2.2.15 Slabbing Protocol	97
	2.2.16 Scheduling Fracture Logging and other Core Processes	98
	2.3 Logging Core for Fractures	98
	2.3.1 Wash the Core!	98
	2.3.2 Use all the Core and Remove it from the Core Boxes	99
	2.3.3 Laying Out Intervals of Core for Fracture Logging	99
	2.3.4 Core?Logging Toolkit	100
	2.3.5 Recording Data	101
	2.3.6 Making and Using a Master Orientation Line	102
	2.3.7 Differentiating Natural from Induced Fractures	103
	2.4 Taking, Measuring and Analyzing Fracture Data	104
	2.4.1 Fracture Type	104
	2.4.2 Fracture Depths: Intensity and Density	106
	2.4.3 Fracture Dip Angles	108
	2.4.3.1 Measuring Dip Angles	108
	2.4.3.2 Using Dip Angles	109
	2.4.4 Fracture Distributions	110
	2.4.5 Fracture Heights and Terminations	111
	2.4.6 Fracture Widths, Apertures, and Mineralization	114
	2.4.7 Fracture Spacings	118
	2.4.7.1 Spacings from Horizontal Core	119
	2.4.7.2 Spacings from Vertical Core	123
	2.4.7.3 Converting Vertical Observations to Horizontal Fracture Spacings	123
	2.4.7.4 Spacings of Inclined and Shear Fractures	125
	2.4.7.5 Uses of Spacings	125
	2.4.8 Measuring and Using Fracture Strikes	125
	2.4.8.1 Measuring Fracture Strikes in Vertical Core	126
	2.4.8.2 Measuring Fracture Strikes in Deviated or Horizontal Cores	129
	2.5 New Core vs. Archived Core	130
	2.6 Oriented Core	132
	2.6.1 Other Ways of Orienting a Core	136
	2.7 Using CT Scans	138
	2.8 Fracture Data from Image Logs	139
	2.9 Comparing Fracture Data from Outcrops, Core, and Logs	142
	2.9.1 Introduction	142
	2.9.2 Large?Scale Outcrop Studies	143
	2.9.3 Local Outcrop Studies	143
	2.9.3.1 Raton Basin	143
	2.9.3.2 Rifle Gap	145
	2.9.3.3 San Ysidro	147
	2.10 Fracture Data from 3D Seismic SurveysDr. Bruce Hart provided significant and much?appreciated input into this section.	148
	2.11 Fracture Data Acquired by LiDAR	150
	2.12 Fracture Data from Engineering Tests	152
	2.13 Case Studies in Estimating Fracture Effectiveness from Core	153
	2.13.1 Introduction	153
	2.13.2 Case Study 1: Archived Vertical, Unoriented Core	153
	2.13.3 Case Study 2: New, Un?Slabbed Horizontal Core	154
	2.13.3.1 Introduction	154
	2.13.3.2 Fracture Effectiveness	157
	2.13.3.3 System Effectiveness and Permeability Anisotropy	157
	2.13.4 Case Study 3: New, Slabbed, Vertical Core	159
	2.13.4.1 Introduction	159
	2.13.4.2 Calculating Effectiveness	159
	2.13.4.3 Description of the High?Angle Extension Fractures	161
	Appendix 2.A Workflow and List of Tests, Data	164
	Appendix 2.B Core-Handling, Marking, Sampling, and Analysis Protocol for Core Studies Focused on Natural Fractures	164
	Appendix 2.C Slabbing Recommendations for Horizontal Core	166
	Part 3 Effects of Natural Fractures on Reservoirs	169
	3.1 Introduction	169
	3.2 Classification	169
	3.3 The Permeability Behavior of Individual Fractures	170
	3.3.1 Introduction	170
	3.3.2 Three Categories of Fracture Effects	170
	3.3.3 Stylolites	174
	3.3.4 Microfractures	174
	3.4 The Effects of Fracture Systems	176
	3.4.1 Introduction	176
	3.4.2 Fracture?Controlled Permeability Anisotropy	177
	3.4.2.1 Case Study: The Midale Field	177
	3.4.2.2 Case Study: The Rulison Field	178
	3.4.2.3 Case Study: The Spraberry Formation	178
	3.4.3 Fracture?Controlled Sweet Spots	182
	3.5 The Sensitivity of Fracture Permeability to Changing Stress	184
	3.5.1 Stress?Sensitive Extension Fractures	184
	3.5.1.1 Case Study: The Bulo Bulo Field	187
	3.5.2 Stress?Sensitive Shear Fractures	189
	3.5.3 Damage Due to Production?Related Scale	191
	3.6 Fracture Volumetrics	192
	3.6.1 Introduction	192
	3.6.2 Fracture Volume/Fracture Porosity	193
	3.6.3 Fracture Permeability	194
	3.6.4 Transfer Function	196
	3.6.5 Fracture Surface Areas	196
	3.7 Effects of Fractures on Drilling and Coring	197
	3.8 Completions: The Interaction Between Natural and Hydraulic Fractures	198
	3.8.1 Early Conceptual Models	198
	3.8.2 Direct Evidence of the Characteristics of Hydraulic Fractures	199
	3.8.3 The Developing Hydraulic?Fracture Model	202
	3.8.4 Nuclear Stimulations	204
	References	207
	Index	225
	EULA	232