Fundamentals of Gas Shale Reservoirs

Reza Rezaee is a Professor in the Department of Petroleum Engineering at Curtin University, Australia. He is the winner of Australian Gas innovation research 2012 award for introducing a new method to enhance natural gas production from tight gas reservoirs. He has published more than 120 peer-reviewed journal and conference papers and is the author of 3 books. His current research has been focused on integrated reservoir characterization, formation evaluation and petrophysics. He is a former “Research Fellow”, School of Geology and Geophysics, Oklahoma University.

Contributors xv

Preface xvii

1 Gas Shale: Global Significance Distribution and Challenges 1

1.1 Introduction 1

1.2 Shale Gas Overview 1

1.2.1 Shale Gas Geology 2

1.2.2 Characteristics of a Producing Shale Gas Play 3

1.3 The Significance of Shale Gas 4

1.4 Global Shale Gas Resources 5

1.4.1 Sources of Information 5

1.4.2 Resource Estimation Methodologies 5

1.5 Global Resource Data 7

1.5.1 China 7

1.5.2 The United States 7

1.5.3 Mexico 7

1.5.4 Southern South America 7

1.5.5 South Africa 8

1.5.6 Australia 8

1.5.7 Canada 8

1.5.8 North Africa 8

1.5.9 Poland 9

1.5.10 France 9

1.5.11 Russia 9

1.5.12 Scandinavia 9

1.5.13 Middle East 9

1.5.14 India 9

1.5.15 Pakistan 10

1.5.16 Northwest Africa 10

1.5.17 Eastern Europe (Outside of Poland) 10

1.5.18 Germany and Surrounding Nations 10

1.5.19 The United Kingdom 10

1.5.20 Northern South America 11

1.5.21 Turkey 11

1.6 Data Assessment 11

1.6.1 Distribution 11

1.6.2 Basin Type 11

1.6.3 Depositional Environment 12

1.6.4 TOC Content 12

1.6.5 Clay Content 13

1.7 Industry Challenges 13

1.7.1 Environmental Challenges 13

1.7.2 Commercial/Economic 14

1.8 Discussion 14

1.9 Conclusions 15

Appendix A.1 Global Shale Gas Resource Data 16

2 Organic Matter]Rich Shale Depositional Environments 21

2.1 Introduction 21

2.2 Processes Behind the Deposition of Organic Matter]Rich Shale 23

2.2.1 Processes Behind the Transport and Deposition of Mud 23

2.2.2 Production Destruction and Dilution: The Many Roads to Black Shale 23

2.3 Stratigraphic Distribution of Organic Matter]Rich Shales 25

2.4 Geographic Distribution of Organic Matter]Rich Shales 27

2.4.1 Background 27

2.4.2 Controls on the Geographic Distribution of Black Shales 30

2.5 Organic Matter]Rich Shale Depositional Environments 34

2.5.1 Continental Depositional Environments 34

2.5.2 Paralic Depositional Environments 36

2.5.3 Shallow Marine Depositional Environments 37

2.5.4 Deep Marine Depositional Environments 38

2.6 Conclusion 39

3 Geochemical Assessment of Unconventional Shale Gas Resource Systems 47

3.1 Introduction 47

3.2 Objective and Background 49

3.3 Kerogen Quantity and Quality 49

3.4 Sample Type and Quality 51

3.5 Kerogen Type and Compositional Yields 52

3.6 Thermal Maturity 54

3.7 Organoporosity Development 55

3.8 Gas Contents 57

3.9 Expulsion–Retention of Petroleum 57

3.10 Secondary (Petroleum) Cracking 58

3.11 Upper Maturity Limit for Shale Gas 58

3.12 Gas Composition and Carbon Isotopes 59

3.13 Additional Geochemical Analyses for Shale Gas Resource System Evaluation 61

3.14 Oil and Condensate with Shale Gas 63

3.15 Major Shale Gas Resource Systems 64

3.16 Conclusions 65

4 Sequence Stratigraphy of Unconventional Resource Shales 71

4.1 Introduction 71

4.2 General Sequence Stratigraphic Model for Unconventional Resource Shales 71

4.3 Ages of Sea]Level Cycles 72

4.4 Water Depth of Mud Transport and Deposition 73

4.5 Criteria to Identify Sequences and Systems Tracts 74

4.6 Paleozoic Resource Shale Examples 74

4.6.1 Barnett Shale (Devonian) 74

4.6.2 Woodford Shale (Late Devonian–Early Mississippian) 74

4.6.3 Marcellus Shale (Devonian) 78

4.6.4 New Albany Shale (Upper Devonian–Lower Mississippian) 78

4.7 Mesozoic Resource Shale Examples 80

4.7.1 Montney Formation (Early Triassic) 80

4.7.2 Haynesville/Bossier Shales (Late Jurassic) 80

4.7.3 Eagle Ford Formation (Cretaceous) 80

4.7.4 LaLuna Formation (Upper Cretaceous) 82

4.8 Cenozoic Resource Shale Example 83

4.9 Conclusions 84

4.10 Applications 84

5 Pore Geometry in Gas Shale Reservoirs 89

5.1 Introduction 89

5.1.1 Gas Shales and Their Challenges 89

5.1.2 Pore Size Classification 90

5.2 Samples Characteristics 90

5.2.1 Sample Collection 90

5.2.2 Mineral Composition 90

5.3 Experimental Methodology 91

5.3.1 Capillary Pressure Profile 91

5.3.2 Nitrogen Adsorption (N2) 92

5.3.3 Low]Field NMR 92

5.3.4 Image Acquisition and Analysis 93

5.4 Advantages and Disadvantages of Experimental PSD Methods 95

5.5 Permeability Measurement 95

5.6 Results 96

5.6.1 Pore Size Distribution from MICP Experiments 96

5.6.2 Pore Size Distribution from Nitrogen Adsorption Experiments 98

5.6.3 NMR T2 Relaxation Time 98

5.6.4 Scanning Electron Microscopy 100

5.6.5 Focused Ion Beam/Scanning Electron Microscopy 100

5.6.6 Capillary Pressure and Permeability 102

5.7 Discussion 103

5.7.1 Porosity and PSD Comparisons 103

5.7.2 Interchanging MICP with NMR Data 103

5.7.3 Pore]Body to Pore]Throat Size Ratio: Pore Geometry Complexity 107

5.7.4 Pore Throat Size and Permeability 107

5.7.5 Mineralogy 108

5.8 Conclusions 112

Appendix 5.A XRD Results 114

6 Petrophysical Evaluation of Gas Shale Reservoirs 117

6.1 Introduction 117

6.2 Key Properties for Gas Shale Evaluation 117

6.2.1 Pore System Characteristics 117

6.2.2 Organic Matter Characteristics 118

6.2.3 Permeability 118

6.2.4 Gas Storage Capacity 119

6.2.5 Shale Composition 120

6.2.6 Geomechanical Properties 120

6.3 Petrophysical Measurements of Gas Shale Reservoirs 121

6.3.1 Pore Structure Evaluation Techniques 121

6.3.2 Fluid Saturation Measurement 122

6.3.3 Permeability Measurement 123

6.3.4 Adsorbed Gas Measurement 124

6.4 Well Log Analysis of Gas Shale Reservoirs 125

6.4.1 Well Log Signatures of Gas Shale Formations 125

6.4.2 Well Log Interpretation of Gas Shale Formations 128

7 Pore Pressure Prediction for Shale Formations Using well Log Data 139

7.1 Introduction 139

7.1.1 Normal Pressure 139

7.1.2 Overpressure 139

7.2 Overpressure-Generating Mechanisms 140

7.2.1 Loading Mechanisms 141

7.2.2 Unloading Mechanisms (Fluid Expansion) 142

7.2.3 World Examples of Overpressures 143

7.2.4 Overpressure Indicators from Drilling Data 144

7.2.5 Identification of Shale Intervals 144

7.3 Overpressure Estimation Methods 146

7.3.1 Overview of the Compaction Theory 146

7.3.2 Eaton’s Method 147

7.3.3 Effective Stress Method 149

7.3.4 Bowers’s Method 150

7.4 The Role of Tectonic Activities on Pore Pressure In Shales 151

7.4.1 Geology of the Study Area 151

7.4.2 Stress Field in the Perth Basin 152

7.4.3 Pore Pressure in Tectonically Active Regions (Uplifted Areas) 154

7.4.4 Pore Pressure in Tectonically Stable Regions 154

7.4.5 Origins of Overpressure in Kockatea Shale 156

7.5 Discussion 160

7.5.1 Significance of Pore Pressure Study 163

7.5.2 Overpressure Detection and Estimation 163

7.5.3 Pore Pressure and Compressional Tectonics 163

7.5.4 Overpressure-Generating Mechanisms 164

7.5.5 Overpressure Results Verifications 164

7.6 Conclusions 165

8 Geomechanics of Gas Shales 169

8.1 Introduction 169

8.2 Mechanical Properties of Gas Shale Reservoirs 170

8.2.1 Gas Shale Reservoir Properties under Triaxial Loading 170

8.2.2 True]Triaxial Tests 171

8.2.3 Gas Shale Reservoir Properties under Ultrasonic Tests 172

8.2.4 Nanoindentation Tests on Gas Shale Plays 173

8.2.5 Scratch Tests 174

8.3 Anisotropy 175

8.3.1 Anisotropy in Gas Shale Reservoirs 175

8.4 Wellbore Instability in Gas Shale Reservoirs 176

8.4.1 Structurally Controlled Instability 177

8.4.2 Instability Due to Directional Dependency of Geomechanical Parameters 178

8.4.3 Time]Dependent Instability 184

9 Rock Physics Analysis of Shale Reservoirs 191

9.1 Introduction 191

9.2 Laboratory Measurements on Shales: Available Datasets 192

9.3 Organic Matter Effects on Elastic Properties 192

9.4 Partial Saturation Effects 195

9.5 Maturity Effects 197

9.6 Seismic Response of Orss 201

9.7 Conclusions 203

10 Passive Seismic Methods for Unconventional Resource Development 207

10.1 Introduction 207

10.2 Geomechanics and Natural Fracture Basics for Application to Hydraulic Fracturing 209

10.2.1 Basics of Earth Stress and Strain 209

10.2.2 Natural Fracture Basics and Interaction with Hydraulic Fractures 211

10.3 Seismic Phenomena 213

10.3.1 MEQs and Their Magnitudes 213

10.3.2 Earthquake Focal Mechanisms 213

10.3.3 Other Types of Seismic Activity Produced by Hydraulic Fracturing 216

10.4 Microseismic Downhole Monitoring 216

10.4.1 Downhole Monitoring Methodology 216

10.4.2 Advantages and Disadvantages of Downhole Monitoring 220

10.5 Monitoring Passive Seismic Emissions with Surface and Shallow Buried Arrays 222

10.5.1 Recording 222

10.5.2 Seismic Emission Tomography 223

10.5.3 MEQ Methods 229

10.5.4 Imaging Cumulative Seismic Activity 230

10.5.5 Direct Imaging of Fracture Networks 232

10.5.6 Comparison of Downhole Hypocenters and Fracture Images 232

10.5.7 Summary 233

10.6 Integrating Interpreting and Using Passive Seismic Data 235

10.6.1 General Considerations 235

10.6.2 Interpreting Reservoir Stress from Focal Mechanisms 236

10.6.3 Fracture Width Height SRV and Tributary Drainage Volume 240

10.6.4 Using Passive Seismic Results for Frac Well]Test and Reservoir Simulation 240

10.7 Conclusions 241

11 Gas Transport Processes in Shale 245

11.1 Introduction 245

11.2 Detection of Nanopores in Shale Samples 247

11.3 Gas Flow in Micropores and Nanopores 248

11.4 Gas Flow in a Network of Pores in Shale 251

11.5 Gas Sorption in Shale 252

11.6 Diffusion in Bulk Kerogen 253

11.7 Measurement of Gas Molecular Diffusion into Kerogen 255

11.8 Pulse]Decay Permeability Measurement Test 256

11.8.1 Pulse]Decay Pressure Analysis 257

11.8.2 Estimation of Permeability Parameters with the Pulse]Decay Experiment 259

11.9 Crushed Sample Test 260

11.9.1 Porosity Measurement 260

11.9.2 Crushed Sample Pressure Analysis for Permeability Measurement 261

11.9.3 Crushed Sample Permeability Estimation with Early]Time Pressure Data 262

11.9.4 Crushed Sample Permeability Estimation with Late]Time Pressure Data 262

11.10 Canister Desorption Test 262

11.10.1 Permeability Estimation with Early Time Cumulative Desorbed Gas Data 263

11.10.2 Permeability Estimation with Late]Time Cumulative Desorbed Gas Data 264

12 A Review of the Critical Issues Surrounding the Simulation of Transport and Storage in Shale Reservoirs 267

12.1 Introduction 267

12.2 Microgeometry of Organic]Rich Shale Reservoirs 268

12.3 Gas Storage Mechanisms 269

12.4 Fluid Transport 270

12.5 Capillary Pressure Relaxation to Equilibrium State and Deposition of Stimulation Water 273

12.6 Characterization of Fluid Behavior and Equations of State Valid for Nanoporous Media 274

12.6.1 Viscosity Corrections 276

12.6.2 Corrections for Interfacial Tension 277

12.7 Upscaling Heterogeneous Shale]Gas Reservoirs into Large Homogenized Simulation Grid Blocks 277

12.7.1 Upscaling Fine Continuum Model of Shale to Lumped]Parameter Leaky Tank Model of Shale 278

12.7.2 Upscaling Finely Detailed Continuum Model of Shale to Coarse Continuum Model of Shale 279

12.8 Final Remarks 280

13 Performance Analysis of Unconventional Shale Reservoirs 283

13.1 Introduction 283

13.2 Shale Reservoir Production 283

13.3 Flow Rate Decline Analysis 284

13.3.1 Decline Curve Analysis in Unconventional Reservoirs 285

13.3.2 Flow Rate Transient Analysis (RTA) and its Relation to Rate Decline Analysis 286

13.3.3 Field Applications 287

13.4 Flow Rate and Pressure Transient Analysis in Unconventional Reservoirs 288

13.4.1 Bilinear Flow Regime in Multistage Hydraulic Fracturing 288

13.4.2 Linear Flow Analysis for Reservoir Permeability 289

13.4.3 Field Applications 290

13.4.4 Type-Curve Matching 290

13.5 Reservoir Modeling and Simulation 292

13.5.1 History Matching and Forecasting 292

13.5.2 Dual-Porosity Single-Phase Modeling 293

13.5.3 Dual-Porosity Multicomponent Gas Modeling 294

13.6 Specialty Short-Term Tests 295

13.6.1 Mini-DST 295

13.6.2 Mini-Frac Test 296

13.7 Enhanced Oil Recovery 297

13.8 Conclusion 298

14 Resource Estimation for Shale Gas Reservoirs 301

14.1 Introduction 301

14.1.1 Unique Properties of Shale 301

14.1.2 Petroleum Resources Management System (PRMS) 301

14.1.3 Energy Information Administration’s Classification System 301

14.1.4 Reserves Estimate Methodology for Unconventional Gas Reservoirs 302

14.1.5 Monte Carlo Probabilistic Approach 302

14.1.6 Analytical Models 303

14.1.7 Economic Analysis 303

14.1.8 Region]Level World Shale Gas Resource Assessments 304

14.1.9 Shale Gas OGIP Assessment in North America 305

14.1.10 Recent Shale Gas Production and Activity Trends 306

14.1.11 Drilling Stimulation and Completion Methods in Shale Gas Reservoirs 308

14.2 Methodology 309

14.3 Resource Evaluation of Shale Gas Plays 310

14.3.1 Reservoir Model 310

14.3.2 Well Spacing Determination 310

14.3.3 Reservoir Parameters Sensitivity Analysis 311

14.3.4 Reservoir Parameters 312

14.3.5 Model Verification 312

14.3.6 Resource Assessment 313

14.3.7 Reserve Evaluation 318

14.4 Discussion 320

15 Molecular Simulation of Gas Adsorption in Minerals and Coal: Implications for Gas Occurrence in Shale Gas Reservoirs 325

15.1 Introduction 325

15.1.1 Molecular Dynamics Simulation 325

15.1.2 Major Challenges in Shale Gas Research 326

15.1.3 MS of Gas Adsorption 326

15.1.4 Methodology and Workflow of Molecular Simulation 327

15.1.5 Simulation Algorithms and Software 327

15.2 MS of Gas Adsorption on Minerals 327

15.2.1 MD Simulation of Gas Adsorption on Quartz 328

15.2.2 Molecular Dynamic Simulation of Gas Adsorption on Wyoming]Type Montmorillonite 330

15.2.3 MD Simulation of Gas Adsorption on Zeolite 332

15.2.4 MD Simulation of Gas Adsorption on Coal 334

15.3 Conclusions 337

16 Wettability of Gas Shale Reservoirs 341

16.1 Introduction 341

16.2 Wettability 341

16.3 Imbibition in Gas Shales 342

16.4 Factors Influencing Water Imbibition in Shales 343

16.4.1 Sample Expansion 343

16.4.2 Depositional Lamination 346

16.4.3 Chemical Osmosis 346

16.4.4 Water Film and Salt Crystals 348

16.4.5 Water Adsorption (Clay Swelling) 348

16.4.6 Connectivity of Hydrophobic and Hydrophilic Pore Networks 349

16.4.7 Effect of Polymer and Surfactant 351

16.5 Quantitative Interpretation of Imbibition Data 352

16.5.1 Scaling Imbibition Data 352

16.5.2 Modeling Imbibition Data 352

16.6 Estimation of Brine Imbibition at the Field Scale 354

16.7 Initial Water Saturation in Gas Shales 356

16.8 Conclusions 356

17 Gas Shale Challenges Over The Asset Life Cycle 361

17.1 Introduction 361

17.2 The Asset Life Cycle 361

17.2.1 Exploration Phase Objectives—Recommended Practices 361

17.2.2 Appraisal Phase Objectives—Recommended Practices 362

17.2.3 Development Phase Objectives—Recommended Practices 362

17.2.4 Production Phase Objectives—Recommended Practices 362

17.2.5 Rejuvenation Phase Objectives—Recommended Practices 362

17.3 Exploration Phase Discussion 362

17.3.1 Screening Study—Current Practice 362

17.3.2 Screening Study Recommended Practices 363

17.3.3 Reservoir Characterization—Current Practice 363

17.3.4 Reservoir Characterization—Recommended Practices 363

17.3.5 Determining Initial Economic Value and Reservoir Potential 365

17.4 Appraisal Phase Discussion 365

17.4.1 Drill Appraisal Wells—Current Practice 365

17.4.2 Drill Appraisal Wells—Recommended Practices 365

17.4.3 Build Reservoir Models for Simulation—Current Practice 365

17.4.4 Build Reservoir Models for Simulation—Recommended Practices 365

17.4.5 Generate a Field Development Plan—Current Practice 366

17.4.6 Generate a Field Development Plan—Recommended Practices 366

17.4.7 Validate Economics of the Play or Pilot Project 366

17.5 Development Phase Discussion 367

17.5.1 Implement the Field Development Plan 367

17.5.2 Surface Facilities 367

17.5.3 Design Wells and Optimize Drilling Costs—Current Practice 367

17.5.4 Design Wells and Optimize Drilling Costs—Recommended Practice 368

17.5.5 Refine and Optimize Hydraulic Fracturing and Wellbore Completion Design—Current Practices (Characterize the Lateral) 369

17.5.6 Current Hydraulic Fracturing Practices 369

17.5.7 Hydraulic Fracturing—Recommended Practices 370

17.5.8 Characterize the Lateral 372

17.5.9 Current Wellbore Completion Practice 373

17.5.10 Wellbore Completion—Recommended Practices 373

17.5.11 Drilling Considerations for Completion Methods 375

17.5.12 Fracturing Considerations for Completion Method 375

17.6 Production Phase Discussion 375

17.6.1 Monitor and Optimize Producing Rates—Current Practice 375

17.6.2 Monitor and Optimize Producing Rates—Recommended Practices 375

17.6.3 Manage the Water Cycle—Recommended Practices 376

17.6.4 Preventing Corrosion Scaling and Bacterial Contamination in Wells and Facilities 376

17.6.5 Protecting the Environment 376

17.7 Rejuvenation Phase Discussion 376

17.8 Conclusions—Recommended Practices 377

18 Gas Shale Environmental Issues and Challenges 381

18.1 Overview 381

18.2 Water Use 381

18.3 The Disposal and Reuse of Fracking Wastewater 382

18.4 Groundwater Contamination 384

18.5 Methane Emissions 386

18.6 Other Air Emissions 387

18.7 Social Impacts on Shale Gas Communities 388

18.8 Induced Seismicity: Wastewater Injection and Earthquakes 388

18.9 Regulatory Developments 389

18.10 Disclosure of Fracking Chemicals 389

18.11 At the Federal Government Level 390

18.12 Conclusion 391

Index 397