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viii Contents

6. Gas Compressors 119
6.1 Introduction 119
6.2 Gas Flow Mechanics 119
6.3 Gas Injection Rate Requirements 128
6.4 Gas Injection Pressure Requirements 138
6.5 Horsepower Requirements 142
Summary 144

7. Gas Drilling Operations 147
7.1 Introduction 147
7.2 Gas Drilling Procedures 147
7.3 Problems and Solutions 150
Summary 163
Part Three Underbalanced Drilling Systems 165

8. Equipment in Underbalanced Drilling Systems 167
8.1 Introduction 167
8.2 Surface Equipment 167
8.3 Downhole Equipment 170
Summary 171

9. Gas and Liquid Injection Rates 173
9.1 Introduction 173
9.2 Multiphase Flows in UBD Systems 173
9.3 The Gas-Liquid Flow Rate Window 194
Summary 209

10. Underbalanced Drilling Operations 213
10.1 Introduction 213
10.2 Aerated Liquid Drilling 213
10.3 Foam Drilling 223
Summary 230

Appendix A Unit Conversion Factors 231
Appendix B Minimum Gas Flow Rates Required for Lifting Solids
and Water in Air Drilling 233
Appendix C API Drill Collar Weight (lb/ft) 241
Appendix D API Drill Pipe Dimensional Data 243
Appendix E API Casing Dimensional Data 245
Index 255