List of Figures .............................................. xiii
Preface ....................................................... xxi
1 Introduction ................................................. 1
Dendy Sloan
1.1 Why Are Hydrates Important? ............................. 1
1.2 What Are Hydrates? ...................................... 2
1.2.1 Hydrate Crystal Structures ....................... 2
1.3 Four Rules of Thumb Arising from Crystal Structure ...... 4
1.4 Chapter Summary Application: Methane Hydrate Formation
on an Emulsified Water Droplet .......................... 9
References .................................................. 11
2 Where and How Are Hydrate Plugs Formed? ..................... 13
Dendy Sloan, Jefferson Creek, and Amadeu K. Sum
2.1 Where Do Hydrates Form in Offshore Systems? ............ 13
2.2 How Do Hydrate Plugs Form? Four Conceptual Pictures .... 16
2.2.1 Hydrate Blockages in Oil-Dominated Systems ...... 17
2.2.1.1 Rules of Thumb for Hydrate Formation
in Oil-Dominated Systems ............... 18
2.2.1.2 A Model for Hydrate Formation in
Oil-Dominated Flowlines ................ 19
2.2.2 Hydrate Formation in Gas-Condensate Systems ..... 22
2.2.2.1 Case Study 1: Tommeliten-Gamma Field ... 22
2.2.2.2 Case Study 2: Werner-Bolley Field
Hydrate Formation ...................... 24
2.2.2.3 Hypothesized Mechanism for Gas-
Dominated Systems ...................... 26
2.2.3 Hydrate Blockages in Condensate Flowlines ....... 27
2.2.4 High-Water-Cut (Volume) Systems ................. 31
2.3 Risk Management in Hydrate Plug Prevention ............. 32
2.3.1 Cold Stabilized Flow ............................. 33
2.4 Relationship of Chapter to Subsequent Content .......... 35
References .................................................. 35
3 Safety in Hydrate Plug Removal .............................. 37
Carolyn Koh and Jefferson Creek
3.1 Two Safety Case Studies ................................ 37
3.1.1 Case Study 1: One-Sided Depressurization ........ 37
3.1.1.1 The Cause and Effect of Hydrate
Projectiles ............................ 38
3.1.1.2 Predicting Plug Projectile Effects ..... 41
3.1.1.2.1 Example Calculation .......... 44
3.1.1.3 The Effect of Multiple Plugs ........... 45
3.1.2 Case Study 2: Heating a Plug .................... 45
3.2 Common Circumstances of Plug Formation and Plug
Removal Safety ......................................... 46
3.2.1 Common Circumstances of Plug Formation .......... 46
3.2.2 Plug Removal Safety Recommendations ............. 46
3.3 Relationship of Chapter to Subsequent Content .......... 47
References .................................................. 47
4 How Hydrate Plugs Are Remediated ............................ 49
Norm McMullen
4.1 Introduction ........................................... 50
4.2 Safety Concerns ........................................ 51
4.3 Blockage Identification ................................ 52
4.3.1 Determining Cause of Blockage .................... 53
4.4 Locating Blockage ...................................... 54
4.5 Determining Blockage Size .............................. 55
4.6 Blockage Removal Options ............................... 56
4.6.1 Pressure ........................................ 57
4.6.2 Chemical ........................................ 58
4.6.3 Mechanical ...................................... 58
4.6.4 Thermal ......................................... 59
4.6.4.1 Heated Bundle .......................... 60
4.6.4.2 Electrical Heating ..................... 61
4.6.4.3 Heating Tent ........................... 61
4.6.4.4 Mud or Fluid Circulation ............... 61
4.6.4.5 External Heat Tracing .................. 62
4.6.4.6 Guiding Principles for Thermal
Remediation ............................ 62
4.7 Removal Strategies ..................................... 63
4.7.1 Pipelines/Flowlines Strategy .................... 63
4.7.1.1 Recommended Order of Consideration ..... 64
4.7.1.2 Detailed Discussion of Pipelines/
Flowlines Strategy ..................... 64
4.7.1.2.1 Pressure Method .............. 64
4.7.1.2.2 Chemical Management ......... 65
4.7.1.2.3 Mechanical Method ........... 65
4.7.1.2.4 Thermal Method ............... 66
4.7.2 Wells Strategy .................................. 66
4.7.2.1 Recommended Order of Consideration ..... 67
4.7.2.2 Detailed Discussion of Well Strategy ... 67
4.7.2.2.1 Pressure Method ............. 67
4.7.2.2.2 Chemical Method ............. 68
4.7.2.2.3 Mechanical Method ........... 68
4.7.2.2.4 Thermal Method .............. 68
4.7.3 Risers Strategy ................................. 69
4.7.3.1 Recommended Order of Consideration ..... 69
4.7.3.2 Detailed Discussion of Riser
Strategy ............................... 70
4.7.3.2.1 Pressure Method ............. 70
4.7.3.2.2 Chemical Method ............. 70
4.7.3.2.3 Mechanical Method ........... 71
4.7.3.2.4 Thermal Method .............. 71
4.7.4 Equipment Strategy .............................. 72
4.7.4.1 Recommended Order of Consideration ..... 72
4.7.4.2 Detailed Discussion of Remediation
Strategy ............................... 72
4.7.4.2.1 Pressure Method ............. 72
4.7.4.2.2 Chemical Method ............. 73
4.7.4.2.3 Mechanical Method ........... 73
4.7.4.2.4 Thermal Method .............. 74
4.8 Case Studies ........................................... 75
4.8.1 Export Pipeline (BP Pompano) .................... 75
4.8.1.1 Strategy Employed to Dissociate the
Plug ................................... 76
4.8.2 Gas Condensate Pipeline (Chevron) ............... 77
4.8.3 Well (Gas Condensate) ........................... 78
4.8.4 Equipment (BP Gulf of Mexico) ................... 78
References .................................................. 81
Appendix .................................................... 82
5 Artificial and Natural Inhibition of Hydrates ............... 87
Thierry Palermo and Dendy Sloan
5.1 How Thermodynamic Hydrate Inhibitors Function and How
They Are Used .......................................... 88
5.2 The Low Dosage Hydrate Inhibitors (LDHIs) .............. 92
5.2.1 Kinetic Hydrate Inhibitors ...................... 92
5.2.2 Anti-Agglomerants ............................... 95
5.3 Naturally Inhibited Oils ............................... 97
5.3.1 Viscosity of Suspension ......................... 98
5.3.2 Viscosity of Aggregated Suspension .............. 98
5.3.3 Methodology .................................... 100
5.3.4 Prediction ..................................... 101
5.4 Conclusion ............................................ 103
References ................................................. 103
6 Kinetic Hydrate Inhibitor Performance ...................... 105
Mike Eaton, Jason Lachance, and Larry Talley
6.1 Introduction .......................................... 105
6.2 Study 1: Miniloop Flowing KHI Hold Time ............... 106
6.3 Study 2: Autoclave Testing Methodology ................ 111
6.3.1 Introduction ................................... 112
6.3.2 Miniloop Equivalence Requirements .............. 114
6.3.3 Device Design .................................. 116
6.3.4 Test Procedures and Data Interpretation ........ 120
6.3.4.1 Teq Tests .............................. 120
6.4 Hold-Time Tests ....................................... 128
6.4.1 Autoclave Study Summary ........................ 132
6.5 Study 3: Correlation of Miniloop, Large Loop, and
Rocking Cell Results .................................. 132
6.6 Study 4 - Correlation of Large Loop and Field
Results ............................................... 133
6.7 Conclusion ............................................ 134
References ................................................. 135
Appendix ................................................... 136
7 Industrial Operating Procedures for Hydrate Control ........ 145
Adam Ballard, George Shoup, and Dendy Sloan
7.1 Introduction .......................................... 145
7.2 Deepwater System Design ............................... 146
7.3 Applications of Chapters 1 through 6 .................. 147
7.3.1 Question 1: When and Where Are Hydrates
Likely to Form in the Production System? ....... 148
7.3.2 Question 2: What Can I Control in Order to
Prevent Hydrates from Forming? ................. 148
7.3.3 Question 3: What Are the Monitoring Points in
the System That Will Give Indication of
Hydrates? ...................................... 149
7.3.3.1 Risk of Hydrate Plugging .............. 150
7.3.3.2 Signs of Hydrate Plugging ............. 150
7.3.4 Question 4: If a Hydrate Plug Forms in the
Production System, How Can It Be Remediated? ... 151
7.3.4.1 Inject Chemical ....................... 152
7.3.4.2 Stop Flow ............................. 152
7.3.4.3 Reduce Flow ........................... 152
7.3.4.4 Increase Flow ......................... 152
7.4 Generation of Operating Procedures for Hydrate
Control ............................................... 153
7.4.1 Detailed Design-Customer: Engineering .......... 153
7.4.2 Operating Guidelines-Customer: Engineering
and Operations ................................ 153
7.4.3 Operating Procedures-Customer: Operations ...... 154
7.5 Operating Procedure Details ........................... 155
7.5.1 Who Is the Customer? ........................... 156
7.5.2 Writing an Operating Procedure ................. 157
7.6 Sample Operating Procedure: Cold Well Startup into
Cold System .......................................... 160
7.6.1 Pre-Startup Checklist .......................... 161
7.6.2 Restart Guidelines ............................. 161
7.7 Relationship of Chapter to Others in This Book ........ 162
References ................................................. 162
8 Conclusion ................................................. 163
8.1 Chapter 1. Basic Structures and Formation
Properties ............................................ 164
8.2 Chapter 2. How Hydrate Plugs Form and Are Prevented ... 165
8.3 Chapter 3. Hydrate Safety during Remediation .......... 166
8.4 Chapter 4. Industrial Methods for Hydrate Plug
Dissociation .......................................... 167
8.5 Chapter 5. Inhibitor Mechanisms and Naturally
Inhibited Oils ........................................ 167
8.6 Chapter 6. Certifying Hydrate Kinetic Inhibitors for
Field Performance ..................................... 169
8.7 Chapter 7. Offshore Production Operating Procedures
for Hydrate Control .................................. 169
Appendix Six Industrial Hydrate Blockage Examples and
Lessons Learned ...................................... 171
Index ......................................................... 193
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