Preface ....................................................... xix
Authors ....................................................... xxv
Chapter 1 Overview and Historical Perspective .................. 1
1.1 Hydrates as a Laboratory Curiosity ......................... 1
1.1.1 Hydrates of Hydrocarbons Distinguished from
Inorganic Hydrates and Ice .......................... 5
1.1.2 Methods to Determine the Hydrate Composition ........ 5
1.1.3 Phase Diagrams Provide Hydrate Classification ....... 6
1.2 Hydrates in the Natural Gas Industry ....................... 9
1.2.1 Initial Experiments on Natural Gas Hydrates ......... 9
1.2.2 Initial Correlation of Hydrate Phase Equilibria .... 11
1.2.3 Hydrate Crystal Structures and Hydrate Type
Definitions ........................................ 11
1.2.4 Basis for Current Thermodynamic Models ............. 14
1.2.5 Time-Dependent Studies of Hydrates ................. 16
1.2.6 Work to Enable Gas Production, Transport, and
Processing ......................................... 19
1.2.7 Hydrates in Mass and Energy Storage and
Separation ......................................... 20
1.3 Hydrates as an Energy Resource ............................ 22
1.3.1 In Situ Hydrates ................................... 23
1.3.2 Investigations Related to Hydrate Exploration and
Recovery ........................................... 26
1.4 Environmental Aspects of Hydrates ......................... 27
1.5 Safety Aspects of Hydrates ................................ 27
1.6 Relationship of This Chapter to Those That Follow ......... 28
References ................................................ 29
Chapter 2 Molecular Structures and Similarities to Ice ........ 45
2.1 Crystal Structures of Ice Ih and Natural Gas Hydrates ..... 46
2.1.1 Ice, Water, Hydrogen Bonds, and Clusters ........... 46
2.1.1.1 Ice and Bjerrum defects ................... 46
2.1.1.2 The water molecule ........................ 49
2.1.1.3 Hydrogen bonds ............................ 49
2.1.1.4 Hydrogen bonds cause unusual water, ice,
and hydrate properties .................... 50
2.1.1.5 Pentamers and hexamers .................... 52
2.1.2 Hydrate Crystalline Cavities and Structures ........ 53
2.1.2.1 The cavities in hydrates .................. 53
2.1.2.2 Hydrate crystal cells-structures I, II,
and H ..................................... 59
2.1.3 Characteristics of Guest Molecules ................. 72
2.1.3.1 Chemical nature of guest molecules ........ 72
2.1.3.2 Geometry of the guest molecules ........... 73
2.1.3.3 Filling the hydrate cages ................. 85
2.1.4 Summary Statements for Hydrate Structure ........... 91
2.2 Comparison of Properties of Hydrates and Ice .............. 92
2.2.1 Spectroscopic Implications ......................... 93
2.2.2 Mechanical Properties .............................. 95
2.2.2.1 Mechanical strength ....................... 95
2.2.2.2 Elastic properties ........................ 96
2.2.3 Thermal Properties ................................. 97
2.2.3.1 Thermal conductivity of hydrates .......... 97
2.2.3.2 Thermal expansion of hydrates and ice .... 101
2.3 The What and the How of Hydrate Structures .......... 102
References ............................................... 102
Chapter 3 Hydrate Formation and Dissociation Processes ....... 113
3.1 Hydrate Nucleation ....................................... 116
3.1.1 Knowledge Base for Hydrate Nucleation ............. 117
3.1.1.1 Key properties of supercooled water ...... 117
3.1.1.2 Solubility of natural gases in water ..... 119
3.1.1.3 Nucleation theory for ice and hydrates ... 121
3.1.1.4 Site of hydrate nucleation ............... 129
3.1.2 Conceptual Picture of Hydrate Nucleation at the
Molecular Level ................................... 130
3.1.2.1 Labile cluster nucleation hypothesis ..... 131
3.1.2.2 Nucleation at the interface hypothesis ... 134
3.1.2.3 Local structuring nucleation hypothesis .. 135
3.1.3 Stochastic Nature of Heterogeneous Nucleation ..... 138
3.1.4 Correlations of the Nucleation Process ............ 142
3.1.4.1 Driving force of nucleation .............. 143
3.1.5 The "Memory Effect" Phenomenon .................... 147
3.1.6 State-of-the-Art for Hydrate Nucleation ........... 149
3.2 Hydrate Growth ........................................... I50
3.2.1 Conceptual Picture of Growth at the Molecular
Level ............................................. 150
3.2.1.1 Crystal growth molecular concepts ........ 150
3.2.1.2 The boundary layer ....................... 152
3.2.2 Hydrate Crystal Growth Processes .................. 155
3.2.2.1 Single crystal growth .................... 155
3.2.2.2 Hydrate film/shell growth at the water-
hydrocarbon interface .................... 156
3.2.2.3 Crystal growth with interfacial
agitation ................................ 166
3.2.2.4 Growth of metastable phases .............. 167
3.2.3 Correlations of the Growth Process ................ 168
3.2.3.1 Growth kinetics-the Englezos-Bishnoi
model .................................... 169
3.2.3.2 Mass transfer-the Skovborg-Rasmussen
model .................................... 171
3.2.3.3 Heat transfer models ..................... 172
3.2.4 State-of-the-Art for Hydrate Growth ............... 176
3.3 Hydrate Dissociation ..................................... 176
3.3.1 Conceptual Picture of Hydrate Dissociation ........ 176
3.3.2 Correlations of Hydrate Dissociation .............. 177
3.3.3 Anomalous Self-Preservation ....................... 179
3.3.4 State-of-the-Art for Hydrate Dissociation ......... 180
3.4 Summary .................................................. 180
References ............................................... 181
Chapter 4 Estimation Techniques for Phase Equilibria of
Natural Gas Hydrates .......................................... 189
Introduction ............................................. 189
4.1 Hydrate Phase Diagrams for Water + Hydrocarbon Systems ... 196
4.1.1 Pressure-Temperature Diagrams of the CH4 + H2O
(or N2 + H20) System .............................. 197
4.1.2 Systems (e.g., H2O + C2H6, C3H8, or 1-C4H10)
with Upper Quadruple Points ....................... 200
4.1.3 Pressure-Temperature Diagrams for Multicomponent
Natural Gas Systems ............................... 201
4.1.4 Pressure-Temperature Diagrams for Systems with
Inhibitors ........................................ 202
4.1.5 Temperature-Composition Diagrams for Methane +
Water ............................................. 202
4.1.6 Solubility of Gases Near Hydrate Formation
Conditions ........................................ 205
4.1.7 Pressure-Temperature Diagrams for Structure H
Systems ........................................... 205
4.2 Three-Phase (Lw-H-V) Equilibrium Calculations ............ 208
4.2.1 The Gas Gravity Method ............................ 209
4.2.1.1 Hydrate limits to gas expansion through
a valve .................................. 212
4.2.2 The Distribution Coefficient (K-vsi-Value)
Method ............................................ 215
4.3 Quadruple Points and Equilibrium of Three Condensed
Phases (Lw-H-Lhc) ........................................ 226
4.3.1 The Location of the Quadruple Points .............. 226
4.3.2 Condensed Three-Phase Equilibrium ................. 227
4.4 Effect of Thermodynamic Inhibitors on Hydrate Formation .. 229
4.4.1 Hydrate Inhibition via Alcohols and Glycols ....... 231
4.4.2 Hydrate Inhibition Using Salts .................... 234
4.5 Two-Phase Equilibrium: Hydrates with One Other Phase ..... 236
4.5.1 Water Content of Vapor in Equilibrium with
Hydrate ........................................... 237
4.5.2 Water Content of Liquid Hydrocarbon in
Equilibrium with Hydrates ......................... 239
4.5.3 Methane Content of Water in Equilibrium with
Hydrates .......................................... 240
4.6 Hydrate Enthalpy and Hydration Number from Phase
Equilibrium .............................................. 240
4.6.1 The Clausius-Clapeyron Equation and Hydrate
Equilibrium ....................................... 241
4.6.1.1 Enthalpy of dissociation and cavity
occupation ............................... 243
4.6.2 Determination of the Hydration Number ............. 246
4.6.2.1 Using the Clapeyron equation to obtain
hydration number ......................... 247
4.6.2.2 Hydration numbers by the Miller and
Strong method ............................ 250
4.7 Summary and Relationship to Chapters Which Follow ........ 252
References ............................................... 252
Chapter 5 A Statistical Thermodynamic Approach to Hydrate
Phase Equilibria .............................................. 257
Introduction and Overview ..................................... 257
5.1 Statistical Thermodynamics of Hydrate Equilibria ......... 258
5.1.1 Grand Canonical Partition Function for Water ...... 259
5.1.2 The Chemical Potential of Water in Hydrates ....... 263
5.1.3 The Langmuir Adsorption Analogy ................... 270
5.1.4 Relating the Langmuir Constant to Cell Potential
Parameters ........................................ 272
5.1.5 Activity Coefficient for Water in the Hydrate ..... 277
5.1.6 Defining the Hydrate Fugacity and Reference
Parameters ........................................ 281
5.1.7 The Gibbs Free Energy Method ...................... 285
5.1.8 Accuracy of CSMGem Compared to Commercial
Hydrate Programs .................................. 291
5.1.9 Ab Initio Methods and the van der Waals and
Platteeuw Method .................................. 293
5.2 Application of the Method to Analyze Systems of Methane
+ Ethane + Propane ....................................... 296
5.2.1 Pure Hydrate Phase Equilibria ..................... 296
5.2.2 Binary Hydrate Phase Equilibria ................... 299
5.2.2.1 Methane + propane hydrates ............... 299
5.2.2.2 Methane + ethane hydrates ................ 299
5.2.2.3 Ethane + propane hydrates ................ 302
5.2.2.4 Ternary hydrate phase equilibria and
industrial application ................... 305
5.3 Computer Simulation: Another Microscopic-Macroscopic
Bridge ................................................... 307
5.3.1 Basic Techniques of Monte Carlo and Molecular
Dynamics Simulation ............................... 308
5.3.1.1 Molecular dynamics ....................... 309
5.3.1.2 Monte Carlo .............................. 310
5.3.2 What Has Been Learned from Molecular Simulation? .. 311
5.4 Chapter Summary and Relationship to Following Chapters ... 313
References ............................................... 314
Chapter 6 Experimental Methods and Measurements of Hydrate
Properties .................................................... 319
6.1 Experimental Apparatuses and Methods for Macroscopic
Measurements ............................................. 320
6.1.1 Measurement Methods for Hydrate Phase Equilibria
and Kinetics ...................................... 320
6.1.1.1 Principles of equilibrium apparatus
development .............................. 327
6.1.1.2 Apparatuses for use above the ice point .. 328
6.1.1.3 Apparatus for use below the ice point .... 334
6.1.1.4 Apparatuses for two-phase equilibria ..... 335
6.1.1.5 Flow loops for hydrate formation
kinetics ................................. 335
6.1.2 Methods for Measurement of Thermal Properties ..... 337
6.1.2.1 Heat capacity and heat of dissociation
methods .................................. 338
6.1.2.2 Methods for thermal conductivity
measurements ............................. 341
6.2 Measurements of the Hydrate Phase ........................ 342
6.2.1 Mesoscopic Measurements of the Hydrate Phase ...... 342
6.2.2 Molecular-Level Measurements of the Hydrate
Phase ............................................. 346
6.2.2.1 Diffraction methods ...................... 349
6.2.2.2 Spectroscopic methods .................... 350
6.3 Data for Natural Gas Hydrate Phase Equilibria and
Thermal Properties ....................................... 358
6.3.1 Phase Equilibria Data ............................. 358
6.3.1.1 Equilibria of simple natural gas
components ............................... 358
6.3.1.2 Equilibria of binary guest mixtures ...... 392
6.3.1.3 Equilibria of ternary guest mixtures ..... 440
6.3.1.4 Equilibria of multicomponent guest
mixtures ................................. 448
6.3.1.5 Equilibria with inhibitors ............... 461
6.3.2 Thermal Property Data ............................. 519
6.3.2.1 Heat capacity and heat of dissociation ... 519
6.4 Summary and Relationship to Chapters that Follow ......... 523
References ............................................... 523
Chapter 7 Hydrates in the Earth .............................. 537
Introduction and Overview ..................................... 537
7.1 The Paradigm Is Changing from Assessment of Amount to
Production of Gas ........................................ 539
7.1.1 Extent of the Occurrence of In Situ Gas Hydrates .. 539
7.2 Sediments with Hydrates Typically Have Low Contents of
Biogenic Methane ......................................... 550
7.2.1 Generation of Gases for Hydrate Formation ......... 551
7.2.2 The SMI, the Hydrate Upper Boundary, and the SMI
Rule-of-Ten ....................................... 555
7.2.3 Mechanisms for Generation of Hydrates ............. 557
7.2.3.1 Hydrate formation in the two-phase
region ................................... 558
7.2.3.2 Models for in situ hydrate formation ..... 560
7.3 Sediment Lithology and Fluid Flow Are Major Controls on
Hydrate Deposition ....................................... 566
7.4 Remote Methods Enable an Estimation of the Extent of
a Hydrated Reservoir ..................................... 566
7.4.1 The Hydrate Pressure-Temperature Stability
Envelope .......................................... 567
7.4.2 Seismic Velocity Techniques and Bottom
Simulating Reflections ............................ 571
7.4.3 Methane Solubility Further Limits the Hydrate
Occurrence ........................................ 575
7.5 Drilling Logs and/Coring Provide Improved Assessments
of Hydrated Gas Amounts .................................. 576
7.5.1 Open Hole Well Logs ............................... 577
7.5.2 Evidence of Hydrates in Cores ..................... 578
7.5.3 Combining Laboratory and Field Experiments ........ 582
7.6 Hydrate Reservoir Models Indicate Key Variables for
Methane Production ....................................... 583
7.7 Future Hydrated Gas Production Trends Are from the
Permafrost to the Ocean .................................. 587
7.8 Hydrates Play a Part in Climate Change and Geohazards .... 589
7.8.1 Case Study 1: Leg 164 in the Blake-Bahama Ridge
(Hydrate Assessment) .............................. 592
7.8.1.1 Site 994 ................................. 594
7.8.1.2 Site 995 ................................. 597
7.8.1.3 Site 997 ................................. 598
7.8.1.4 Common features .......................... 598
7.8.2 Case Study 2: Hydrate Ridge (Hydrate Assessment) .. 599
7.8.2.1 Near surface hydrates: the
chemosynthetic community and chemoherms .. 601
7.8.2.2 Deeper hydrates at Southern Hydrate
Ridge: characterization and assessment ... 604
7.8.2.3 Logs and remote sensing .................. 605
7.8.2.4 Coring and direct evidence ............... 607
7.8.2.5 The lessons of Hydrate Ridge ............. 608
7.8.3 Case Study 3: Messoyakha (Hydrate Production
in Permafrost) .................................... 609
7.8.4 Case Study 4: Mallik 2002 (Hydrate Production
in Permafrost) .................................... 616
7.8.4.1 Background of the Mallik 2002 well ....... 617
7.8.4.2 Overview of the Mallik 2002 well ......... 618
7.8.4.3 Well logs in Mallik 2002 ................. 620
7.8.4.4 Pressure stimulation tests in the 5L-38
well ..................................... 620
7.8.4.5 The Thermal stimulation test in Mallik
5L-38 .................................... 621
7.8.4.6 Modeling gas production from hydrates .... 625
7.9 Summary ............................................. 628
References ............................................... 629
Chapter 8 Hydrates in Production, Processing, and
Transportation ................................................ 643
Introduction .................................................. 644
8.1 How Do Hydrate Plugs Form in Industrial Equipment? ....... 644
8.1.1 Case Study 1: Hydrate Prevention in a Deepwater
Gas Pipeline ...................................... 645
8.1.2 Case Study 2: Hydrates Prevention via
Combination of Methods ............................ 647
8.1.2.1 Burying the pipeline ..................... 648
8.1.2.2 Line burial with wellhead heat addition .. 649
8.1.2.3 Burial, heat addition, and insulation .... 649
8.1.2.4 Methanol addition alternative ............ 650
8.1.3 Case Study 3: Hydrate Formation via Expansion
through Valves or Restrictions .................... 651
8.1.4 Conceptual Overview: Hydrate Plug Formation in
Oil-Dominated Systems ............................. 653
8.1.5 Conceptual Overview: Hydrate Formation in Gas-
Dominated Systems ................................. 654
8.2 How Are Hydrate Plug Formations Prevented? ............... 656
8.2.1 Case Study 4: Thermodynamic Inhibition Canyon
Express and Ormen Lange Flowlines ................. 656
8.2.2 Case Study 5: Under-Inhibition by Methanol in
a Gas Line ........................................ 658
8.2.3 Kinetic Hydrate Inhibition ........................ 659
8.2.3.1 Antiagglomerant means of preventing
hydrate plugs ............................ 662
8.2.4 Case Study 6: AAs are a Major Hydrate Plug
Prevention Tool ................................... 668
8.3 How Is a Hydrate Plug Dissociated? ....................... 669
8.3.1 Case Study 7: Gulf of Mexico Plug Removal in
Gas Export Line ................................... 675
8.4 Safety and Hydrate Plug Removal .......................... 676
8.4.1 Case Study 8: Hydrate Plug Incident Resulting in
Loss of Life ...................................... 677
8.5 Applications to Gas Transport and Storage ................ 678
8.6 Summary of Hydrates in Flow Assurance and
Transportation ........................................... 679
References ............................................... 679
Appendix A CSMGem Example Problems ........................... 685
A.l Introduction ........................................ 685
A.2 Example Problems .................................... 686
A.3 Setting up the Natural Gas Example .................. 686
A.4 Incipient Hydrate Formation Conditions .............. 686
A.5 Plotting a 2-Phase VLE Curve ........................ 688
A.6 Adding Hydrate Inhibitor ............................ 688
A.7 Adding Hydrate Inhibitor Solutions .................. 690
А.8 Expansion Across a Valve ............................ 690
А.9 Expansion Across a Valve Solutions .................. 691
A.10 Real Life Situation ................................. 691
Appendix В CSMPlug Example Problems .......................... 693
B.l Introduction ........................................ 693
B.2 Example Problem for One-Sided Dissociation .......... 693
B.3 1SD Solutions ....................................... 694
B.4 Example Problem for Two-Sided Dissociation .......... 695
B.5 2SD Solution ........................................ 697
B.6 Example Problem for Safety Simulator ................ 697
B.7 Safety Simulator Solutions .......................... 698
B.8 Example Problem for Electrical Heating .............. 699
B.9 Electrical Heating Solutions ........................ 699
Index ......................................................... 703
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