Exploration of Gas Hydrates (eBook)

Exploration of Gas Hydrates 3
Preface 5
Contents 7
Chapter 1: Introduction 11
1.1 Introduction 11
1.2 Oil and Natural Gas 14
1.3 Coal Energy 18
1.3.1 Coal Gasification 19
1.3.2 Coal Liquefaction 20
1.3.3 Coal Bed Methane 20
1.4 Geothermal Energy 21
1.5 Nuclear Energy 24
1.6 Nuclear Fusion 26
1.7 Renewable Energy 27
1.7.1 Hydropower 27
1.7.2 Solar Energy 29
1.7.3 Bio-Energy 31
1.7.4 Wind Energy 32
1.7.5 Tidal Energy 34
1.7.6 Wave Energy 35
References 37
Chapter 2: World´s Oil and Natural Gas Scenario 38
2.1 Introduction 38
2.2 Oil Scenarios 42
2.3 Natural Gas 46
2.3.1 Natural Gas Scenario 48
2.4 Unconventional Oil 50
2.4.1 Shale Oil 52
2.5 Unconventional Gas 52
2.5.1 Tight Sands 53
2.5.2 Shale Gas 53
2.5.3 Geopressured Zones 53
2.6 Hydrogen 54
References 55
Chapter 3: Gas Hydrates 57
3.1 Introduction 57
3.2 What Are Gas Hydrates? 58
3.3 Crystal Structure 60
3.4 Where Gas Hydrates Are Found? 62
3.5 Gas Hydrates Indicators 67
3.5.1 Geophysical Signatures 67
3.5.2 Geological Proxies 69
3.5.3 Geochemical Evidences 70
3.5.4 In-Situ Measurements 71
3.6 Possible Resource Estimates 74
References 76
Chapter 4: Stability Conditions 81
4.1 Introduction 81
4.2 Availability of Methane 82
4.3 Pressure-Temperature Conditions 83
4.3.1 Hydrostatic Pressure 84
4.3.2 Hydrothermal Gradients 84
4.3.3 Geothermal Gradients 85
4.4 Gas Hydrate Stability Zone 86
4.4.1 Salinity 88
4.4.2 Gas Composition 89
4.4.3 Solubility of Methane 92
4.4.4 Geological Controls 93
4.5 Planetary Hydrates 95
4.6 Climatic Impact 95
4.7 Geological Hazards 99
References 101
Chapter 5: Geological Indicators 106
5.1 Introduction 106
5.2 Geological Indicators 107
5.2.1 Distribution and Variability of BSR 109
5.2.1.1 Ridge-Type BSR 109
Class I: BSRs in Anticlinal Ridge Structures 109
Class II: BSRs in Buried-Anticline Structures 109
Class III: BSRs in Thrusted-Ridge Structures 112
Class IV: BSRs in Thrusted-Footwall Structures 112
5.2.1.2 Basin-Type BSR 114
5.2.1.3 Submarine-Canyon Type BSR 114
5.2.1.4 Continental Slope Type BSR 118
5.2.2 Sediment Deposition and Distribution 119
5.2.3 Diapirism 126
5.2.4 Fluid Migration Features 127
5.2.4.1 Pockmarks 129
5.2.4.2 Mud Volcanoes 129
5.2.4.3 Faulting 131
References 132
Chapter 6: Geophysical Indicators 136
6.1 Introduction 136
6.2 Geophysical Indicators 137
6.2.1 The Bottom Simulating Reflectors 138
6.2.2 Enhanced Seismic Reflections Below BSR 138
6.2.3 Seismic Chimney and Amplitude Blanking 139
6.2.4 Hydrate Mounds 140
6.2.5 Instantaneous Seismic Attributes 144
6.2.5.1 Reflection Strength 144
6.2.5.2 Instantaneous Frequency 144
References 146
Chapter 7: Geophysical Surveys and Data Analysis 149
7.1 Introduction 149
7.2 2D/3D Conventional Seismic Surveys 151
7.3 4C Ocean Bottom Seismic Surveys 153
7.3.1 Patterns in Travel Time for Ocean Bottom Seismometer Experiments 155
7.3.2 Example of 4C Seismic Experiment 158
7.4 Vertical Seismic Profile Surveys 162
7.4.1 The Beginning Point: Zero Offset VSP 163
7.4.2 Walk-Away VSP 165
7.4.3 Cross-Well Seismic Surveys (CSP) 167
7.4.4 Some Remarks 170
7.5 Marine Controlled-Source Electromagnetic Methods (CSEM) 171
7.6 Seismic Data Analysis for Gas Hydrate Characterization 177
7.6.1 Patterns in Synthetic Seismograms for Gas Hydrates 180
7.6.1.1 Patterns in Synthetic Seismogram for Simple Multilayered Gas Hydrate and Free Gas Model 182
7.6.1.2 Patterns in Synthetic Seismograms for Models Having Brine Saturated Sand Layer Between Gas Hydrates and Free Gas Bearin 185
7.6.1.3 Converted Waves patterns for Complex Bottom Simulating Reflector Model 190
Some Remarks 196
7.6.2 Converted Wave Velocity Model for Gas Hydrate Studies 197
7.6.2.1 Geologic Settings of Hydrate Ridge 197
7.6.2.2 Velocity Analysis 198
Some Remarks 202
7.6.3 Processing of 4C OBS Data for Gas Hydrate Studies 203
7.7 Log Responses for Gas Hydrates 203
7.7.1 Electrical Resistivity Log Response 204
7.7.2 Spontaneous Potential Log Response 205
7.7.3 Caliper Log Response 206
7.7.4 Sonic Log Response 208
7.7.5 Neutron Log Response 209
7.7.6 Density Log Response 210
7.7.7 Some Remarks 210
References 211
Chapter 8: Identification to Quantification of Gas Hydrates 216
8.1 Introduction 216
8.2 Regional Mapping of Gas Hydrates 218
8.2.1 An Example from Kerala-Konkan (KK) Basin Offshore India 219
8.2.2 Some Remarks 222
8.3 Amplitude Strength 226
8.3.1 Some Remarks 229
8.4 Amplitude vs. Offset Characteristics 230
8.4.1 Calculation of Synthetic Seismogram and Reflection Coefficient 231
8.4.2 Some Remarks 235
8.5 Seismic Attributes 236
8.5.1 Reflection Strength 237
8.5.2 Reflection Strength for Constant Thickness of Hydrate Layer with Different Thickness of Free Gas Layers 237
8.5.3 Reflection Strength for Constant Thickness of Free Gas Layer with Different Thickness of Gas Hydrate Layers 239
8.5.4 Example from Andaman Offshore Region, India 240
8.5.5 Example from Offshore Australia 241
8.5.6 Instantaneous Frequency 243
8.5.7 Instantaneous Frequency for Constant Thickness of Hydrate Layer with Different Thickness of Free Gas Layers 247
8.5.8 Instantaneous Frequency for Constant Thickness of Free Gas Layer with Different Thickness of Gas Hydrate Layers 247
8.5.9 Example from Andaman Offshore Region, India 247
8.5.10 Example from Offshore Australia 248
8.5.11 Some Remarks 250
8.6 Quantification Methods 250
8.6.1 Detection and Estimation of Gas Hydrates by Rock Physics and Inversion 251
8.6.2 Estimating Volumetric Concentration of Gas Hydrates by Modified Wood Equation 254
8.6.3 Example from KG Basin India (NGHP Expedition-01) 259
8.6.4 Integrating Geochemical and Geophysical Methods for Gas Hydrates Characterization 260
8.6.5 Waveform Inversion for Gas Hydrates 262
References 264
Chapter 9: The Road Ahead 270
9.1 Introduction 271
9.2 Stability 271
9.3 Bottom Simulating Reflector 273
9.4 Blanking 275
9.5 Inferences from Velocities 276
9.6 AVO Modeling 277
9.7 Seismic Data Acquisition 278
References 279
Index 282