Chapter 1 - Introduction
1.0. Introduction ............................................... 1
1.1. U.S. Clean Energy Needs .................................... 3
1.2. Future Role of Natural Gas ................................. 7
1.3. The Conventional Natural Gas Resource ...................... 9
1.4. The Coal Resource ......................................... 12
1.5. The CBM Resource .......................................... 14
1.6. Overview: CBM vs. Conventional Reservoir .................. 19
1.6.1. Gas Composition .................................... 19
1.6.2. Adsorption ......................................... 20
1.6.3. Water Production ................................... 21
1.6.4. Gas Flow ........................................... 22
1.6.5. Rock Physical Properties ........................... 22
1.6.6. Gas Content ........................................ 23
1.6.7. Coal Rank .......................................... 24
1.6.8. Gas Production ..................................... 25
1.7. СН4 Potential of Major U.S. Coal Basins ................... 25
1.7.1. San Juan Basin ..................................... 28
1.7.2. Black Warrior Basin ................................ 33
1.7.3. Raton Basin ........................................ 38
1.7.4. Piceance Basin ..................................... 41
1.7.5. Greater Green River Coal Region .................... 44
1.7.6. Powder River Basin ................................. 48
1.7.7. Northern Appalachian Basin ......................... 51
1.7.8. Central Appalachian Basin .......................... 54
1.7.9. Western Washington ................................. 56
1.7.10.Wind River Basin ................................... 57
1.7.11.Illinois Basin ..................................... 59
1.7.12.Arkoma Basin ....................................... 61
1.7.13.Uinta Basin ........................................ 63
1.7.14.Cherokee Basin ..................................... 64
Chapter 2 - Geological Influences on Coal
2.1. Formation of Coals ........................................ 77
2.1.1. Stratigraphic Periods .............................. 78
2.1.2. Tertiary Coals of Western United States ............ 78
2.1.3. Cretaceous Coals of Western United States .......... 79
2.1.4. Carboniferous Coals of Eastern United States ....... 83
2.1.5. Influence of Coal Properties ....................... 84
2.1.6. AGenesis Model of Coal ............................. 84
2.1.7. Geochemical Transformation ......................... 86
2.2. Coal Chemistry ............................................ 91
2.2.1. Molecular Structure ................................ 91
2.2.2. Macerals ........................................... 96
2.2.3. Lithotypes ......................................... 99
2.2.4. Functional Groups ................................. 101
2.2.5. Proximate Analysis ................................ 103
2.2.6. Ultimate Analysis ................................. 108
2.3. Significance of Rank ..................................... 108
2.3.1. Definition and Measurement ........................ 109
2.3.2. Vitrinite Reflectance Measurement ................. 114
2.3.3. Physical Properties ............................... 116
2.3.4. Volatiles Generated ............................... 125
2.3.5. Micropores ........................................ 126
2.4. Cleat System and Natural Fracturing ...................... 128
Chapter 3 - Sorption
3.1. Principles of Adsorption ................................. 143
3.1.1. Theory Overview ................................... 143
3.1.2. Langmuir Isotherm ................................. 145
3.1.3. Similarities of Adsorbed Methane and Liquid
Behavior .......................................... 151
3.1.4. Extended Langmuir Isotherm ........................ 156
3.1.5. Industry Uses of Adsorbents ....................... 159
3.2. The Isotherm Construction ................................ 160
3.3. СШ Retention by Coalseams ................................ 165
3.4. Cm Content Determination in Coalseams .................... 169
3.5. The Isotherm for Recovery Prediction ..................... 174
3.6. Model of the Micropores .................................. 176
3.6.1. Pore Geometry ..................................... 176
3.6.2. Carbon Molecular Sieves ........................... 177
3.7. Coal Sorption of Other Molecular Species ................. 179
3.7.1. Swelling of Coal Matrix ........................... 179
3.7.2. Heavier Hydrocarbons .............................. 179
3.7.3. Carbon Dioxide and Nitrogen ....................... 182
3.8. Effects of Ash and Moisture on CH4 Adsorption ............ 183
Chapter 4 - Reservoir Analysis
4.1. Coal as a Reservoir ...................................... 191
4.2. Permeability ............................................. 193
4.2.1. Drillstem Test (DST) .............................. 197
4.2.2. Slug Test ......................................... 198
4.2.3. Injection Falloff Tests ........................... 204
4.2.4. Depth Effects on Permeability ..................... 214
4.2.5. Klinkenberg, Shrinkage, and Stress Effects
on Permeability ................................... 217
4.2.6. Water Composition as Permeability Indicator ....... 224
4.2.7. Relative Permeability ............................. 224
4.2.8. Butt and Cleat Permeabilities ..................... 227
4.3. Porosity ................................................. 231
4.4. Gas Flow ................................................. 232
4.4.1. Diffusion in Micropores ........................... 232
4.4.2. Darcy Flow in Cleats .............................. 239
4.4.3. Sorption Time ..................................... 242
4.5. Reserve Analysis ......................................... 247
4.5.1. Gas in Place ...................................... 247
4.5.2. Decline Curves .................................... 258
4.6. Well Spacing and Drainage Area ........................... 265
4.7. Enhanced Recovery ........................................ 268
Chapter 5 - Well Construction
5.1. Drilling ................................................. 283
5.1.1. Drill Bits ........................................ 284
5.1.2. Drilling Fluids ................................... 284
5.2. Cementing ................................................ 285
5.2.1. Foam Cement ....................................... 286
5.2.2. Lightweight Additives ............................. 287
Chapter 6 - Formation Evaluations, Logging
6.1. Introduction ............................................. 289
6.2. Borehole Environment ..................................... 290
6.2.1. Downhole Environment .............................. 290
6.2.2. Wireline Logging .................................. 291
6.3. Tool Measurement Response in Coal ........................ 294
6.3.1. Natural Gamma Ray ................................. 294
6.3.2. Spontaneous Potential ............................. 297
6.3.3. Resistivity Measurements .......................... 297
6.3.4. Micro-Resistivity Measurements .................... 300
6.3.5. Nuclear Measurements .............................. 304
6.3.6. Acoustic Measurements ............................. 309
6.3.7. Magnetic Resonance Measurements ................... 310
6.3.8. Electrical Imaging ................................ 311
6.4. Wireline Log Evaluation of CBM Wells ..................... 314
6.4.1. Coal Identification ............................... 314
6.4.2. Coal Tonnage ...................................... 315
6.4.3. Proximate Analysis ................................ 315
6.4.4. Gas Content in Coal ............................... 316
6.5. Gas-ln-Place Calculations ................................ 317
6.6. Recovery Factor .......................................... 317
6.7. Drainage Area Calculations ............................... 318
6.8. Coal Permeability/Cleating ............................... 318
6.9. Natural Fracturing and Stress Orientation ................ 319
6.10.Mechanical Rock Properties in CBM Evaluation ............. 320
6.11.Summary .................................................. 320
Chapter 7 - Completions
7.1. Introduction ............................................. 323
7.2. Openhole Completions ..................................... 323
7.3. Openhole Cavitation Process .............................. 326
7.3.1. Introduction ...................................... 326
7.3.2. Case Study: Cavitation Research Project ........... 328
7.3.3. Case Study: Devon Cavity Process .................. 332
7.4. Cased-Hole Completions ................................... 335
7.4.1. Conditions for Cased Hole ......................... 335
7.4.2. Access by Slotting ................................ 336
7.4.3. Access by Perforating ............................. 339
7.5. Multizone Entry in Cased Hole ............................ 340
7.5.1. Baffled Entry ..................................... 340
7.5.2. Frac Plug Entry ................................... 343
7.5.3. Partings Entry .................................... 344
7.5.4. Coiled Tubing and Packer Completions .............. 348
Chapter 8 - Hydraulic Fracturing of Coalseams
8.1. Need for Fracturing Coals ................................ 357
8.1.1. Appalachian Wells Inadequately Stimulated ......... 358
8.1.2. Unstimulated Wells in Big Run Field ............... 362
8.2. Unique Problems in Fracturing Coals ...................... 363
8.2.1. Fines ............................................. 364
8.2.2. Fluid Damage ...................................... 369
8.2.3. Excessive Treating Pressures ...................... 373
8.2.4. Leakoff ........................................... 377
8.3. Types of Fracturing Fluids for Coal ...................... 381
8.3.1. Crosslinked Gels .................................. 382
8.3.2. Water ............................................. 388
8.3.3. Comparison of Gel and Water ....................... 390
8.3.4. Foam .............................................. 392
8.3.5. Proppant Considerations ........................... 394
8.4. In-Situ Conditions ....................................... 397
8.4.1. Rock Properties ................................... 397
8.4.2. Stress ............................................ 402
8.4.3. Determining Stress Values ......................... 409
8.5. Visual Observation of Fractures .......................... 411
Chapter 9 - Water Production and Disposal
9.1. Introduction ............................................. 421
9.2. Water Production Rates from Methane Wells ................ 423
9.2.1. Initial Water Production Rates .................... 423
9.2.2. Water Decline Rates ............................... 425
9.2.3. Anomalous Water Production Rates .................. 426
9.3. Chemical Content ......................................... 427
9.4. Environmental Regulations ................................ 436
9.4.1. Toxicity Limitations of Coalbed Water ............. 436
9.4.2. Regulatory Agencies of the Warrior Basin .......... 440
9.4.3. Regulatory Agencies of the San Juan Basin ......... 441
9.5. Water Disposal Techniques ................................ 443
9.5.1. Surface-Stream Disposal ........................... 443
9.5.2. Injection Wells ................................... 453
9.6. Summary .................................................. 455
Chapter 10 - Economics of Coalbed Methane Recovery
10.0.Introduction ............................................. 461
10.1.Tax Credit ............................................... 462
10.1.1.History of the Credit ............................. 462
10.2.Measures of Profitability ................................ 463
10.2.1.Criteria for Economical Methane Project ........... 463
10.2.2.Comparison of Measures of Profitability ........... 467
10.3.Costs .................................................... 470
10.3.1.Drilling and Completion ........................... 470
10.3.2.Water Disposal .................................... 474
10.3.3.Finding Costs ..................................... 477
10.4.Structured Resource Evaluation ........................... 478
10.4.1.Gas Content Sensitivity ........................... 479
10.4.2.Permeability Sensitivity .......................... 481
10.4.3.Spacing Sensitivity ............................... 482
10.4.4.Permeability Anisotropy Sensitivity ............... 484
10.4.5.Fracture Length Sensitivity ....................... 487
Acronyms ...................................................... 491
Index ......................................................... 495
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