Contents

Chapter 1—Introduction1.0 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 ....................................... 191.6.1 Gas Composition .................................................................... 191.6.2 Adsorption ............................................................................... 201.6.3 Water Production .................................................................... 211.6.4 Gas Flow ................................................................................. 221.6.5 Rock Physical Properties ........................................................ 221.6.6 Gas Content ............................................................................ 231.6.7 Coal Rank ............................................................................... 241.6.8 Gas Production ....................................................................... 25

1.7 CH4 Potential of Major U.S. Coal Basins ............................................ 251.7.1 San Juan Basin ....................................................................... 281.7.2 Black Warrior Basin ................................................................ 331.7.3 Raton Basin ............................................................................ 381.7.4 Piceance Basin ....................................................................... 411.7.5 Greater Green River Coal Region ........................................... 441.7.6 Powder River Basin ................................................................ 481.7.7 Northern Appalachian Basin ................................................... 511.7.8 Central Appalachian Basin ...................................................... 541.7.9 Western Washington ............................................................... 561.7.10 Wind River Basin .................................................................... 571.7.11 Illinois Basin ............................................................................ 591.7.12 Arkoma Basin .......................................................................... 611.7.13 Uinta Basin .............................................................................. 631.7.14 Cherokee Basin ...................................................................... 64

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Chapter 2—Geological Influences on Coal2.1 Formation of Coals .............................................................................. 77

2.1.1 Stratigraphic Periods ............................................................... 782.1.2 Tertiary Coals of Western United States ................................. 782.1.3 Cretaceous Coals of Western United States .......................... 792.1.4 Carboniferous Coals of Eastern United States ....................... 832.1.5 Influence of Coal Properties .................................................... 842.1.6 A Genesis Model of Coal ........................................................ 842.1.7 Geochemical Transformation .................................................. 86

2.2 Coal Chemistry .................................................................................... 912.2.1 Molecular Structure ................................................................. 912.2.2 Macerals ................................................................................. 962.2.3 Lithotypes ................................................................................ 992.2.4 Functional Groups ................................................................... 1012.2.5 Proximate Analysis ................................................................. 1032.2.6 Ultimate Analysis .................................................................... 108

2.3 Significance of Rank ........................................................................... 1082.3.1 Definition and Measurement ................................................... 1092.3.2 Vitrinite Reflectance Measurement ......................................... 1142.3.3 Physical Properties ................................................................. 1162.3.4 Volatiles Generated ................................................................ 1252.3.5 Micropores .............................................................................. 126

2.4 Cleat System and Natural Fracturing .................................................. 128

Chapter 3—Sorption3.1 Principles of Adsorption ...................................................................... 143

3.1.1 Theory Overview ..................................................................... 1433.1.2 Langmuir Isotherm .................................................................. 1453.1.3 Similarities of Adsorbed Methane and Liquid Behavior .......... 1513.1.4 Extended Langmuir Isotherm .................................................. 1563.1.5 Industry Uses of Adsorbents ................................................... 159

3.2 The Isotherm Construction .................................................................. 160

3.3 CH4 Retention by Coalseams ............................................................. 165

3.4 CH4 Content Determination in Coalseams .......................................... 169

3.5 The Isotherm for Recovery Prediction ................................................. 174

3.6 Model of the Micropores ...................................................................... 1763.6.1 Pore Geometry ........................................................................ 1763.6.2 Carbon Molecular Sieves ........................................................ 177

Contents

3.7 Coal Sorption of Other Molecular Species .......................................... 1793.7.1 Swelling of Coal Matrix ............................................................ 1793.7.2 Heavier Hydrocarbons ............................................................. 1793.7.3 Carbon Dioxide and Nitrogen .................................................. 182

3.8 Effects of Ash and Moisture on Ch4 Adsorption .................................. 183

Chapter 4—Reservoir Analysis4.1 Coal as a Reservoir ............................................................................. 191

4.2 Permeability ......................................................................................... 1934.2.1 Drillstem Test (DST) ............................................................... 1974.2.2 Slug Test ................................................................................. 1984.2.3 Injection Falloff Tests .............................................................. 2044.2.4 Depth Effects on Permeability ................................................. 2144.2.5 Klinkenberg, Shrinkage, and Stress Effects on Permeability .. 2174.2.6 Water Composition as Permeability Indicator ......................... 2244.2.7 Relative Permeability ............................................................... 2244.2.8 Butt and Cleat Permeabilities .................................................. 227

4.3 Porosity ................................................................................................ 231

4.4 Gas Flow ............................................................................................. 2324.4.1 Diffusion in Micropores ............................................................ 2324.4.2 Darcy Flow in Cleats ............................................................... 2394.4.3 Sorption Time .......................................................................... 242

4.5 Reserve Analysis ................................................................................. 2474.5.1 Gas In Place .............................................................................. 2474.5.2 Decline Curves .......................................................................... 258

4.6 Well Spacing and Drainage Area ........................................................ 265

4.7 Enhanced Recovery ............................................................................ 268

Chapter 5—Well Construction5.1 Drilling .................................................................................................. 283

5.1.1 Drill Bits ................................................................................... 2845.1.2 Drilling Fluids ........................................................................... 284

5.2 Cementing ........................................................................................... 2855.2.1 Foam Cement .......................................................................... 2865.2.2 Lightweight Additives ............................................................... 287

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Chapter 6—Formation Evaluations, Logging6.1 Introduction ......................................................................................... 289

6.2 Borehole Environment ......................................................................... 2906.2.1 Downhole Environment .......................................................... 2906.2.2 Wireline Logging .................................................................... 291

6.3 Tool Measurement Response in Coal ................................................. 2946.3.1 Natural Gamma Ray ............................................................... 2946.3.2 Spontaneous Potential ............................................................ 2976.3.3 Resistivity Measurements ....................................................... 2976.3.4 Micro-Resistivity Measurements ............................................. 3006.3.5 Nuclear Measurements ........................................................... 3046.3.6 Acoustic Measurements .......................................................... 3096.3.7 Magnetic Resonance Measurements ..................................... 3106.3.8 Electrical Imaging .................................................................... 311

6.4 Wireline Log Evaluation of CBM Wells .............................................. 3146.4.1 Coal Identification ................................................................... 3146.4.2 Coal Tonnage ......................................................................... 3156.4.3 Proximate Analysis ................................................................. 3156.4.4 Gas Content in Coal ................................................................ 316

6.5 Gas-In-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—Completions7.1 Introduction ......................................................................................... 323

7.2 Openhole Completions ........................................................................ 323

7.3. Openhole Cavitation Process .............................................................. 3267.3.1 Introduction ............................................................................. 3267.3.2 Case Study: Cavitation Research Project ............................... 3287.3.3 Case Study: Devon Cavity Process ........................................ 332

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7.4 Cased-Hole Completions .................................................................... 3357.4.1 Conditions for Cased Hole ...................................................... 3357.4.2 Access by Slotting ................................................................... 3367.4.3 Access by Perforating ............................................................. 339

7.5 Multizone Entry in Cased Hole ............................................................ 3407.5.1 Baffled Entry ........................................................................... 3407.5.2 Frac Plug Entry ....................................................................... 3437.5.3 Partings Entry ......................................................................... 3447.5.4 Coiled Tubing and Packer Completions .................................. 348

Chapter 8—Hydraulic Fracturing of Coalseams8.1 Need for Fracturing Coals ................................................................... 357

8.1.1 Appalachian Wells Inadequately Stimulated ........................... 3588.1.2 Unstimulated Wells in Big Run Field ....................................... 362

8.2 Unique Problems in Fracturing Coals .................................................. 3638.2.1 Fines ....................................................................................... 3648.2.2 Fluid Damage .......................................................................... 3698.2.3 Excessive Treating Pressures ................................................ 3738.2.4 Leakoff .................................................................................... 377

8.3 Types of Fracturing Fluids for Coal ..................................................... 3818.3.1 Crosslinked Gels ..................................................................... 3828.3.2 Water ...................................................................................... 3888.3.3 Comparison of Gel and Water ................................................ 3908.3.4 Foam ....................................................................................... 3928.3.5 Proppant Considerations ........................................................ 394

8.4 In-Situ Conditions ................................................................................ 3978.4.1 Rock Properties ...................................................................... 3978.4.2 Stress ...................................................................................... 4028.4.3 Determining Stress Values ..................................................... 409

8.5 Visual Observation of Fractures .......................................................... 411

Chapter 9—Water Production and Disposal9.1 Introduction ......................................................................................... 421

9.2 Water Production Rates from Methane Wells ..................................... 4239.2.1 Initial Water Production Rates ................................................ 4239.2.2 Water Decline Rates ............................................................... 4259.2.3 Anomalous Water Production Rates ....................................... 426

9.3 Chemical Content ................................................................................ 427

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9.4 Environmental Regulations .................................................................. 4369.4.1 Toxicity Limitations of Coalbed Water ..................................... 4369.4.2 Regulatory Agencies of the Warrior Basin .............................. 4409.4.3 Regulatory Agencies of the San Juan Basin ........................... 441

9.5 Water Disposal Techniques ................................................................. 4439.5.1 Surface-Stream Disposal ........................................................ 4439.5.2 Injection Wells ......................................................................... 453

9.6 Summary ............................................................................................. 455

Chapter 10—Economics of Coalbed Methane Recovery10.0 Introduction .......................................................................................... 461

10.1 Tax Credit ............................................................................................ 46210.1.1 History of the Credit ................................................................. 462

10.2 Measures of Profitability ...................................................................... 46310.2.1 Criteria for Economical Methane Project ................................. 46310.2.2 Comparison of Measures of Profitability .................................. 467

10.3 Costs ................................................................................................... 47010.3.1 Drilling and Completion ........................................................... 47010.3.2 Water Disposal ........................................................................ 47410.3.3 Finding Costs .......................................................................... 477

10.4 Structured Resource Evaluation .......................................................... 47810.4.1 Gas Content Sensitivity ........................................................... 47910.4.2 Permeability Sensitivity ........................................................... 48110.4.3 Spacing Sensitivity .................................................................. 48210.4.4 Permeability Anisotropy Sensitivity ......................................... 48410.4.5 Fracture Length Sensitivity ...................................................... 487

Acronyms ..................................................................................................... 491

Index ............................................................................................................ 495