Experiments Concerning the Commerical Extraction of Methane Fr
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EXPERIMENTS CONCERNING THE COMMERCIAL EXTRACTION OF METHANE FROM COALBED RESERVOIRS by Ian Morton Loomis Dissertation submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Mining Engineering Approved: Dr. Malcolm McPherson Dr. Michael Karmis Dr. Gerald Luttrell Dr. Ertugrul Topuz Dr. Mark Widdowson April 1997 Blacksburg, Virginia Keywords: Methane Drainage, Natural Gas, Coal, Tailored Pulse, Propellant EXPERIMENTS CONCERNING THE COMMERCIAL EXTRACTION OF METHANE FROM COALBED RESERVOIRS by Ian Morton Loomis Malcolm J. McPherson, Chairman Department of Mining and Minerals Engineering (ABSTRACT) In late 1992 coalbed methane became the most significant source of natural gas produced in Virginia. This gas is held within the coal formations adsorbed to the coal matrix. The current well stimulation technology applies a high pressure fluid to the coal formation surrounding the wellbore to induce a series of fractures. The research documented in this thesis investigates several new technologies that could replace or augment the current well stimulation approach of hydraulic fracturing. The application of liquid carbon dioxide, as the stimulation agent was investigated in a series of permeability tests. These measurements were made using a radial flow technique developed specifically for this research project. The results of the tests using liquid carbon dioxide to enhance the permeability of coal samples, to methane gas, indicated a significant increase in permeability of the samples. Comparison to a reference material showed, however, that the increase was of a general nature, not by specific interaction with the coal matrix. Rather, the permeability increase was due to reduced resistance of the borehole skin. Studies of the new, radial flow, permeability measurement approach showed good agreement to a conventional, axial flow, approach for similar sample bedding orientation to the gas flow. The documented experiments also include investigations into the potential for using custom designed nitrocellulose/nitroglycerin/RDX based propellant charges to produce extensive fracturing away from the wellbore. The first series of these experiments concerned the characterization of the burn properties for these propellants and their mixtures. Utilizing an interior ballistics approach, these laboratory small-scale shots were numerically modeled with a program written as a part of this project. Using the small-scale results and the modeled data, a series of large-scale test shots were developed and fired to gain understanding of the scale effects. The small-scale constant volume bomb, and the large-scale vented bomb were both custom designed and fabricated for this project. Comparisons of the laboratory data and modeled predictions show good agreement for both the small and large-scale test series. This work concludes by presenting considerations for utilizing the propellant based well stimulation approach in the water filled wells in southwest Virginia. ACKNOWLEDGMENTS I wish to thank Professor Malcolm McPherson, my academic advisor and committee chairman for his guidance during the course of this work. I wish to thank, also, the members of my review committee, Professors Michael Karmis, Gerald Luttrell, Ertugrul Topuz, and Mark Widdowson. Many thanks are extended to Mr. Wayne Slusser whose efforts in the Mining and Minerals Engineering machine shop are greatly appreciated. Recognition for funding of this research is extended to Virginia’s Center for Innovative Technology, the Pittston Coal Company, Pine Mountain Oil and Gas, Inc., and Equitable Resources, Inc. Final thanks go to my parents, David and Evelyn. iii Table of Contents Chapter Description Page Cover i Abstract ii Acknowledgments iii Table of Contents v List of Tables xii List of Figures xiii List of Plates xix Lexicon xxii 1 Introduction 1 1.1 State of Affairs 1 1.2 Existing Technology 5 1.3 Current Investigations 7 2 Literature Review 9 2.1 Nature of the Problem 10 2.1.1 Unconventional Methane Sources 10 2.1.2 Distribution of Coalbed Methane 12 2.1.2.1 Throughout the United States 12 2.1.2.2 Within Virginia 13 2.1.3 Economic Assessment 14 2.2 State of the Art 15 2.2.1 Open Hole-Stable Cavity Completions 15 2.2.2 Cased Hole Completions 19 2.2.2.1 Cross-Linked Gels 20 2.2.2.2 Water Fracturing 20 2.2.2.3 Foam Fracturing 21 2.2.3 Effect of Permeability 21 2.2.3.1 Methane Desorption Characteristics 22 2.2.3.2 Diffusion of Methane in Coal Matrix 25 2.2.3.3 Movement of Methane in Cleats and Fractures 25 iv Chapter Description Page 2.2.3.4 Effect of Relative Permeability and Two-Phase Flow 26 2.2.3.5 Permeability Assessment 27 2.2.3.5.1 Field Methods 27 2.2.3.5.2 Laboratory Methods 32 2.2.3.6 Coal Swelling 33 2.3 Advanced Techniques in Well Stimulation 34 2.3.1 Multiple Fracturing (Tailored Pulse) 34 2.2.3 Liquid Carbon Dioxide 38 2.4 Performance Assessment 39 2.5 Methane Production Simulation 40 3 Tests Involving Liquid Carbon Dioxide 42 3.1 Basic Theory 42 3.1.1 Permeability Measurement 47 3.1.1.1 Axial Samples 47 3.1.1.2 Radial Samples 48 3.1.1.3 Conditions of Flow and Pressure Effects 49 3.1.1.3.1 Reynold’s Number Criteria 49 3.1.1.3.2 Pressure Effects on Viscosity 50 3.1.1.3.3 Porous Media Parameters 51 3.1.2 Approach to Laboratory Measurement of Radial Permeability 52 3.1.3 Baseline Procedure for Comparison Between Axial and Radial 53 Measurements 3.1.4 Comparison of Mean Pressure and Pressure Gradient in 53 Baseline Samples 3.1.5 Effects of Carbon Dioxide on Coal 58 3.1.6 Effects of Pressure State of the Sample 61 3.2 Test Procedure and Parameters 62 3.2.1 Sample Preparation 65 3.2.2 Test Cell Configuration 77 3.2.3 Data Collection 80 3.2.3.1 Manual Data Collection 80 3.2.3.2 Automatic Data Collection 80 3.2.4 Evaluation 81 3.2.4.1 Sandstone Samples 81 3.2.4.2 Coal Samples 82 3.2.5 Possible Patent Information 83 v Chapter Description Page 3.3 Results 85 3.3.1 Baseline Samples 85 3.3.1.1 Axial Samples 88 3.3.1.1.1 Sample SSAXI1 88 3.3.1.1.2 Sample SSAXI2 91 3.3.1.1.3 Sample SSAXI3 94 3.3.1.2 Radial Samples 97 3.3.1.2.1 Sample SSRAD1 97 3.3.1.2.2 Sample SSRAD2 99 3.3.1.2.3 Sample SSRAD3 102 3.3.1.2.4 Sample SSRAD4 105 3.3.2 Coal Samples for Evaluation 109 3.3.2.1 Sample PMOGS 110 3.3.2.2 Sample PMOG01 113 3.3.2.3 Sample PMOG05 115 3.3.2.4 Sample PMOG09 119 3.3.2.5 Sample PMOG10 121 3.3.2.6 Sample PMOG11 123 3.3.2.7 Sample PMOG12 125 3.3.2.8 Sample PMOG13 127 3.3.2.9 Sample PMOG16 129 3.3.2.10 Sample PMOG17 129 3.3.3 Other Samples of Interest 132 3.3.3.1 Liquid Carbon Dioxide 132 3.3.3.2 Gaseous Carbon Dioxide 133 3.4 Discussion 135 3.4.1 Disking Phenomenon 135 3.4.2 Effect of Sample Make Up 135 3.4.3 Comparison of Permeability Measured in Axial and Radial 136 Samples 3.4.4 Parametric Effects 137 3.4.4.1 Effect of Variation of Temperature 141 3.4.4.2 Effect of Variation of Mean Gas Pressure 141 3.4.4.3 Effect of Variation of Mass Flow Rate 142 3.4.5 Effect of Liquid Carbon Dioxide Treatment 143 3.4.6 Effect of the Radial Flow Sample Design 146 3.4.7 Potential for Carbon Dioxide in Coalbed Methane Stimulation 147 3.5 Nomenclature 151 vi Chapter Description Page 4 Tests of Propellant Characterization 153 4.1 Basic Theory 153 4.1.1 Confined Fracturing Fundamentals 154 4.1.2 Hydraulic Fracturing 159 4.1.3 Fracturing with High Explosives 159 4.1.4 Propellant Fracturing 161 4.2 Apparatus and Test Parameters 165 4.2.1 Propellant Properties 166 4.2.2 Confined Tests 168 4.2.2.1 Pressure Vessel 168 4.2.2.2 Charge Design 170 4.2.2.3 Data Logging System 171 4.2.3 Test Assembly 173 4.2.4 Data Evaluation 182 4.3 Results 182 4.3.1 Commercial Propellant Particle Size Distribution 182 4.3.2 Confined Burning Tests 190 4.3.2.1 100 Percent No. 5 197 4.3.2.2 75 Percent No. 5, 25 Percent No. 8700 204 4.3.2.3 66 Percent No. 5, 34 Percent No. 8700 209 4.3.2.4 50 Percent No. 5, 50 Percent No. 8700 213 4.3.2.5 100 Percent No. 8700 216 4.3.2.6 75 Percent No. 5, 25 Percent Model Rocket Fuel 216 4.3.2.7 66 Percent No. 5, 34 Percent Model Rocket Fuel 216 4.3.2.8 50 Percent No. 5, 50 Percent Model Rocket Fuel 216 4.3.2.9 100 Percent Model Rocket Fuel 222 4.3.2.10 100 Percent No. 2 - Improved 225 4.3.2.11 100 Percent Commercial Black Powder 230 4.4 Determination of Linear Burn Rates 237 4.4.1 100 Percent No. 5 242 4.4.2 75 Percent No. 5, 25 Percent No. 8700 251 4.4.3 66 Percent No. 5, 34 Percent No. 8700 257 4.4.4 50 Percent No.