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Unformatted text preview: University of Wollongong Thesis Collections University of Wollongong Thesis Collection University of Wollongong Year Improving coal mine safety by identifying factors that influence the sudden release of gases in outburst prone zones Farhang Sereshki University of Wollongong Sereshki, Farhang, Improving coal mine safety by identifying factors that influence the sudden release of gases in outburst prone zones, PhD thesis, School of Civil, Mining and Environmental Engineering, University of Wollongong, 2005. This paper is posted at Research Online. IMPROVING COAL MINE SAFETY BY IDENTIFYING FACTORS THAT INFLUENCE THE SUDDEN RELEASE OF GASES IN OUTBURST PRONE ZONES. A thesis submitted in fulfilment of the requirements for the award of the degree DOCTOR OF PHILOSOPHY from UNIVERSITY OF WOLLONGONG by FARHANG SERESHKI B.Sc. (Hon.), M.Sc. Mining Engineering School of Civil, Mining and Environmental Engineering May 2005 IN THE NAME OF GOD This thesis is dedicated to my dear parents: My mother and father: Iran and Firooz My brother and sister: Farrokh, Frouzan and their families My dear uncle and his family and My dear daughter: Sarina For their love, encouragement, support and patience. AFFIRMATION I, Farhang Sereshki, declare that this thesis, submitted in fulfilment of the requirements for the award of Doctor of Philosophy, in the School of Civil, Mining and Environmental Engineering, Faculty of Engineering, University of Wollongong, is wholly my own work unless otherwise referenced or acknowledged. The thesis was completed under the supervision of A/Prof. N. I. Aziz and A/Prof. I. Porter and has not been submitted for qualification at any other academic institution. Farhang Sereshki May 2005 i The following publications are the result of this thesis project: Sereshki, F., Aziz, N. I., and Porter, I. (2003). Impact of Coal Permeability on Gas Sorption and Coal Volume Change. Proceedings of the 7th Annual Environmental Engineering Research Event Conference, The Cumberland, Marysville, Victoria, Australia, pp. 333-342. Sereshki, F., Aziz, N. I., and Porter, I. (2003). Improving Mine Safety by Identifying Factors that Influence the Sudden Release of Gases in Outburst Prone Zones. Proceedings of the 5th Congress on Safety, Occupational and Environmental health in Mines and related Industries, Kerman, Iran, pp. 33-44. (This conference paper was approved by the editorial committee as the best technical paper and won the best paper prize.) Sereshki, F., Aziz, N. I., and Porter, I. (2004). Influence of Gas Type and Pressure on Permeability and Volumetric Characteristics of Coal. Proceedings of the International Coalbed Methane Symposium, Univ of Alabama, Tuscaloosa, Alabama, USA, Paper No. 415. Aziz, N. I., Porter, I., and Sereshki, F. (2004). The Influence of Gas Environment on Coal Properties- Experimental Studies on Outburst Control. Proceedings of the 5th Underground Coal Operators’ Conference, Convened by the Illawarra Branch of The Australian Institute of Mining and Metallurgy, Univ. of Wollongong, NSW, Australia, pp.195-201. Sereshki, F., Aziz, N. I., and Porter, I. (2004). Cracking the Coal Matrix (Report on coal permeability tests using various gas pressures and axial loads). World Coal, Vol 13, No. 9, pp. 85-90. ii Sereshki, F., Bruggemann, D., Aziz, N. I., and Porter, I. (2005). Change in effective stress associated with coal shrinkage and gas sorption. Journal of the Mine Ventilation Society of South Africa, January/March, pp. 28-31. Sereshki, F., Aziz, N. I., Porter, I., and Godbole, A. (2005). Impact of Different Confining Gas Pressures on Coal Permeability and Modelling the Movement of Coalbed Gas. International Coalbed Methane Symposium, Uni. of Alabama, Tuscaloosa, Alabama, USA, pp. No. 502. Hutton, A., Bruggemann, D., Aziz, N. I. and Sereshki, F., (2005). Effect of Coal Properties on Gas Drainage. International Coalbed Methane Symposium, Uni. of Alabama, Tuscaloosa, Alabama, USA. Paper No. 501. Hutton, A., Bruggemann, D., Sereshki, F., and Aziz, N. I. (2005). Gas and Coal Properties Associated with Experimental studies in Outburst Control. The International Journal of Coal Geology (Refereed). Sereshki, F., Aziz, N. I. and Porter, I. (2005). Influences of coal type and rank on volumetric changes of coal and their impact on coal and gas outbursts. 20th World Mining Conference, Tehran, Iran (Abstract approved and manuscript submitted). Aziz, N. I., Sereshki, F., and Bruggemann, D. (2005). Status of Outburst Research at The University of Wollongong. 6th Underground Coal Operators’ Conference (Coal 2005). Convened by the Queensland Branch of The Australian Institute of Mining and Metallurgy, Brisbane, Queensland, Australia, pp. 283-289. Aziz, N. I., Sereshki, F., Bruggemann, D. and Porter, I. (2005). Parameters affecting mine gas drainage and outburst control research. 19th International Mining Congress and Fair. Izmir, Turkey (In press). iii ACKNOWLEDGMENTS The author would like to express his sincere gratitude to A/ Prof. N. I. Aziz for his supervision, encouragement, guidance and inspiration provided during the course of this research and providing the necessary facilities for this research. I would also like to express my sincere thanks to A/ Prof. I. Porter my thesis co-supervisor for his advice, encouragement and critical review of several aspects of this study. The author also wishes to express his sincere thanks for helpful contributions made by the following professionals during the period of this study: I wish to express my appreciation to A/ Prof. A. Hutton, Dr. T. Silver, Dr. A. Godbole, Mr. Saeid Hesami and Mrs Lorelle Pollard for their helpful comments and assistance. I also would like to thank the technical staff in the School of Civil, Mining and Environmental Engineering, especially Ian Laird and Alan Grant for their laboratory assistance and also Bob Rowlan, Ian Bridge, Nick MacKie and Greg Tillman. The author wishes to thank Mrs. Leonie McIntyre, Mr. Des Jemison and Mr. Peter Turner of the ITS staff for their contributions. The assistance provided by the Faculty of Engineering, University of Wollongong is also appreciated. I would also like to acknowledge with sincere appreciation, the financial support of the Ministry of Science, Research and Technology of the Islamic Republic of Iran and the University of Shahrood. Most importantly, I would like to express my deepest thanks to my parents and members of my family in Iran who have provided continued support throughout this study and indeed for my entire life. This study would not have been finished without support and encouragement from all my fellow Iranians at the University of Wollongong and their families. In particular, the author is indebted to Mr. Vahid Mottaghitalab, Mr. Mehrdad Bahrami Samani, Mr. Mohammad Mahdi Emamjomeh, Mr. Fardin Akhlaghiyan, Mr. Behzad Fatahi and Dr. Faramarz Doulati together with their respective families. iv ABSTRACT In recent decades, the subject of coal and gas outburst in underground coal mines has been a focus of interest in Australia and worldwide. Much of this interest has been the result of the alarming increase in outburst related incidents and associated fatalities world wide, particularly in China, Russia, Ukraine and other major coal producing countries. Australia, on the other hand, has seen a relative decline in outburst related incidents, for the last three years no outburst related incident has been reported. Effective gas drainage programmes, better management of outburst prone zones, tougher regulations and a continuing programme of dedicated vigilance and research have collectively contributed to improvements in outburst prevention. Still, however, difficult problems remain to be addressed. Geological disturbances such as dykes, shear planes and increased mineralisation can influence coal permeability and porosity. These disturbances must be fully understood in order to develop an effective on gas drainage programme and reduce outburst risks. Accordingly, a programme of laboratory studies was undertaken to investigate the relationship between coal composition, coal volumetric change and coal permeability. Coal samples for this study were obtained from four different coalmines in Australia (Tahmoor, Metropolitan, Dartbrook and North Goonyella) and Tabas coalmine in Iran. Coal samples were tested in different types of gases and under different gas pressures and stress conditions. Coal permeability tests were conducted in the gas pressure chamber of the multi-function outburst research rig (MFORR), and the volumetric v change tests were carried out in a modified pressure bomb. Microscopic studies provided a better correlation between coal composition permeability and shrinkage characteristics. A numerical model was developed to simulate single gas flow through a coal sample. The simulation further supported the experimental studies. The petrographical tests showed that most of the Australian coals tested were inertinite rich coals. The mineral matter in the Australian coal samples were mostly carbonate (calcite) and clay, but the Iranian Tabas coal had pyrite as the dominant mineral matter. Tabas coal has the highest vitrinite concentration (70%) and lowest proportion of inertinite elements (8.18%), the lowest vitrinite content was obtained from North Goonyella coal. There was a definite correlation between coal composition, coal volumetric change and coal permeability. Volumetric strain changes during the adsorption stage in all gas environments were greater than the volumetric strains in the desorption stage. The level of coal shrinkage was affected by the type of gas desorbed. Carbon dioxide appears to have the greatest influence on the matrix and nitrogen the least. The permeability of coal was also influenced by the gas type and pressure. Greater gas permeability was obtained in N2 gas, and the lowest permeability was obtained in a CO2 environment. The sorption characteristics of CO2 are a major factor. The degree of coal permeability is reduced exponentially by increasing the applied stress and also by increasing the confining gas pressure, irrespective of the gas type. The permeability tests showed that with an increased inertinite content the permeability of vi coal increased, except in the case of Tahmoor Colliery 900 Panel which showed a decrease. Comparison of the Tahmoor coals from 800 and 900 Panels showed that the permeability of coal was influenced by the mineral content and the carbonates, as well as the cavities. In particular; there was a reduction in coal permeability with increasing mineral content and carbonate content of the coal. With an increase in the percentage of inertinite, the permeability of coal increased. The numerical modelling provided an opportunity to quantify the flow mechanism in coal. It was possible to simulate the flow duration across the coal samples as a function of time with different gases and coal types. It was recommended that the study be extended to include more coal deposits and coals with different geological variations, so that an effective data bank can be established for Australian coals. vii TABLE OF CONTENTS TITLE PAGE AFFIRMATION ................................................................................................................ i ACKNOWLEDGMENTS ............................................................................................... iv ABSTRACT........................................................................................................................v LIST OF FIGURES ....................................................................................................... xii LIST OF TABLES ........................................................................................................ xix LIST OF SYMBOLS AND ABBREVIATIONS ..........................................................xx CHAPTER 1. GENERAL INTRODUCTION.................................................................................. xii 1.1 INTRODUCTION .................................................................................................... 1 1.2 COAL AND GAS OUTBURST............................................................................... 3 1.3 STATEMENT OF THE PROBLEM ........................................................................ 4 1.4 OBJECTIVES OF RESEARCH ............................................................................... 5 1.5 RESEARCH PROGRAMME................................................................................... 6 1.6 THESIS OUTLINE................................................................................................... 7 2. OUTBURSTS – A REVIEW OF MECHANISMS OF GAS FLOW IN COAL ....11 2.1 INTRODUCTION .................................................................................................. 11 2.2 COALIFICATION PROCESS ............................................................................... 11 2.2.1 Stages of the coalification process................................................................... 12 2.2.2 Gases in Coal ................................................................................................... 14 2.2.3 Effect of igneous intrusions ............................................................................. 17 2.3 PHYSICAL STRUCTURE OF COAL................................................................... 19 2.4 GAS SORPTION IN COAL................................................................................... 22 2.5 TRANSPORT OF GAS IN COAL ......................................................................... 29 2.6 STRENGTH OF COAL.......................................................................................... 36 2.7 SUMMARY............................................................................................................ 38 viii 3. A REVIEW OF THE IMPACT OF COAL PROPERTIES ON GAS SORPTION …………………………………………………………………………………………39 3.1 INTRODUCTION .................................................................................................. 39 3.2 COAL MATRIX CHANGE ................................................................................... 39 3.2.1 Early research on coal matrix shrinkage related to sorption............................ 40 3.2.2 Modelling matrix shrinkage effects on coalbed methane recovery ................. 59 3.3 COAL PERMEABILITY ....................................................................................... 63 3.4 FACTORS AFFECTING THE PERMEABILITY OF COAL .............................. 66 3.4.1 Effective stress ................................................................................................. 66 3.4.2 Coal Petrography ............................................................................................. 70 3.4.3 Mineralisation .................................................................................................. 72 3.4.4 Degree of fracturing......................................................................................... 77 3.4.5 Gas pressure and type ...................................................................................... 79 3.4.6 Water................................................................................................................ 82 3.5 PERMEABILITY CLASSIFICATION OF COAL-BEDS .................................... 84 3.5.1 Drainage classification..................................................................................... 84 3.5.2 Outburst classification ..................................................................................... 87 3.6 SUMMARY AND CONCLUDING REMARKS .................................................. 89 4. COAL PETROGRAPHY............................................................................................91 4.1 INTRODUCTION .................................................................................................. 91 4.2 SAMPLE COLLECTION....................................................................................... 91 4.3 SAMPLE PREPARATION .................................................................................... 93 4.3.1 Microscopy ...................................................................................................... 95 4.4 PETROGRAPHICAL TEST RESULTS ................................................................ 98 4.4.1 Tabas coal samples .......................................................................................... 98 4.4.2 Tahmoor coal samples ................................................................................... 100 4.4.3 Dartbrook coal samples.................................................................................. 103 4.4.4 Metropolitan coal samples ............................................................................. 105 4.4.5 North Goonyella coal samples ....................................................................... 107 4.5 DISCUSSION AND SUMMARY........................................................................ 108 ix 5. INFLUENCES OF GAS ENVIRONMENT ON VOLUMETRIC COAL MATRIX CHANGE .....................................................................................................................111 5.1 INTRODUCTION ................................................................................................ 111 5.2 COAL SAMPLE PREPARATION ...................................................................... 112 5.2.1 Sample Instrumentation ................................................................................. 113 5.2.2 Sample preconditioning and testing............................................................... 114 5.3 VOLUMETRIC CHANGE DUE TO ADSORPTION – RESULTS ................... 118 AND DISCUSSION ................................................................................................... 118 5.4 COAL SHRINKAGE BY DESORPTION ........................................................... 126 5.5 CONCLUSIONS................................................................................................... 133 6. THE EFFECT OF GAS PRESSURE AND AXIAL STRESS ON COAL PERMEABILITY ..........………………………………..……………………….....134 6.1 INTRODUCTION ................................................................................................ 134 6.2 EXPERIMENTAL PROCEDURE ....................................................................... 135 6.3 TEST RESULTS................................................................................................... 139 6.3.1 The effect of applied load................................................................................ 142 6.3.2 The effect of coal composition ...................................................................... 147 6.3.3 The effect of gas Types.................................................................................. 147 6.3.4 Effect of loading stress................................................................................... 157 6.4 MODELLING THE FLOW OF GAS FROM COAL CORES ............................ 160 6.4.1 Modelling procedure...................................................................................... 160 Basic parameters of the model .................................................................................... 167 6.5 CONCLUSIONS................................................................................................... 175 7. CASE STUDY AND OVERALL DISCUSSION OF RESULTS...........................176 7.1 INTRODUCTION ................................................................................................ 176 7.2 SITE INVESTIGATION ...................................................................................... 176 7.3 COAL PETROGRAPHY TESTS......................................................................... 179 7.4 SHRINKAGE TESTS..............................................................
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  • Fall '07
  • ........., Coal, Coal Properties- Experimental Studies, International Journal of Coal Geology

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