Coalbed methane: From hazard to resource

International Journal of Coal Geology 35 Ž1998. 3–26

Coalbed methane: From hazard to resource Romeo M. Flores

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US Geological SurÕey, DenÕer, CO 80225, USA Received 14 April 1997; accepted 1 May 1997

Abstract Coalbed gas, which mainly consists of methane, has remained a major hazard affecting safety and productivity in underground coal mines for more than 100 years. Coalbed gas emissions have resulted in outbursts and explosions where ignited by open lights, smoking or improper use of black blasting powder, and machinery operations. Investigations of coal gas outbursts and explosions during the past century were aimed at predicting and preventing this mine hazard. During this time, gas emissions were diluted with ventilation by airways Že.g., tunnels, vertical and horizontal drillholes, shafts. and by drainage boreholes. The 1970’s ‘energy crisis’ led to studies of the feasibility of producing the gas for commercial use. Subsequent research on the origin, accumulation, distribution, availability, and recoverability has been pursued vigorously during the past two decades. Since the 1970’s research investigations on the causes and effects of coal mine outbursts and gas emissions have led to major advances towards the recovery and development of coalbed methane for commercial use. Thus, coalbed methane as a mining hazard was harnessed as a conventional gas resource. q 1998 Elsevier Science B.V. Keywords: coal gas outburst; coalbed methane; hazard; resource assessment; recoverability

1. Introduction Coalbed gas has been considered a major mine hazard since the early to mid 19th century when the first documented coal mine gas explosions occurred in the United States in 1810 and in France in 1845. Since the late 20th century coalbed methane has received increased emphasis as a potential energy resource. Coal beds contain a mixture

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of gases in which methane makes up 80–99% and varies from 0.0003–18.66 m3rmetric ton Ž0.01 to ) 600 ft 3rton. with heat combustion ranging from 8455 to 9345 calrm3 Ž950–1050 Bturft 3 . ŽKemp and Petersen, 1988.. Minor amounts of carbon dioxide, nitrogen, hydrogen sulphide, and sulphur dioxide make up the other components of coalbed gas. A minimum amount of gas is contained as ‘free gas’ in fractures Žcleat system., but it mainly occurs as sorbed gas on micropore surfaces in the matrix of coal beds. In addition, some of the coalbed gas migrates from the coal into adjacent sandstones. Early research investigations of coalbed gas have concentrated on technology to control and manage gas outbursts and explosions ŽLama, 1995.. Methane research in the United States was separate from health and safety research ŽDeul and Kim, 1986.. Since the 1970’s when coalbed methane was determined to be an economically viable energy source, investigations have focused on understanding its origin, occurrence, distribution, availability, producibility, and recoverability. Investigations of coalbed gas in the United States underground bituminous coal mines in the mid 1970’s showed a production of 7 = 10 9 m3rd Ž) 200 million cubic feet per day or mmcfgpd. of methane per day ŽSkow et al., 1980.. Degasification of underground coal mines by draining methane either by horizontal boreholes at the base of mine shafts or by outside mine entries and vertical boreholes in advance of mining have led to concerns about the contribution of methane to the ‘greenhouse effect’ of the atmosphere. During the course of investigations concerning the gas emissions into the atmosphere, it has become apparent that methane from underground coal mines is a viable energy source. In the United States this effort was enhanced by pioneering work of government agencies Že.g. US Bureau of Mines or USBM, US Department of Energy or DOE, and Gas Research Institute or GRI. developing the technology to recover coalbed methane. However, it was not until the vertical wells unrelated to mining operations, were drilled in the central Appalachian, Black Warrior, and San Juan Basins in mid 1970’s that coalbed methane was pronounced a viable commercial energy commodity. The most important factor that has influenced the producibility of coalbed methane in the United States is enactment of the ‘Crude Oil Windfall Profit Tax of 1980’ ŽSoot, 1988.. This tax-credit incentive was proposed for production of unconventional fuels from: Ž1. oil shale and tar sands, Ž2. gas from biomass, geopressured brines, or Devonian shale, Ž3. liquid, gaseous or solid synthetic fuels from coal, Ž4. some processed wood fuels, and Ž5. steam from some agricultural by-products. This production tax credit permitted coalbed methane producers to receive $0.75 per million Btu of gas sold in 1986, which rose to $0.78 per million Btu in 1987. This tax credit was projected to increase $1.34 per million Btu in 2001. However, in order to qualify for the tax credit, wells must have been drilled by 1990; production from these wells is eligible for credit until 2001. Thus, the current focus on coalbed methane is on providing safe mining operations, utilization of methane as a unconventional energy source Žand resulting tax writeoff., and its effect on the environment. In the past this progression of interests provided a vehicle for research investigations that led to coalbed methane becoming a significant part of the energy resource and a target for exploration and development worldwide. This paper summarizes the historical and geological perspectives of the state of knowledge and research advances in coalbed methane as a conventional energy resource.

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2. Historical perspective in coal mining Historically, coalbed methane was vented to conduct safe mining operations in order to increase mine productivity. Coalbed methane was not a problem when coal was mined from outcrops by stripping and shallow shafting in the United Kingdom and other European countries. As shallow coal resources were slowly exhausted at the end of the 18th century and technology was improved to permit construction of large deep mines, coalbed methane in these mines was observed. In the early 19th century, coal mine explosions were recorded in Britain, France, and United States. In the late 19th and early 20th century minor to major disastrous explosions were reported in deep underground coal mines in Australia, Canada, Belgium, Germany, Japan, Poland, Russia, and United States. In all these cases, poor gas ventilation or no gas drainage ŽDiamond, 1994. allowed coalbed methane to accumulate in amounts which could be ignited either by open lights, smoking or improper use of black blasting powder, and sparking from mining equipment. In addition, coal dust propagated explosions through large sections of the mines. Outbursts were described by Hargraves Ž1983. as violent projections of coal, gas, and rocks from the floor and roof away from the freshly exposed coal face during mining operations. These phenomena may result in explosion if an ignition source is present; however, they do not always result in an explosion. Campoli et al. Ž1985. indicate that outbursts are caused by high coalbed gas pressure and structural stress created by the load on the mine and are generally not common in the United States. Outbursts are not only restricted to underground coal mines but also occur in salt, potash, and other mines ŽGimm and Pforr, 1964; Mahtab, 1982; Styles, 1995.. However,

Fig. 1. A diagram showing the relationship of annual fatalities from coal-mine explosions and the influence of mine safety research. During the period of 1900–1940, the first application of rock dusting, permissible use of electrical equipment, and improved ventilation were enforced. During the period from 1940–1980 the coal mine health safety, rock dust-coal analyzer, methane degasification, and explosion-proof bulkheads were enforced Žmodified from Deul and Kim, 1986..

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these violent failures are more prevalent and pronounced in underground coal mines because of the development of high pressures and large quantities of methane, carbon dioxide or both stored in the coal. For instance in 1981, the largest ever underground coal-mine outburst in Japan expelled 4000 m3 Ž140,000 ft 3 . of coal and up to 600,000 m3 Ž21 mmcf. of gas ŽDeguchi et al., 1995.. Lama and Bodziony Žthis Special Issue. indicate that an equally large outburst previously occurred in 1969 in the Gagarin coal mine in the Donetsk Basin in Ukraine, which ejected 14,000 tons of coal and 600,000 m3 of gas. Although coal mining in the United States began in the early 18th century, mine explosions in the Appalachian coal basin occurred intermittently in the early to middle 19th century, becoming more frequent from the late 19th century to the middle of the 20th century as described by Deul and Kim Ž1986.. These workers indicate that the annual number of fatalities from explosions in underground coal mines in the United States has diminished through the last 80 years because of research on mine safety Žsee Fig. 1.. In contrast, more than 15,000 coal-gas outbursts or explosions have occurred in China during the same time ŽDeguchi et al., 1995. with a resulting large number of fatalities and injuries Že.g., ) 10,000 to date in China, in Murray, 1996; Humphrey, 1960; Machisak et al., 1961; Moyer and Jones, 1968; Skow et al., 1980; Litwiniszyn, 1995.. Worldwide, most of these underground coal-mine gas outbursts or explosions were caused by coalbed methane ŽAnderson, 1995; Lama, 1995; Okten et al., 1995..

Fig. 2. Relationship of gas pressure and content gradients to outbursting and non-bursting conditions in the Gemini coal seam, Leichhardt Colliery, Bowen Basin, Australia Žmodified from Hanes, 1995..

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Outbursts involving the carbon dioxide component of the coalbed gas are more violent than those related to methane because the sorptive capacity of coal for carbon dioxide is 2–3 times greater than that for methane and the desorption rate of carbon dioxide is much faster than methane, yielding a high pressure gradient ŽStyles, 1995.. However, coalbed methane is a major factor in outbursting or explosions worldwide and a coalbed with methane content greater than 9 m3rmt is considered coal and gas outburst prone ŽCampoli et al., 1985.. In addition a high gas pressure gradient also contributes to outbursting as shown in Fig. 2 ŽHanes, 1995.. Research on coalbed methane for the past several decades has been directed toward its management, control, and prediction in order to reduce outbursts in underground coal mines ŽDeul, 1964; Kozlowski, 1980; Janas, 1985; Tarnowski, 1988; Noack, 1995; Sergeev and Ivanov, 1995; Hatherly et al., 1995; Murray, 1996.. Because coalbed gas outbursts occur in mines worldwide, a unified effort toward solving this problem started before World War I ŽLoiret and Laligant, 1923.. This effort has resulted in intensive research investigations on the causes of underground coal-mine gas outbursts outside the United States where outbursts are more common. These investigations were designed to help predict, prevent, and manage coal-mine gas outbursts and include the origin and mechanism of coal-mine outbursts. 2.1. Origin and mechanism of coal-mine outbursts It was suggested by Kotarba Ž1990. that rock aggregates in the earth’s crust by virtue of their physical and chemical characteristics consist of a network of structures that include fractures, micro-cracks and pores, which were filled with gaseous and liquid substances. Coal is one such rock aggregate that accumulated gaseous substances such as carbon dioxide, methane, andror nitrogen in these structures during coalification. Coal consists of organic and inorganic matters, which have undergone a series of devolatilization stages during coalification into higher grades or ranks Že.g. lignite, subbituminous, bituminous, and anthracite.. Low rank coals Že.g. lignite and subbituminous. lose a minor amount of volatile matter during the process of coalification. High rank coals Žbituminous and anthracite. lose a large amount of volatile matter during this process, producing methane, carbon dioxide, nitrogen, and large amounts of water. Coalbed methane generated at low temperature is of a biological Žbiogenic. origin and that generated at high temperature is of a thermal origin Žthermogenic. ŽMeissner, 1984; Rightmire, 1984; Rice, 1993.. There is a continuing debate on the mechanism responsible for outbursts in underground coal mines. Cheng and Ding Ž1971. suggested that the driving force of coal-mine outbursts is the internal energy of the gas contained in the coal bed rather than the stressrstrain energy of the coal bed and surrounding rocks. Gas pressure and gas quantity are significant factors in coal-mine outbursts ŽKhodot, 1961; Christianovich, 1953; Christianovich and Salganik, 1983; Lama, 1995.. In addition, rock pressure and strength are also important factors contributing to coal-mine outbursts as suggested by Christianovich and Salganik Ž1983.. These researchers argue that a continuous medium Že.g. coal bed. is divided into several zones Že.g. elastic, oriented cracks, plastic. due to

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existing strain. Mining activity is interpreted to displace these zones; gas is released and migrates into the plastic zone, which serves as a sponge and a barrier. The thinner this barrier, the greater the probability of a outburst. Mroz and Zacharski Ž1990. supported this argument by indicating the existence of oriented cracks Žor ‘slices’.. ‘Thin slices’ provide conduits of gas flow between them. Rock ‘slicing’ is confirmed in laboratory experiments by Bodziony et al. Ž1990. and Gawor et al. Ž1991.. This mechanism of propagating coal-mine outbursts led to a concentrated effort to understand the topology of continuous to multi-phase medium ŽRyncarz, 1989, 1990; Majewska, 1990; Litwiniszyn, 1987, 1995; Gotoh et al., 1995; Bodziony and Kraj, 1995; Chen et al., 1995; Tarnowski, 1995; Topolnicki, 1995.. Other mechanisms of coal-mine outbursts are directly related to microseismic activity propagated by reactivation of faults and explosives ŽDavies et al., 1987; Styles, 1995. as well as indirectly associated with the maceral composition of the coal ŽBeamish and Crosdale, 1995.. 2.2. Prediction and preÕention of coal-mine outbursts Knowledge gained through investigations of the origin of coalbed gas and mechanism of coal mine outbursts has enhanced the techniques of prediction and prevention of outbursts and explosions. Prediction includes monitoring of gas emissions ŽLama, 1995., of acoustic signal spectrum characteristics in relation to structures in the rock mass Že.g. state of stress; Bobrov, 1995; Deguchi et al., 1995; Hatherly et al., 1995; Seto and Katsuyama, 1995; Birukov, 1995., and of microseismic acoustic emissions ŽStyles, 1995; Talebi et al., 1995.. The techniques of prediction may be applied to control and prevent underground coal-mine outbursts. For example measurements of gas content and pressure from drillholes on the surface and subsurface permits determination of threshold conditions for outburst occurrence ŽZhang, 1995.. These measurements provide information on the irregular distribution of gas and change in gas trends allowing the emplacement of methods to control and prevent coal-mine outbursts. In addition, mining methods and machinery may be modified and designed Že.g. influence on coal room and pillars, longwall panel, etc.. to account for rock-mass stresses, which could trigger coalbed gas outbursts from an advancing mine face. Different methods of gas ventilation or drainage also may be adopted such as removal of gas by vertical wells in advance of mining or vertical gob wells drilled into the cave area behind the longwall panel. Thus, information on prediction, control, and prevention of gas emission and associated outbursts is important not only in planning the ventilation of mines but also in planning mine workings, development, and production Že.g., determining the length of the coal face., which in turn, influence the total coal production ŽZabourdyaev, 1995.. This, in turn, directly relates to mine safety, efficiency of mine operations, and mine economics.

3. Geological perspectives in coalbed methane development Gas dilution by ventilation during active mining operations and post- and pre-mining methane drainage activity mainly has been conducted in order to improve mine safety,

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increase productivity, and improve mining economics. However, ventilation and drainage efforts related to underground mining has also led to production of coalbed methane by conventionally drilled vertical wells ŽDiamond et al., 1989; Diamond, 1994; Dunn, 1995.. Production was followed by successful recovery and sale of coalbed methane into the conventional natural gas markets ŽDunn, 1984.. This economic utilization of coalbed methane not only stimulated significant commercial interest but also focused interest and research on the geological factors that are directly related to their accumulation, distribution, and recoverability ŽGamson and Beamish, 1992.. 3.1. Towards exploration of coalbed methane Because coalbed methane exploration has gone beyond coal mining areas into undeveloped coal-bearing basins, strategies of exploration require an understanding of the factors leading to concentrations or accumulations of methane. Coal rank may be the most traditional factor in locating concentrations of methane. Although an oversimplification, it is believed that the type of coalbed gas Žmethane vs. carbon dioxide. generated during the entire process of coalification varies with rank ŽFig. 3; Hunt, 1979.. In general, during early stages of coalification Že.g., formation of lignite to subbituminous rank coals. a large amount of carbon dioxide is generated. During the later stages of coalification Že.g., formation of high volatile bituminous to anthracite rank coals. a large amount of methane is generated Žabout 100–300 cm3rgm of coal.. However, the methane yield is also influenced by the coal maceral content ŽFig. 4; Juntgen and Karweil, 1966; Higgs, 1986; Levine, 1987.. Another factor to consider in the accumula-

Fig. 3. Diagram showing the amount of gas generated from coal during coalification. Žmodified from Hunt, 1979..

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Fig. 4. Cumulative methane generation curves for a perhydrous German Tertiary coal and a subhydrous Carboniferous coal of the United States. Total gas generation Žshaded. is about equal between the two coals Žmodified from Higgs, 1986..

tion of methane is that coal may generate more methane than it can store; thus coalbed gas may be expelled and migrate to adjacent reservoirs, such as sandstone beds, during coalification into higher ranks ŽRice, 1993.. In addition, methane storage capacity of coal increases with increasing pressure and decreases with increasing temperature ŽMeissner, 1984.. Levine Ž1991. argues that the storage capacity of coal is affected by its maceral composition, as well. The amount of inorganic matter also affects storage capacity in a very significant way. Successful exploration for methane accumulations also requires understanding of areas where rock-mass permeability may have been altered ŽClark and Boyd, 1995.. Increased permeability in rock masses occur in areas affected by shear or torsional loads which may in turn be affected by local structural Že.g. folding, faulting. and regional deformation Že.g. compressional.. Stress modeling utilizing these mechanisms stimulates changes in rock volume, which are accompanied by modification in gas permeability and storage capacity. Permeability is also controlled by the fracture types and orientations of the coal bed. The fracture systems Že.g. face and butt cleats. in coal beds and their geometry Že.g., orthogonal vs. perpendicular to bedding surfaces. are best described by Close Ž1993.. Although natural coal fracture systems result from coalification, stress

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due to tectonic or structural deformation and compaction by sediment loading ŽAmmosov and Eremin, 1960; Ting, 1977; Law et al., 1991. may also cause their development. The density of the fracture systems, and therefore increased storage capacity for gas, has been directly associated with coal composition, thickness, and rank ŽLaw et al., 1991; Levine, 1992; Law and Rice, 1993.. Thus, recognition of permeability of coal reservoirs is essential in understanding the accumulation of methane and its drainage; however, a knowledge of associated exogenic fractures Žtectonic. is equally important ŽDecker et al., 1992; Koenig et al., 1992.. 3.2. Distribution of coalbed methane and resource assessment A simplified method of investigating the distribution of coalbed methane is associated with assessing coal resources in coal-bearing basins or coalfields ŽHobbs, 1978; Rightmire, 1984; Tyler et al., 1997.. Because coal resource assessment is directly related to finding potential minable beds in the shallow parts Ž- 915 m or - 3000 ft. of coal basins or coalfields, investigation of high-potential areas for coalbed methane resources may be extended into the deeper parts of these areas. In the conterminous United States, ICF Resources Ž1990. analyzed in-place methane resources in major coal-bearing coal basinsrcoalfields in the United States ŽFig. 5. in which the coal beds range from Pennsylvanian to Tertiary in age and from bituminous to subbituminous in rank. On the basis of this study, in-place methane resources in these coal basins and coalfields were estimated to be between to be 11.3 Bm3 Ž400 Tcf. of which 2.5 Bm3 Ž90 Tcf. are potentially recoverable. However, the latest estimate by Tyler et al. Ž1997. of in-place gas in the United States is about 19 Tm3 Žalso see Bibler et al., this Special Issue.. This in-place methane resource estimate is smaller than that of Alaska in which coal resources Ž5.3 trillion metric tons or 5.8 trillion short tons. exceed 40% of the total resources in the conterminous United States ŽMerritt and Hawley, 1986; Stricker, 1991.. Smith Ž1995. estimated that these coals contain more than 28 Tm3 Ž1000 Tcf. of methane. In Alaska the coals are equally as high rank and as old ŽMississippian to Tertiary in age. as those in the conterminous United States ŽStricker, 1991.. A majority of these coals are contained in Cretaceous and Tertiary rocks. An estimate of the Cretaceous and Tertiary coal resources Žsubbituminous B to high-volatile bituminous in rank. by Stricker Ž1991, 1993. is 4.5 trillion metric tons Ž5 trillion tons.. Based on this estimate and additional information from Smith Ž1995., Stricker Ž1993. and Flores et al. Ž1997., it is estimated that the in-place coalbed methane resource of 7 Cretaceous and Tertiary coal-bearing basinsrcoalfields in Alaska ŽFig. 6. is as much 22 Tm3 Ž786 Tcf.. Thus, about 80% of the total methane resource of Alaska is contained in the Cretaceous and Tertiary coal basinsrcoalfields and majority of this resource lies beneath the offshore and onshore North Slope and Cook Inlet Basins ŽFig. 6.. Site-specific evaluation of the distribution of coalbed methane in the coal basins in the western conterminous United States is summarized by Tyler et al. Ž1992.. This investigation emphasizes the importance of regional deformation in predicting the distribution of methane in association with fracture permeability. Thermal maturation maps based on vitrinite–reflectance studies were made by Amuedo and Bryson Ž1977.,

12 R.M. Floresr International Journal of Coal Geology 35 (1998) 3–26 Fig. 5. A map showing coal basinsrcoalfields in the United States and estimates of in-place coalbed methane resource. Modified from ICF Resources Ž1990., Tyler et al. Ž1997. and Bibler et al., 1998 this volume..

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Fig. 6. A map of 7 Cretaceous and Tertiary coal basinsrcoalfields in Alaska and estimates of the in-place coalbed methane resource ŽStricker, 1993; Smith, 1995; Flores et al., 1997.. Gray shades in the North Slope and Cook Inlet Basins are offshore areas.

Freeman Ž1979., Law Ž1992., Waller Ž1992., and Nuccio and Finn Ž1994. in order to maximize efforts in exploring for high potential methane areas in the coal basins or coalfields in the United States. In general, these studies indicate that the thermal maturity of basins is due to burial history, circulation of hot fluids, and high heat flow from a deep seated source ŽFig. 7.. Based on vitrinite reflectance Ž R o . the deeper part of the coal basins has achieved R o ) 0.6% allowing thermogenic gas generation ŽRice, 1992; Law, 1992; Nuccio and Finn, 1994.. Where R o values are - 0.6% the coal-bearing basin is thermally immature for significant thermogenic gas generation but does not preclude biogenic gas generation ŽRice, 1992.. Based on these studies, most of the coal basins in the United States have reached a sufficiently high thermal maturity to exceed the threshold of significant methane generation ŽRightmire et al., 1984; Tyler et al., 1992; Waller, 1992.. However, a large amount of biogenic gas accumulations occur in six Tertiary coal-bearing basins in the northern Rocky Mountains region ŽFig. 8.. The vitrinite reflectance trends in these basins show decreasing R o values Žor greater potential for biogenic gas accumulations. toward the northeastern part of the Rocky Mountains region ŽNuccio and Finn, 1994; Pontolillo and Stanton, 1994.. The decreasing vitrinite reflectance values to the north and east shown in Fig. 8 are related to the migration and younging of Paleocene Laramide deformation fronts ŽFlores et al., 1994; Perry and Flores, 1997.. That is, coals formed in basins associated with early deformation fronts Žsee Fig. 8; Laramide uplifts 1 and 2. resulted in deep burial and rapid basin subsidence; thus, high thermal conditions. Coals formed in basins related to later deformations fronts Žsee Fig. 8; Laramide uplift 3. are affected by shallow burial and less rapid basin subsidence; hence, low thermal conditions. The Paleocene coals in these

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Fig. 8. Map showing variations of vitrinite–reflectance values in six Tertiary coal basins in the northern Rocky Mountains region of the United States. Vitrinite–reflectance values in each basin decrease towards the north and east as influenced by younging of Laramide deformation fronts Že.g., Laramide uplifts: Ž1. early Paleocene, Ž2. middle Paleocene, and Ž3. late Paleocene.. Modified from Pontolillo and Stanton Ž1994., Nuccio and Finn Ž1994., Flores et al., 1994, and Perry and Flores Ž1997..

six basins probably contain greater than 0.9 Tm3 Ž32 Tcf. of methane resources that are mainly biogenic in origin ŽRice, 1993.. The approach in the United States to investigating the accumulation and distribution of coalbed methane in coal-bearing basins or coalfields containing abundant coal resources is also used in Australia, New Zealand, China, and Europe ŽGray, 1991; Mallett and Russell, 1992; Vance and Cave, 1992; Murray, 1996; Gayer and Harris, 1996.. In eastern Australia, interconnected Permian and Triassic coal basins have been explored for coalbed gas. There vitrinite reflectance, which ranges from 0.6% to 3.0% ŽFig. 9., displays a level of thermal maturity in which thermogenic gas may have been generated in the eastern parts of the basins ŽMallett and Russell, 1992.. The western margins of the basins exhibit - 0.6% vitrinite reflectance, suggesting a possible biogenic methane source. The thermal maturity in the eastern part of the basins is probably controlled by either high heat flow or deep burial. Other Permian and Carboniferous basins in eastern Australia display vitrinite reflectance values ranging from 0.35%–0.7%, which would allow generation of mainly biogenic methane with subordinate thermogenic methane ŽDurie et al., 1992.. A study of the isotopic composition of bituminous coals in eastern Australia ŽSmith and Pallaser, 1996. indicates that

Fig. 7. A map of a typical thermally mature coal basin ŽRaton Basin. in Colorado and New Mexico in the United States. The basin contains Cretaceous and Tertiary coals affected mainly by high heat flow ŽHFU. due to igneous intrusions. Modified from Amuedo and Bryson Ž1977. and Dolly and Meissner Ž1977..

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Fig. 9. A map showing thermal maturity, as indicated by vitrinite–reflectance values of the Late Permian coals in the Bowen–Gunnedah–Sydney Basins, Australia Žmodified from Mallett and Russell, 1992..

microbial reduction of carbon dioxide played a major role and thermal decomposition a minor role in methane generation. In New Zealand the distribution of coalbed methane has also been associated with coal basins and coalfields containing abundant coal resources ŽVance and Cave, 1992.. These workers indicate that New Zealand coalfields contain 15.7 Btu of in-place coal resources of which 65% are lignite and 35% are subbituminous and bituminous ranks Žvery minor semi-anthracite and anthracite.. Although lignite comprises a large part of the in-place coal resources, this low-rank coal resource is mainly found in a few coalfields ŽFig. 10; Sherwood, 1986.. Most of the high-volatile bituminous coals are found in coalfields in the northern part of South Island. Regional syntheses of thermal maturity of these high rank coals in South Island based on vitrinite reflectance indicates R o values varying mainly from 0.45% to 1.2%, with extreme values from 0.3% to 1.7% ŽSuggate, 1959; Nathan et al., 1986.. Four major coalfields exhibit R o ) 0.75%, which

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Fig. 10. A diagram showing the range of coal ranks within New Zealand coalfields of Cretaceous and Tertiary age Žadopted from Sherwood, 1986..

may indicate thermogenic gas generation ŽFig. 11.. The thermal maturity of these coal basins and coalfields is controlled by heat flow from shallow to deep seated igneous intrusions ŽNathan et al., 1986.. Investigations of the distribution of coalbed methane in China are concentrated in the northern and eastern coal basins ŽDai et al., 1987; Rice, 1993; Murray, 1996.. In northern China, Permian and Carboniferous anthracite resources have been determined to be a viable source of coalbed methane ŽMurray, 1996.. Coals in this part of China range from semi-anthracite to anthracite with R o values ranging from 2.4% to 6.0%. These coals are well fractured by tectonic deformation, which makes them good gas reservoirs. The eastern China coals vary from Carboniferous to Tertiary in age and from high volatile bituminous to anthracite with R o values from 0.5 to 3.8% ŽRice, 1993.. The study of Dai et al. Ž1987. indicates a direct correlation between rank and depth. Coals with R o values from 1.0% to 1.7%, or high volatile A to medium volatile bituminous, contain wet gas. However, coals at shallow depths with wide ranging R o values are methane-rich. Zhang and Chen Ž1985. identified the presence of biogenic methane in some northeastern China coalfields. The Carboniferous coal-bearing rocks in England, Germany, and Poland have been the objectives of coalbed methane exploration ŽGayer and Harris, 1996.. Variscan foredeep coal basins in England have been determined by Fails Ž1996. to have potential coalbed methane accumulations. In western Germany, hardcoal resource, which is 454 = 10 9 m3 of coal, may translate to 1 = 910 3rm3 of in-place gas ŽJuch, 1996.. The Carboniferous coals of the Ruhr District may yield as much as 151 = 10 9 m3 of in-place

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Fig. 11. Map showing variations of vitrinite-reflectance values of coals in Cretaceous and Tertiary coal-bearing basins and coalfields in northern South Island, New Zealand Žadopted from Nathan et al., 1986..

gas ŽFreudenberg et al., 1996.. Colombo et al. Ž1970. studied the carbon isotopic composition of coalbed gases in the coal district in western Germany, and found that methane becomes isotopically heavier at depth. These coals vary from high-volatile A bituminous to anthracite Ž R o values of 0.8–4.9%.. In Poland, Carboniferous coals, which vary in rank from high-volatile A bituminous to anthracite Ž R o values between 1.1–2.6%., are considered potential sources of thermogenic methane gas accumulations ŽKotarba, 1988..

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3.3. RecoÕerability of coalbed methane and production Reservoir characterization of coal beds and its relation to recoverability and producibility of methane has been the focus of research since the late 1960’s. Ever since the first successful production from test wells in the Black Warrior Basin in the United States, research investigations into more efficient methods of recovering coalbed methane have continued. Recoverability and volume Žin-place gas. of methane accumulations depend on the rank, composition, quality, permeability, and porosity of the coal reservoirs; pressure–temperature conditions; and well completion and stimulation techniques ŽEttinger et al., 1966; Faiz et al., 1992; Gamson and Beamish, 1992; Harpalani and Chen, 1992; Paterson et al., 1992; Beamish and Crosdale, 1995.. Faiz et al. Ž1992. indicated that the amount of gas retained in coal beds is controlled by rank, maceral and mineral composition, porosity, pressure, temperature, and related structural–tectonic conditions. Ettinger et al. Ž1966. suggested that low- to medium-rank coals and inertinite-rich coals have a higher capacity for methane sorption than vitrinite-rich coals. However, in higher rank coals with both maceral types, methane sorption is similar in amounts. The methane sorption capacity of vitrinite is greater than inertinite as shown by Beamish and Crosdale Ž1995. in their investigation of the coals in the Bowen Basin in eastern Australia. Their study indicates that the inertinite-rich coals have greater porosity than vitrinite-rich coals. For high- to low-volatile bituminous coals, inertinite-rich coals are characterized by macropores and vitrinite-rich coals by micropores. However, Beamish and Crosdale Ž1995. concluded that vitrinite-rich coals appear to have a higher sorption capacity than inertinite-rich coals but vitrinite-rich coals have a slower desorption rate than inertinite-rich coals. Methane recoverability and production from coal beds and their relationships to coal type, microstructure, and gas flow were studied by Gamson and Beamish Ž1992.. These workers show that a hierarchy of micro-sized fractures and microcavities Ž0.05–20 m m in width. are related to coal lithotypes. That is, bright coals contain mainly microfractures and dull coals contain mainly microcavities. These workers demonstrated that the size, continuity, and connectivity of these microstructures play a significant role in the permeability and flow of methane through the coal reservoir. Thus, methane flow in the coal reservoir is governed by these microstructures Žmicroporosity. and the accompanying macrostructures Žmacroporosity. that make up the cleat system. Harpalani and Chen Ž1992. investigated, in the laboratory, the relationship of these dual-porosity roles in coals. Their investigation focused on the behavior of the strain Žby volume. on the coal matrix Žwith the microstructures. and its effect on the intervening cleat system. They demonstrated that as the coal matrix volume decreases Žshrinkage. with desorption as methane pressure decreases, the cleat Žfracture. porosity or aperture increases, which, in turn, leads to increasing permeability of the coal. Permeability in the coal reservoir may be enhanced by acid leaching of secondary minerals as demonstrated in the laboratory by Paterson et al. Ž1992.. Although permeability decreases at depth ŽFig. 11., gas content increases but finally levels off at depth ŽMcKee et al., 1986.. Thus, the ‘rule of thumb’ for methane exploration should be at least from 152 m Ž500 ft. below the surface to 1830 m Ž6000 ft. at depth ŽFig. 12.. The enhanced reservoir characteristics in combination with other properties such as hydrology, coal thickness and continuity,

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Fig. 12. Relationship of permeability and depth Žsee shaded area. for coal seams in some coal basins in the United States Žmodified from McKee et al., 1986..

basin-coalfield geology, and well completion and stimulation contribute to the producibility of coalbed methane ŽDurucan et al., 1992; Ellard et al., 1992; Tyler et al., 1992; Waller, 1992.. 4. Summary Although the detrimental effects of coalbed gas on mining and development has been known for more than 100 years, harnessing the associated coalbed methane as an energy resource is still in its infancy. Release of coalbed gas during underground mining and its migration into the network of tunnels or mine workings have been the focus of investigations because of safety and productivity. This research towards safe and productive mining has led to understanding the origin, mechanism, prediction, and prevention of coalbed gas outbursts and explosions. These studies also have led to the methane drainage technology that is now applied to commercial recovery of coalbed gas. Control and management of this vented gas and the ‘energy crises’ of the mid 1970’s gave rise to commercial exploitation of coalbed methane 25 years ago. Since then, there have been concentrated research efforts directed towards the origin, accumulation, distribution, availability, and recoverability of coalbed methane. Advances in multidiscipline researches in coal mining and geology have truly moved coalbed methane from a mining hazard to a new energy resource. References Ammosov, I.I., Eremin, I.V., 1960. Fracturing in coal, IZDAT Publishers, Office of Tech. Services, Washington, DC, 100 pp, translated from Russian, 1963.

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21

Amuedo, C.L., Bryson, R.S., 1977. Trinidad-Raton Basins: model coal resource evaluation program. In: Murray, D.K. ŽEd.., Geology of Rocky Mtn. Coal., vol. 1, Colo. Geol. Survey Resource Ser., pp. 45–60. Anderson, S.B., 1995. Outbursts of methane gas and associated mining problems experienced at Twistdraai colliery. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 423–434. Beamish, B.B., Crosdale, P.J., 1995. The influence of maceral content on the sorption of gases by coal and the association with outbursting. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 353–362. Bibler, C.J., Marshall, J.S., Pilcher, R.C., 1998. Status of worldwide coal mine methane emissions and use. Int. J. Coal Geol. 35, 281–308, this volume. Birukov, Y., 1995. Regional monitoring conception of rock mass properties and conditions. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp 169–170. Bobrov, I.A., 1995. Investigations of the relationship between acoustic signal spectrum characteristics and state of mining rock mass. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 133–138. Bodziony, J., Nelicki, A., Topolnicki, J., 1990. Investigations of experimental generation of coal and gas outburst. In: Litwiniszyn, J. ŽEd.., Strata as Multiphase Medium. Rock and Gas Outbursts. Krakow: Wydawnictwo AGH, pp. 489–508. Campoli, A.A., Trevits, M., Molinda, G.M., 1985. Coal and gas outbursts: prediction and prevention. Coal Min. 4p., reprinted. Chen, X., Barron, K., Chan, D., 1995. A few factors influencing outbursts in underground coal mines. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 39–48. Cheng, C., Ding, Y., 1971. A preliminary study of gas outbursts. Proceeding of the International Symposium on Mining Technology and Science. China Inst. of Min. and Tech., pp. 35–42. Bodziony, J., Kraj, W., 1995. Investigations of instantaneous outbursts of coal and gas in laboratory condition. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 31–38. Christianovich, S.A., 1953. Outbursts of gas and coal. Izv. AH SSR Otd. Tech. Nauk. 12, 1689–1999. Christianovich, S.A., Salganik, B., 1983. Several basic aspects of the forming of sudden outbursts of coal Žrock. and gas. 5th Congress International Congress on Rock Mechanics, Melbourne, pp. E41–E50. Clark, I.H., Boyd, G.L., 1995. Geologic controls on coalbed methane accumulations. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 369–374. Close, J.C., 1993. Natural fractures in coal. In: Law, B.E., Rice, D.D. ŽEds.., Hydrocarbon from Coal, Amer. Assoc. of Petrol. Geol. Studies in Geol., No. 38, pp. 119–132. Colombo, U., Gazzarrini, F., Gonfiantini, R., Kneuper, G., Teichmuller, M., Teichmuller, R., 1970. Carbon isotope study on methane from German coal deposits. In: Hobson, G.D., Speers, G.C. ŽEds.., Advances in Organic Geochemistry, 1966. Oxford, Pergamon Press, pp. 1–26. Dai, J., Qi, H., Song, Y., Guan, D., 1987. Composition, carbon isotope characteristics and the origin of coalbed gases in China and their implication. Sci. Sin. B 30, 1324–1337. Davies, A.W., Styles, P., Jones, V.K., 1987. Developments in outburst prediction by microseismic monitoring from the surface. Min. Eng. 147, 486–498. Decker, A.D., Davis, T.L., Klawitter, A.J., 1992. A case history of fracture detection methods used to locate open fractures in coal. In: Beamish, B.B., Gamson, P.D. ŽEds.., vol. 2, Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, pp. 51–74. Deguchi, G., Yu, B., Jiao, J., 1995. JapanrChina research co-operation on prevention of gas outbursts. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 139–146. Deul, M., 1964. Methane drainage from coalbeds: program of applied research: Proceedings of 60th Meeting, Rocky Mtn. Coal Min. Inst., pp. 54–60. Deul, M., Kim, A.G., 1986. Methane control research: Summary of results, 1964–80. US Bureau of Mines Bull., vol. 687, 174p.

22

R.M. Floresr International Journal of Coal Geology 35 (1998) 3–26

Diamond, W.P., Bodden, W.R., Zuber, M.D., Schraufnagel, R.A., 1989. Measuring the extent of coalbed gas drainage after 10 years of production at the Oak Ridge pattern, Alabama. Proceedings of the 1989 Coalbed Methane Symp. Tuscaloosa, AL, pp. 185–193. Diamond, W.P., 1994. Methane control for underground coal mines. US Bur. of Mines, Info. Circ. 9395, 44p. Dolly, E.D., Meissner, F.F., 1977. Geology and gas exploration potential, upper Cretaceous and lower Tertiary strata, northern Raton Basin, Colorado. In: Veal, H.K. ŽEd.., Exploration Frontiers of the Central and Southern Rockies. Rocky Mtn. Assoc. Geol. Symp., pp. 247–270. Dunn, B.W., 1984. Coal as a conventional source of methane: a review analysis of a 312 well production area in the Mary Lee coal seam in Tuscaloosa County, Alabama: SPE 1983, SPErDOErGRI 12875. Dunn, B.W., 1995. Vertical well degasification in advance of mining – a potential gas management method for reducing gas emissions and outbursts. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 267–275. Durie, R.A., Hawkins, P.J., Kukla, G.T., 1992. The Galilee basin coal measures: A potential methane resource? – A case for a well planned, integrated exploration and R and D programme. In: Beamish, B.B., Gamson, P.D. ŽEd.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 1, pp. 81–97. Durucan, S., Creedy, D.P., Edwards, J.S., 1992. Geological and geotechnical factors controlling the occurrence and flow of methane in coal seams. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 2, pp. 33–50. Ellard, J., Roark, R., Ayers, W.B., Jr., 1992. Geologic controls on coalbed methane production: an example from the Pottsville Formation ŽPennsylvanian age., Black Warrior Basin, Alabama, USA. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 1, pp. 45–62. Ettinger, I., Eremin, I., Zimakov, B. and, Yanovskaya, M., 1966. Natural factors influencing coal sorption properties. I-petrography and sorption properties of coals. Fuel 45, 267–275. Fails, T.G., 1996. Coalbed potential of some Variscan foredeep basins. In: Gayer, R., Harris, I. ŽEds.., Coalbed methane and coal geology, Geol Soc., Spec. Pub. No., vol. 109. pp 13–26. Faiz, M.M., Aziz, N.I., Hutton, A.C., Jones, B.G., 1992. Porosity and gas sorption capacity of some eastern Australian coals in relation to coal rank and composition. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 4, pp. 9–20. Flores, R.M., Stricker, G.D., Bader, L.R., 1997. Stratigraphic architecture of the Tertiary alluvial Beluga and Sterling Formations, Kenai Peninsula, Alaska. In: Karl, S., Vaughn, N., Ryherd, T. ŽEds.., Kenai Peninsula Field Guidebook, Alaska. Geol. Soc., pp. 36–53. Flores, R.M., Roberts, S.B., Perry, W.J., Jr., 1994. Paleocene paleogeography of the Wind River, Bighorn, and Powder River Basins, Wyoming. In: Flores, R.M., Mehring, K.T., Jones, R.W., Beck, T.L. ŽEds.., Organics and the Rockies field guide, Wyo. State Geol. Surv., Pub. Info. Circ. No. 33, pp. 1–16. Freeman, V.L., 1979. Preliminary report on rank of deep coals in part of the southern Piceance Creek Basin, US Geol. Survey Open-File Rept. 79-725, 10p. Freudenberg, U., Schulter, L.S., Schutz, R., Thomas, K., 1996. Main factors controlling coalbed methane distribution in Ruhr District, Germany. In: Gayer, R., Harris, I. ŽEds.., Coalbed methane and coal geology. Geol Soc., Spec. Pub. No. 109, pp. 67–88. Gamson, P.D., Beamish, B.B., 1992. Coal type, microstructure and gas flow behaviour of Bowen Basin coals. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 4, pp. 43–66. Gawor, M., Meier, E.A., Rysz, J., 1991. Experimental research on the rarefaction waves with the mixture of crushed coal and gas: Twenty Years Cooperation in Physics and Fluids, Gottingen-Krakow, pp. 81–103. Gayer, R., Harris, I., 1996. Coalbed methane and coal geology. Geol Soc., Spec. Pub. No. 109, 344p. Gimm, W.A.R., Pforr, H., 1964. Breaking behavior of salt rock under rock bursts and gas outbursts, Proc. of the 4th Inter. Conf. on Strata Control and Rock Mechanics, pp. 434–449. Gotoh, K., Matsui, K., Takemaru, Y., Li, Z.K., 1995. A theory of mechanics of coal and gas outburst. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 25–30.

R.M. Floresr International Journal of Coal Geology 35 (1998) 3–26

23

Gray, I., 1991. Gas from Australian coals: Where from where to. In: Bamnerry, W.J., Depers, A.M. ŽEd.., Proc. of Symposium on Gas in Australian coals. Geol. Soc. of Australia. Symp. Ser. 2, pp. 31–40. Hanes, J., 1995. Outbursts in Leichhardt colliery: lessons learnt. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 445–449. Hatherly, P., Murray, W., Stickley, G., Eisler, P., Tchen, T., 1995. Development of in-seam borehole logging tools for detection of outburst prone structures. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 93–100. Hargraves, A.J., 1983. Instantaneous outbursts of coal and gas – A review. Proc. Austr. Inst. Min. Metall. 285, 1–37. Harpalani, S., Chen, G., 1992. Effect of gas production on porosity and permeability of coal. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 4, pp. 67–78. Higgs, M.D., 1986. Laboratory studies into the generation of natural gas from coals. In: Brooks, J. ŽEd.., Habitat of Paleozoic Gas in N.W. Europe, Geological Publication, vol. 23, pp. 113–120. Hobbs, R.G., 1978. Methane occurrences, hazards, and potential resources: Recluse geologic analysis area, northern Campbell County, Wyoming: US Geological Survey Open-File Rept. 78-401, 20p. Humphrey, H.B., 1960. Historical summary of coal-mine explosions in the United States, 1810–1958. U.S. Bur. Mines Bull., vol. 586, 280p. ICF Resources, 1990. The United States coalbed methane resource. Quart. Review of Methane from Coal Seams Tech., 7, 10–28. Hunt, J.M., 1979. Petroleum geochemistry and geology, Freeman, W.H. and Co., 617p. Janas, G., 1985. Neue Erkenntnisse auf dem Gebiete der Ausgasungvorausberechung: Glukauf, Forschungshefte 01 Žin German.. Juch, D., 1996. Assessment of West German hardcoal resources and its relation to coalbed methane. In: Gayer, R., Harris, I. ŽEds.., Coalbed methane and coal geology. Geol. Soc., Spec. Pub. No. 109, pp. 59–66. Juntgen, H., Karweil, J., 1966. Gasbilbung un gasspeicherung im steinkohlenflozen, Part I and II: Erdol Kohle–Erdgas–Petrochemie, vol. 19, pp. 251–258, pp. 339–344 Žin German.. Kemp, J.H., Petersen, 1988. Coalbed gas development in the San Juan Basin, New Mexico and Colorado: A primer for the lawyer and landman. In: Fassett, J.E. ŽEd.., Geology and coalbed methane resources of the northern San Juan Basin, Colorado and New Mexico, Rcky. Mtn. Assoc. Geol., 257–280. Khodot, W.W., 1961. Mechanism of coal and gas outbursts: Collection of Papers on the 20th Anniversary of the Institute of Mining, USSR Academy of Science: Wydawnictwa Gorniczy, Warsaw. Koenig, R.A., Bocking, M.A., Forster, I., Enever, J.R., Casey, D.A., 1992. Experience with well testing and in-situ stress measurement in the Sydney Basin for evaluation of coalbed methane prospectivity. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia, James Cook Univ. of No. Queensland, vol. 2, pp. 75–96. Kotarba, M., 1990. Origin of gases accumulated in upper Carboniferous coal-bearing strata of Lower Silesian coal basin and southern part of Rybnik coal district. Rock and Gas Outburst 1, 37–49. Kotarba, M., 1988. Geochemical criteria for the origin of natural gases accumulated in the Upper Carboniferous coal-seam-bearing formations in Walbrych Coal Basin: Stanislaw Staszio Academy of Min. and Metall. Scientific Bull. 1199, 11. Kozlowski, B., 1980. Gas and coal outburst hazard in coal mining, PWN, Warsaw, Poland. Lama, R.D. ŽEd.., 1995. Management and control of high gas emissions and outbursts in underground coal mines International Symp. Cum. Workshop: Westonprint in Kiama Wollongong, NSW, Australia, 618p. Law, B.E., 1992. Thermal maturity patterns of Cretaceous and Tertiary rocks, San Juan Basin, Colorado and New Mexico. Geol. Soc. Amer. Bull. 104, 192–207. Law, B.E., Rice, D.D. ŽEds.., 1993. Hydrocarbons from coal, Amer. Assoc. Petrol. Geol. Studies in Geol., No. 38, 400p. Law, B.E., Rice, D.D., Flores, R.M., 1991, Coalbed gas accumulations in the Paleocene Fort Union Formation, Powder River Basin, Wyoming. In: Schwochow, S.D., Murray, D.K., Fahy, M.F. ŽEds.., Coalbed Methane of Western North America. Rocky Mtn. Assoc. of Geol., pp. 179–190. Levine, J.R., 1992. Influences of coal composition on coal seam reservoir quality: A review: In: Beamish,

24

R.M. Floresr International Journal of Coal Geology 35 (1998) 3–26

B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia, James Cook Univ. of No. Queensland, vol. i, pp. i–xvii. Levine, J.R., 1991. The impact of oil formed during coalification on generation and storage of natural gas in coal bed reservoir system, 3rd Coalbed Methane Symp. Proc., Tuscaloosa, AL, pp. 307–315. Levine, J.R., 1987. Influence of coal composition on the generation and retention of coalbed natural gas, Proc. of the 1987 Coalbed Methane Symp., Tuscaloosa, AL, pp. 15–18. Litwiniszyn, J., 1995. State of the art on the mechanism of outbursts in coal mines. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 1–14. Litwiniszyn, J., 1987. Gas emission from a crushed rock medium during its sudden outbursts. Archives of Min. Sciences: 32, 155–168. Loiret, J., Laligant, G., 1923. Allgemeirner bericht zusammenfassung dertatsachen und beachtungen und richtlinien fur gruben mit gasausbruchen, Reichskohlenrat. Tagebuch No. 171, p. 7.30 Žin German.. Machisak, J.C., Wrenn, V.E., Jones, N.L., Reid, E.J., Rice, D.D., 1961. Injury experience in coal mining, 1959. U.S. Bur. Mines IC 8067, 61p. Mahtab, M.A., 1982. Geochemical aspects of gas outbursts in Louisiana salt mines. Assoc. Eng. Geol. Bull. 19, 389–400. Majewska, Z., 1990. Acoustic emission of coal during sorption of CO 2 . Rock and Gas Outburst 1, 221–232. Mallett, C.W., Russell, N.J., 1992. The thermal history of Bowen – Gunnedah – Sydney Basins. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia, James Cook Univ. of No. Queensland, vol. 1, pp. 75–80. McKee, C.R., Bumb, A.C., Way, S.C., Koenig, R.A., Reverand, J.M., Brandenburg, C.F., 1986. Using permeability vs depth correlations to assess the potential for producing gas from coal seams, Methane From Coal-Seams Tech., pp. 415–26. Meissner, F.F., 1984. Cretaceous and lower Tertiary coals as sources for gas accumulations in the Rocky Mountain area. In: Woodward, J., Meissner, F.F., Clayton, J.L. ŽEds.., Hydrocarbon source rocks of the greater Rocky Mountain region, Rocky Mtn. Assoc. Geol., pp. 401–431. Merritt, R.D., Hawley, C.C., 1986. Map of Alaska’s coal resources. Alaska Div. Geol. and Geophys. Surv. Spec. Rept., vol. 37, 1 sheet, scale 1:2,500,00. Moyer, F.T., Jones, N.L., 1968. Injury experience in coal mining. U.S. Bur. Mines IC 8389, 88p. Mroz, Z., Zacharski, A., 1990. Coal layer deformation and rock-gas outburst initiation, Rock and Gas Outburst., vol. II, pp. 537–570. Murray, D.K., 1996. Anthracite: A promising new target for coalbed methane exploration. Amer. Assoc. Petrol. Geol. Bull. 80, 976. Nathan, S., Anderson, H.J., Cook, R.A., Herzer, R.H., Hoskins, R.H., Raine, J.I., Smale, D., 1986. Cretaceous and Cenozoic sedimentary basins of the West Coast region, South Island, New Zealand. Sci. Infor. Publ. Centre, DSIR, Wellington, NZ, 90p. Noack, K., 1995. Control of high gas emissions in underground coal mines. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines, Westonprint, Kiama, NSW, Australia, pp. 15–24. Nuccio, V.F., Finn, T.M., 1994. Structural and thermal history of Paleocene Fort Union Formation, central and eastern Wind River Basin, with emphasis on petroleum potential of the Waltman Shale Member. In: Flores, R.M., Mehring, K.T., Jones, R.W., Beck, T.L. ŽEds.., Organics and the Rockies Field Guide. Wyo. State Geol. Surv. Pub. Info. Circ., No. 33, pp. 53–68. Okten, G., Biron, C., Saltoglu, S., Ozturk, M., 1995. Gas and coal outbursts of Zonguldak coalfield of Turkey and preventive measures. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines, Westonprint, Kiama, NSW, Australia, pp. 459–464. Paterson, L., Meaney, K., Smyth, M., 1992. Measurements of relative permeability, absolute permeability and fracture geometry in coal. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 4, pp. 79–78. Perry, W.J., Jr., Flores, R.M., 1997. Sequential Laramide deformation and Paleocene patterns in deep gas-prone basins in the Rocky Mountain region. In: Dyman, T., Wescott, W.A., Rice, D.D. ŽEds.., Geologic Controls of Deep Natural Gas Resources in the United States, US Geol. Surv. Bull., 2146-E, pp. 49–59.

R.M. Floresr International Journal of Coal Geology 35 (1998) 3–26

25

Pontolillo, J., Stanton, R.W., 1994. Vitrinite reflectance variations in Paleocene and Eocene coals of the Powder River, Williston, Hanna, Bighorn, and Bull Mountain basins, USA. The Soc. for Org. Petrol. Abst. with Progs., pp. 82–84. Rightmire, C.T., 1984. Coalbed methane resource. In: Rightmire, C.T., Eddy, G.E., Kirr, J.N. ŽEds.., Coalbed Methane Resources of the United States, Am. Assoc. Petrol. Geol. Studies in Geology Ser., No. 17, pp. 1–13. Rightmire, C.T., Eddy, G.E., Kirr, J.N., ŽEds.., 1984. Coalbed Methane Resources of the United States. Am. Assoc. Petrol. Geol. Studies in Geology Ser., No. 17, 378p. Rice, D.D., 1993. Composition and origins of coalbed gas. In: Law, B.E., Rice, D.D. ŽEds.., Hydrocarbons from coal, Amer. Assoc. Petrol. Geol. Studies in Geol., No. 38, pp. 159–184. Rice, D.D., 1992. Controls, habitat, resource potential of ancient bacterial gas. In: Vitaly, R. ŽEd.., Bacterial gas, Editions Technip., pp. 91–118. Ryncarz, T., 1989. Stress and strain distribution around borehole drilled in a gas bearing coal seam prone to sudden outbursts. Archives of Min. Sci. 34, 29–45. Ryncarz, T., 1990. Stresses in coal induced by gas content changes. Rock and Gas Outburst II, 469–486. Seto, M., Katsuyama, K., 1995. Estimation of hydrofractures in coal measures using acoustic emission. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 161–168. Sergeev, I.V., Ivanov, B.M., 1995. Complex methods to determine zones liable to sudden outbursts during prospecting. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 79–84. Sherwood, A.M., 1986. An outline of the geology of New Zealand coalfields, New Zeal. Geol. Surv. Record 15 ISSN 0112 465X, 27p. Skow, M.L., Kim, A.G., Deul, M., 1980. Creating a safer environment in US coal mines. U.S. Bur. of Mines, Spec. Pub., 50p. Smith, T.N., 1995. Coalbed methane potential of Alaska and drilling results for the upper Cook Inlet Basin, Intergas ’95, Proceedings of Symposium, May 15–19, 1995, The Univ. of Alabama, Tuscaloosa, AL, 21p. Smith, J.W., Pallaser, R.J., 1996. Microbial origin of Australian coalbed methane. Amer. Assoc. Petrol Geol. Bull. 80, 891–897. Soot, P.M., 1988. Non-conventional fuel tax credit. In: Fassett, J.E. ŽEd.., Geology and coal-bed methane resources of the northern San Juan Basin, Colorado and New Mexico. Rcky. Mtn. Assoc. Geol., pp. 253–255. Stricker, G.D., 1993. Coalbed methane in Alaska – is this a viable alternate resource for s state with abundant conventional energy supplies?. Focus on Alaska Coal ’93. Mineral. Industry Resear. Lab., Univ. of Alaska, p. 6. Stricker, G.D., 1991. Economic Alaskan coal deposits. In: Gluskoter, H.J., Rice, D.D., Taylor, R.B., ŽEds.., Economic Geology, US Geol Soc. Amer., The Geol. of North Amer. P-2, pp. 591–602. Styles, P., 1995. Harmonic tremor seismic precursors and their implications for the mechanisms of coal-gas outbursts. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 123–132. Suggate, R.P., 1959. New Zealand coals. New Zeal. Dept. Sci. Indus. Res. Bull. 134, 113. Talebi, S., Mottahed, P., Corbett, G.R., 1995. Outburst monitoring using microseismic techniques in the Phalen colliery, Sydney, Nova Scotia, Canada. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 153–160. Tarnowski, J., 1995. Calculations concerning coal and gas outbursts. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 49–61. Tarnowski, J., 1988. A comparative method for prognosticating coal and gas outburst hazard zones: How do those forecasts agree with the actual state in variable geological conditions, 12th International Meeting on the Ways on Coping with Rock and Gas outburst Hazard in Underground Mining, Radkow, pp. 19–23. Topolnicki, J., 1995. Energy balance in an outburst. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 67–74. Ting, F.T.C., 1977. Origin and spacing of cleats in coal beds. J. Pressure Vessel Tech. 99, 624–626. Tyler, R., Kaiser, W.R., Ambrose, W.A., Laubach, A.R., Ayers, W.B., 1992. Coalbed methane characteristics

26

R.M. Floresr International Journal of Coal Geology 35 (1998) 3–26

in the foreland of the Cordilleran Thrust belt, western United States. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 4Ž2., pp. 11–32. Tyler, R., Kaiser, W.R., Scott, A.R., Hamilton, D.S., 1997. The potential for coalbed gas exploration and production in the Greater Green River Basin, southwest Wyoming and northwest Colorado. The Rocky Mtn. Geol. 34, 7–24. Vance, W.E., Cave, M., 1992. Coalbed gas in New Zealand. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 4, pp. 31–44. Waller, S.F., 1992. A successful operating company’s perspective of the key constraints upon profitable coalbed methane development. In: Beamish, B.B., Gamson, P.D. ŽEds.., Symposium on Coalbed Methane Research and Development in Australia. James Cook Univ. of No. Queensland, vol. 4, pp. xxix–lv. Zabourdyaev, V.S., 1995. Gas content forecasting methods for mine developments, gas content reduction means and prevention of sudden gas and coal outbursts. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 229–236. Zhang, G., 1995. Area prediction of danger of coal and gas outburst – example of application in Jiaozuo mining area in China. In: Lama, R.D. ŽEd.., Management and Control of High Gas Outbursts In Underground Coal Mines. Westonprint, Kiama, NSW, Australia, pp. 195–200. Zhang, Y.G., Chen, H.J., 1985. Concepts on the generation and accumulation of biogenic gas. J. Petrol. Geol. 8, 405–422.