Methane Content Of Coal Seams Research Articles

Безопасность высокопроизводительных очистных забоев в метанообильных шахтах

The experience of degassing coal seams using underground boreholes is summarized, scientifically based schemes and parameters of degassing coal seams and the mined out space with directional boreholes in extended excavation areas of shallow coal mines are proposed. The initial gas-dynamic parameters of the excavation area were determined according to the permissible methane content of the breakage face by the gas factor, the methane content of the coal seam in the zone of its excavation by the combine. The lower limit of the methane-bearing capacity of the mined seam, at which preliminary degassing of the coal mass is necessary, is scientifically justified. The dependences of the natural methane content of coal seams on the depth of their occurrence in the conditions of Kuzbass and Vorkuta coal deposits, the effect of natural degassing of the formation by a breakage face, the determining role of degassing by drilling long directional boreholes along the mined and converged coal seams at the excavation areas of high-performance mines, the use of the provisions of the industrial regulations of the integrated technology of extraction and utilization of mine methane are experimentally established as well as forecasts of the absolute methane content of the stoping area by the sources of methane release during the coal extraction.

Дегазация сближенных угольных пластов направленной трассы скважинами

The technology of conducting degassing operations at the mines of Russia is determined by the experience of many years of using means of extracting methane from coal seams and worked-out spaces by drilling wells on coal seams under development, on converged layers, mainly under-worked, unloaded by a working face from rock pressure. The parameters of the degassing of methane release sources at the extraction areas of coal mines were determined based on the results of scientific studies of the processes of methane release into degassing wells and mine workings, methane content of coal seams, gas content of workings, extraction modes of captive methane-air mixtures, their gas composition, suitability for disposal. The dependences were established related to the methane content of coal seams on the yield of volatile substances, gas recovery indicators, and the rate of reduction of methane release during the operation of wells drilled in the plane of the coal seam at high-performance coal mines. The analysis of the results of the operation of coal mines in Russia was carried out, where the degree of methane extraction based on degassing and gas suction at mining sites was 760 m3/min or 54 % of all methane at 193 exploited sites. In 30 areas where degassing was used, this figure reached 1050 m3/min (75 % of the total). At the same time, the flow rate of captured methane was 365 m3/min, including 237 m3/min (60 %) at 6 mines. Studies of degassing parameters of the converged coal seams were carried out in mining areas where the development workings are separated from the mined-out space of the entire coal. In areas of mining operations with high methane release from undermined coal seams, a complex of underground degassing schemes was applied using long directional wells drilled from a local working with its horizontal part brought into the plane of the adjacent seam. The technology, performance and parameters of degassing are determined taking into account the mining conditions of occurrence and mining of coal seams, and the provisions of the regulatory instructions.

Geological and Mining Factors Controlling the Current Methane Conditions in the Rydułtowy Coal Mine (Upper Silesian Coal Basin, Poland)

Methane emissions into mine workings and the atmosphere are still a significant environmental and work safety problem. Since 2000, the Rydułtowy coal mine, located in the western part of the Upper Silesian Coal Basin, has been struggling with significant methane emissions compared to the previous period. The distribution of the methane content in coal seams was analysed, and the factors that influenced it were reviewed. Then, the annual variability in methane emissions in mining excavations was investigated, and the depth of coal extraction was linked to methane conditions and the time of mining works. It has been shown that the currently observed distribution of methane in coal seams is the result of, inter alia, the geological development of the western part of the basin, the lithological character of coal-bearing Carboniferous deposits and overburden, and fault tectonics. The sorption capacity of coal seams decreases with increasing temperature and the coal rank. The amount of methane emitted into mine workings depends mainly on the methane content in the coal seams in mining sites and on the sorption capacity of the coal seams. The depth of exploitation, increasing from year to year, leads to an increase in the methane content in coal seams and a simultaneous decrease in the sorption capacity of coal, which will result in higher methane emissions in the future.

Experimental and Numerical Simulation of Water Adsorption and Diffusion in Coals with Inorganic Minerals

The study on the adsorption and micropore filling of water vapor in coal is significant for predicting coalbed methane content in coal seams. The primary purpose of this study is to explain the effects of coal pore structure and its surface chemistry on water vapor monolayer adsorption, micropore filling, and diffusion coefficient. First, X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) analyzed inorganic mineral components of two kinds of coal samples and pore fissures structures. Then, we divide pores and fissures according to the theory of fractal dimensions. Furthermore, we carried out the water vapor adsorption and desorption experiments on two kinds of coal; in particular, we set 14 points of relative pressure between 0 and 0.2. Guggenheim–Anderson–de Boer (GAB), Frenkel–Halsey–Hill (FHH), and Freundlich models were used to analyze the data of water vapor adsorption to obtain the boundary pressure points of the monolayer, multilayer adsorption, and capillary condensation. Finally, the parameters of the models were obtained by fitting the adsorption data of water vapor according to the combined GAB, Freundlich, DA, and bidisperse adsorption (BDA) models to analyze the interaction mechanism between coal and water. We explain why the strongly adsorbed water minerals, such as pyrite, illite, and nacrite coal, can improve water vapor’s adsorption and diffusion capacity in coal pore fissures.

Multi-scale structural inheritance of fracture systems pattern in coal-bearing measures of the Lorraine-Saar coal Basin

The Lorraine-Saar Basin (LSB) is one of the major Paleozoic coalfields of Western Europe that has been shapedover two centuries as a heartland of underground coal mining and associated industrial activities in the transborderarea of France and Germany. The Basin still has considerable coal reserves accumulated in numerous laterally continuous coal seams that were affected by processes of thermogenic production of gaseous hydrocarbons during post-Carboniferous burial and related coalification. The LSB stands out by its up to 6 km sedimentary column and its inversion resulting in Paleozoic erosion in the range of 750 m (French part of the Basin) and pre-Mesozoic (Permian) erosion between 1800 and 3000 m (German part of the Basin). Historically, coal production in the Lorraine and the Saar portions of the entire Basin was associated with numerous mining hazards because of the high methane content in coal seams. The LSB has the potential to host an enormous unconventional resource base including coalbed methane (CBM). Coal mines here are no longer operated to produce coal; however, methane generated in deep compartments is venting here via fracture swarms to the Earth’s surface. Cutting natural methane emissions throughout CBM production within coal-bearing terrains is a crucial opportunity for slowing global warming rates. Nearly all CBM plays worldwide are affected in some way by natural multiscale fracture sets ranging from large fault zones to closely spaced joints, micro-shears, or cleat sets in coal seams. The LSB is not excluded indeed from this trend because of the long-term experience of geological exploration during extensive coal mining in the past. Characterization of structural patterns of fracture networks at different scales is a pragmatic process boosting the reliable perception of the performance of coalbed methane gas reservoirs. The focus of this contribution is to get an insight into the style and kinematic description of the multi-scale fault and cleat patterns in the LSB based on results of subsurface and underground geological mapping, and X-ray computer tomography. It will benefit the right mindset to ensure proper technical decisions for efficient exploration and exploitation of CBM reservoirs in the Basin.

The Determination of the Methane Content of Coal Seams Based on Drill Cutting and Core Samples from Coal Mine Roadway

The determination of methane content of coal seams is conducted in hard coal mines in order to assess the state of methane hazard but also to evaluate gas resources in the deposit. In the world’s mining industry, natural gas content in coal determination is usually based on direct methods. It remains the basic method in Poland as well. An important element in the determination procedure is the gas loss that occurs while collecting a sample for testing in underground conditions. In the method developed by the authors, which is a Polish standard, based on taking a sample in the form of drill cuttings, this loss was established at a level of 12%. Among researchers dealing with the methane content of coal, there are doubts related to the procedures adopted for coal sampling and the time which passes from taking a sample to enclosing it in a sealed container. Therefore, the studies were designed to evaluate the degree of degassing of the sample taken in the form of drill cuttings according to the standard procedure and in the form of the drill core from a coal mine roadway. The results show that the determinations made for the core coincide with the determinations made for the drill cutting samples, with the loss of gas taken into account.

Forecast methane content in coal seams from -250 m to -400 m of Mong Duong coal mine

Methane is considered to be the most dangerous gas in underground mining coal mines, and is particularl especially dangerous for mines ranked high in methane such as Mao Khe, Quang Hanh, Khe Cham, Mong Duong.... Mong Duong coal mine is tending to exploit down to -400 m and will zone mining areas in 2022, which means that the methane content in the coal seams also tends to increase with the mining depth, especially for the level below -250 m of Mong Duong coal mine, where has relatively complicated geological conditions and very limited methane exploration works. In order to have effective preventive measures to avoid methane gas explosions, the paper has made predictions for the methane storage capacity of Mong Duong coal mine at different depths. The paper has built the prediction chart of methane concentration when exploiting deeply based on the least squares method of Excel software. From there, the forecast data of methane content in coal seams from the current mining depth to -400 m level of Mong Duong coal mine. The forecast results of the methane content in coal seams at -400 level of Mong Duong coal mine are markedly increased compared to the current exploitation level, especially at I12 with increased methane content in the coal seam, maximum reached 4.5828m3/T.kc. The methane content in reservoir I-12 is shown by the equation y = 0.0132x-0.6983. The results of the prediction of methane content make it easier to proactively plan to eliminate methane incidents and ensure safety in underground coal mining.

Methane emissions against the background of natural and mining conditions in the Budryk and Pni\xf3wek mines in the Upper Silesian Coal Basin (Poland)

The paper presents the variability of hard coal output, methane content and methane emissions into coal workings and into the atmosphere from the two most methane-gassy coal mines in Poland. The Budryk mine is one of the youngest mines in Poland, but it is the most methane-gassy as well. In 2016, the total CH4 emissions exceed 140 million of m3. This large increase in methane emissions to mine workings is primarily related to the increase in the depth of coal extraction (up to 1290 m) and, consequently, the rapid increase in the methane content in coal seams (up to 10–12 m3/Mg coaldaf). On the other hand, in the Pniówek mine, methane emission was the highest at the beginning of the study period (1986–1991). During the following years, emission decreased to the values of less than 140 million of m3, which were still one of the largest amounts of emitted methane in the entire Upper Silesian Coal Basin. The coexistence of natural factors, such as the geological structure and gas distribution, as well as mining-related factors, i.e. the depth of mining, the intensity of coal extraction determines the temporal variability of methane emissions in the studied mines.

Experimental study of seismic action influence on gas permeability of coal and hydraulic fractures

Mine field development of coal deposits is currently associated with work at depths exceeding 400m. Under these conditions the gas content of promising horizons is one of the main factors constraining the pace of development. An integral part of gas-bearing coals’ extraction is their preliminary degassing. The methane recovery ratio affects the efficiency and safety of longwall work. Degassing is intensified in order to achieve the required values of methane content in coal seams. A well-known method employed to intensify filtration processes in fluid-saturated rocks is the elastic vibrations’ treatment. The laboratory tests and field work show the positive effect of elastic vibrations on the intensification of methane desorption from coal. Modern works in this field are devoted to investigation of connections between the parameters of vibration action and the degree of increase in the methane desorption. This paper provides the results of a series of experimental studies on seismic action’s effect on the permeability of coal and hydraulic fractures. The research has been carried out on a custom designed laboratory bench. The design of the stand provides the effect of elastic vibrations of small amplitude with independent regulation of the average and differential gas pressures, axial and lateral compression of the sample. The experiments have been carried out using solid coal cores, cores with single through longitudinal cracks simulating drainage hydraulic fractures and cores with the single fractures propped with a low-density proppant designed to intensify the degassing of coal seams. The patterns of the seismic impact on the gas permeability of coal under the conditions of all-round compression have been established in accordance with the results of experiments. Also, the experimental results reveal certain patterns of increase of the drainage cracks’ gas permeability observed when the cracks are propped with proppant and are under the low intensity seismic effect under the conditions of all-round compression. The studies show that the effectiveness of seismic action increases with an increase in the accumulated exposure time, followed by stabilization and persistence of the positive effect for at least 3 - 7 days after the cessation of exposure. The obtained results provide the opportunity to assess the possibility of using seismic action to intensify the degassing of non-propped hydraulic fractures in coal mines.

Study on forecasting methane content in coal seams of Nga Hai mine area

Nga Hai coal mine area has large reserves managed by Quang Hanh Coal Company of Vietnam Mineral Industry Group. In this coal mine, there are 15 coal seams with industrial reserves. Each coal seam contains methane and the deeper it goes down the methane content tends to increase. Nga Hai coal mine is exploiting at-175 level and tends to exploit to-300 level. Currently, the mine is ranked III in terms of methane content in coal seams, while the coal mine is ranked III, which means it is hazardous in terms of the risk of methane fire and explosion. At the time of the methane explosion, Khe Cham coal mine was ranked III for methane. Thus, at present, the Nga Hai coal mine must have strict methane control measures to prevent methane gas fire and explosion like the former Khe Cham coal mine. To have effective methane control options, author took coal samples at the Nga Hai coal mine’s coal seams and analyzed to determine the methane content at different levels. Then author treated data analysis and interpolation methods, the least-squares method to predict methane concentrations at deep levels that cannot be sampled for analysis. With the Forecast of methane content in coal seams, author will provide the mine management company to take proactive measures to avoid the risk of methane gas explosion and take the initiative in mining plans safest and most effective waterfall.

Estimation of Gas Loss in Methodology for Determining Methane Content of Coal Seams

The determination of natural gas content in coal seams is essential to safe mining activities and to estimate gas resources. It is used to estimate methane emissions into workings, which is very important when using preventive measures of methane ignition and explosion. Methane content in a coal seam is mostly determined using a direct method. However, a problem with estimation of gas loss during collecting a sample in a mine occurs in each method. That gas loss is estimated using different procedures. In the Polish mining industry, methane content in a coal seam is mostly determined during roadway advancing faces in coal seams. The differences in procedures for determining methane content in coal in various laboratories gave rise to starting research into developing a new method. This article presents results of study of gas loss unification for the determination of methane content in coal seams. The research focused mainly on determining a uniform method for estimating gas loss using the early adsorption diffusion process. The method of coal sample saturation with methane was used to measure gas desorption rate. Saturation pressures of samples were determined for coal seams in the Upper-Silesian Coal Basin. The analysis of desorption results allowed to determine the dependence between methane content in a coal sample and the initial methane content in a coal seam. It was concluded that the desorption rate was highest within two minutes. For the procedure of coal sampling, gas loss was determined at 12% of both desorbed and residual gases. The presented research results gave rise to developing a uniform method for determining gas content used in Polish coal mining. The method was accepted as the national standard. Methodology using a new gas loss estimation procedure allows for achieving relatively fast results of the determination of methane content in coal seams, which is very important, especially in gassy mines.

Effects of permeability anisotropy on coal mine methane drainage performance

Coal mine methane (CMM) drainage using in-seam boreholes is an effective method to reduce the methane content in coal seams, ensure coal mine safety production and exploit fossil fuel resources. The dominant direction of gas seepage changes due to the anisotropy of coal seam permeability, which causes differences in the amount of methane extracted from boreholes drilled in different directions. The main purpose of this study is to investigate the control effect of coal permeability anisotropy on CMM drainage performance. First, a mathematical model coupling the orthotropic permeability and gas flow in coal seams was established. The methane drainage parameters of the coal mass surrounding in-seam boreholes were simulated. The simulation results showed that the amount of methane extracted from a borehole perpendicular to the permeability advantage direction was much greater than that from a borehole parallel to the permeability advantage direction, and the amount of methane increased with the increase of the angle between the boreholes and the permeability advantage direction. Then, permeability differences of coal samples in three directions, with Gaohe Coal Mine as the test site, were obtained through laboratory tests, and it was determined that the direction of methane flow along the inclined direction of the coal seam was the permeability advantage direction. Finally, five groups of boreholes with different angles from the coal seam inclination, were drilled to investigate their drainage performance. The field test results showed that the group of the largest-angle boreholes had the most positive effect of methane drainage, and the amount of extracted methane was positively proportional to the angle between the borehole and the coal seam inclination. This behavior is consistent with the simulation results. These study outcomes can provide scientific guidance to maximize the methane drainage performance by designing a reasonable layout of boreholes considering the coal permeability anisotropy.

Study of the impact of exploitation structures on pressure distribution and adsorbed methane content in coal seams using dynamic flow models. A case study

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Methane occurrence, emissions and hazards in the Upper Silesian Coal Basin, Poland

The paper presents the variability of methane emissions into mining excavations and the atmosphere in the Upper Silesian Coal Basin (USCB) (Poland) against the background of natural and mining factors. Emissions of methane from exploited coal seams have become a serious problem in the USCB due to the growing methane hazard in coal mines and emissions of methane into the atmosphere. In the mid-nineties 753 million m3 of methane was emitted annually from the USCB mines. Despite a significant drop in coal production over the next 20 years, methane emissions have not decreased sharply; on the contrary, in recent years they have begun to grow, and, in 2016, reached the level of 933 million m3 per year. This represents an increase of 180 million m3 per year since the mid-nineties. One of the important reasons for this phenomenon is the constantly increasing depth of coal exploitation, which in many mines now exceeds 1000 m; this is the depth corresponding to the deep methane zone, where the volume of accumulated methane in the coal seams is particularly high. Factors influencing the volume of methane emissions in relation to mine workings can be divided roughly into two groups: natural (geological) and anthropogenic (mining-related). Natural factors include methane content in coal seams, gas pressure, the presence of free gas in fault zones, related fissures and porous sandstone, the migration of methane through faults and fissures, and the presence of a continuous and impermeable Miocene overburden. Mining factors include the depth of exploitation and the concentration of coal production as expressed in terms of the length, height, and advance of walls. The interdependence of these factors means that, despite the decline in coal production, methane emissions, both total and specific, are increasing. This problem cannot be neglected, especially since it may grow worse in future. One measure to prevent the growth of methane emissions and the associated hazard may be the intensification of mine methane drainage and the economic use of captured mining gas, which is already done in the USCB.

ОЦЕНКА ГАЗОНОСНОСТИ ПЛАСТА К10 В ПРЕДЕЛАХ ШЕРУБАЙНУРИНСКОГО УЧАСТКА КАРАГАНДИНСКОГО УГОЛЬНОГО БАССЕЙНА

Цель: исследование газоносности угольного пласта К10 для оценки ресурсов метана и возможности его добычи на Шерубайнуринском участке Карагандинского угольного бассейна. Методика. Для определения величины природной газоносности угольного пласта К10 Карагандинского угольного бассейна были использованы три методики, основанные на расчетных и фактических данных по газовыделению из пласта при его разработке: 1) расчет газоносности по коэффициентам Лэнгмюра; 2) отбор и обработка проб угля по способу фирмы DMT GmbH & Co. KG; 3) измерение фактического газовыделения. Далее проводилось уточнение указанной величины на основе сравнения результатов, полученных различными способами. Исследования проводились на поле шахты «Абайская» АО «АрселорМиттал Темиртау» при отработке пласта К10. Результаты. Газоносность пласта К10 в пределах Шерубайнуринского участка оценивается в среднем в 17,5 м3/т. Однако способ определения природной газоносности пластов по количеству выделившегося метана дает весьма усредненную величину. Проведенные исследования показали, что результаты определений природной газоносности угольных пластов, выполненных по способу фирмы DMT Gmb&Co, имеют хорошую сходимость с расчётной величиной. Газоносность угольных пластов Шерубайнуринского участка нарастает с глубиной по зависимости, описываемой уравнением регрессии, в общем случае, имеющем вид уравнения Ленгмюра. Результаты исследований показывают, что в практически нетронутом массиве на расстоянии 38…42 м от стенки выработки газоносность постоянна. Научная новизна. Выполнены комплексные исследования газоносности угольного пласта и характера влияния разгрузки на ее величину в Карагандинскомбассейне. Практическая значимость. Сопутствующий добыче угля газ метан при разработке шахт используется для выработки электроэнергии и обеспечения потребностей самой шахты. В будущем на территории Казахстана утилизация угольного метана позволит экономить природный газ и сокращать выбросы парниковых газов. Это перспективный энергетический рынок. Газопроницаемость и метаноносность угольных пластов – это главные критерии оценки метаноугольных площадей при их подготовке к освоению. Исследования газоносности угольных пластов позволят правильно оценивать ресурсы метана и возможности его добычи на Шурубайнуринском участке Карагандинского угольного бассейна

Sampling Methane-Bearing Coal Seams by Freezing Method: Coalbed Methane Desorption and Inhibition Characteristics Under Freezing Temperature

Methane content in coal seam is an essential parameter for the assessment of coalbed gas reserves and is a threat to underground coal mining activities. Compared with the adsorption-isotherm-based indirect method, the direct method by sampling methane-bearing coal seams is apparently more accurate for predicting coalbed methane content. However, the traditional sampling method by using an opened sample tube or collecting drill cuttings with air drilling operation would lead to serious loss of coalbed methane in the sampling process. The pressurized sampling method by employing mechanical-valve-based pressure corer is expected to reduce the loss of coalbed methane, whereas it usually results in failure due to the wear of the mechanical valve. Sampling of methane-bearing coal seams by freezing was proposed in this study, and the coalbed gas desorption characteristics under freezing temperature were studied to verify the feasibility of this method. Results show that low temperature does not only improve the adsorption velocity of the coalbed gas, but also extend the adsorption process and increase the total adsorbed gas. The total adsorbed methane gas increased linearly with decreasing temperature, which was considered to be attributed to the decreased Gibbs free energy and molecular average free path of the coalbed gas molecular caused by low temperature. In contrast, the desorption velocity and total desorbed gas are significantly deceased under lower temperatures. The process of desorption can be divided into three phases. Desorption velocity decreases linearly at the first phase, and then, it shows a slow decreases at the second phase. Finally, the velocity of desorption levels off to a constant value at the third phase. The desorbed coalbed gas shows a parabolic relation to temperature at each phase, and it increases with increasing temperature at the first phase, and then, it poses a declining trend with increasing temperature at the rest phases. The experimental results show that decreasing the system temperature can restrain desorption of coalbed methane effectively, and it is proven to be a feasible way of sampling methane-bearing coal seams.

Methane content of coal seams of Karaganda basin

Methods for studying the natural methane content of coal seams during geological exploration are adequately covered, so the main focus when considering them is landing on those features that are characteristic of the Karaganda basin. The method of studying the qualitative composition of gas in the basin establishes a change in the concentration of methane depending on the geological conditions of the bedding, while it is necessary to find the upper boundary of the methane zone, which is defined as the surface, and the concentration of methane is 80%.

Methane emissions in selected hard-coal mines of the Upper Silesian Coal Basin in 1997–2016

Hard coal is extracted in the Upper Silesian Coal Basin (USCB) from deeper and deeper coal seams every year. In 2000, the average depth of coal extraction was 600 m, in 2010 – 700 m, but in the last two years (2016–2017) this has been extended to a depth of 770 m. The USCB is not homogeneous in layout in terms of methane hazard, but rather very diverse. Therefore, the USCB has been divided into seven gassy regions to show differences in methane danger distribution. Northern and central USCB regions (I, II and III) are the mostly naturally degassed, so the most dangerous gassy conditions are in the IV and V regions, where methane content in coal seams varies from 6 m3/Mg coaldaf to above 18 m3/Mg coaldaf. The two westernmost USCB gassy regions (VI and VII) are poorer in methane than the IV and V areas. Six representative coal mines were chosen: Myslowice-Wesola, Budryk, Brzeszcze, Pniowek, Marcel and Rydultowy-Anna based on their high hard coal production and total methane emissions. The reason for the highest methane emission in those regions might be fault tectonics facilitating methane migration and also the thick and continuous Miocene cover constituting a hermetic screen for gases in the southern part of the USCB.

Estimation of methane content in coal mines using supplementary physical measurements and multivariable geostatistics

The volume of methane that can be released from coal during extraction is usually estimated only on the basis of measurements of methane content in coal seam. Usually, apart from methane measurements, numerous physical variables are also measured before coal extraction. Although physical variables do not produce straightforward information about methane concentration, they can be significantly correlated with it and therefore can also be used in methane content estimation. The goal of this paper was to analyze the possibility of using multivariable geostatistics to estimate methane content in coal seam using physical secondary measurements. To do so, two types of secondary measurements were used: the desorption factor and coal strength index, both of which were used in cokriging and sequential Gaussian co-simulation (SGcoS). Both secondary variables were sufficiently correlated with methane content, validating their use in the analyses. The use of the desorption factor as supplementary data produced an approximately 2% overestimation of values of methane content but only in the vicinity of the geological faults. The overestimation was lower in the case of SGcoS than in the case of cokriging. Application of the coal strength index as a secondary variable did not lead to overestimation. Methods that use supplementary data produced lower kriging variance and simulated standard deviation values of methane content compared to those obtained using kriging and sequential Gaussian simulation (SGS), respectively, where only methane measurements were used. Simulated standard deviations of methane content obtained using SGcoS with a desorption factor were significantly higher than those obtained using SGcoS with the coal strength index used as supplementary data.

Laboratory study of the phenomenon of methane and coal outburst

Gas and rock outbursts occur in virtually all coalfields around the globe [1,2]. Chinese mining has currently been affected by the problem most; nearly one-third of all outbursts take place in China. High levels of outburst threat also occur in Ukraine, Poland, and Australia. Since the phenomenon of outburst is by all means a complex one, its study must be interdisciplinary. It thus involves various aspects of geomechanics, gas study, chemistry, statistics, risk assessment, and many others. In Ref. [3] there are over 30 factors mentioned which might influence outburst threat. Currently, scientists’ views around the world suggest a number of parameters that encourage rock and gas outburst. These are, among others, increased gas capacity of the medium, extremely high diffusivity and increased porosity of coal, and very low gas permeability in natural conditions [4,–6]. According to many authors, coalbed methane capacity constitutes a crucial parameter in the evaluation of outburst and methane threat in coal mines [1]. Methane content in coal seam is not constant; it alters with changes of the properties of coal and of geological conditions in the vicinity of the seam [7,8]. It is assumed that free gas (sorptive unbounded) represents the main source of energy that may lead to destruction of coal structure and the occurrence of rock and gas outburst [9]. The relative amount of free gas in the whole quantity of gas in coal is very important for the assessment of methane and rock outburst threat. The ratio of the free gas quantity to the sorbed gas quantity in the coalbed may vary. Sorptive bounded gas is mainly responsible for the transport of outburst masses [10,11]. Thus it is important in the process of sustaining the outburst. Devising methods of measuring coalbed methane pressure in coal, which would be both effective and reliable, seems to be a significant issue. Various authors [12–14] and others write about