Methane Content Of Coal Seams Research Articles

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

Экспресс-метод и десорбометр для определения газового давления и содержания метана в угольном пласте

Экспресс-метод и десорбометр для определения газового давления и содержания метана в угольном пласте

Issues and options for reducing methane emission to the atmosphere from Indian coal mining

India has a reserve of about 190 billion tonnes of coal spread over nearly 50 coalfields that range in size from a few Km 2 to 1500 Km 2. There are about 440 working mines which produced 238 million tonnes of coal in the year 1992–1993 and methane emission to the atmosphere during the year is estimated to be 0.4 million tonnes. Based on geologic and reservoir characterisation of different coal basins, mine conditions and mining methods and in-situ methane content of coal seams, potential for reduction of methane emission from Indian coal mining is assessed. The exhaust ventilation air of most of the mines has been observed to contain less than 0.02% of methane, utilisation of which may not be economically viable with the currently available technologies. Recovery of methane from gob wells has also limited applications in Indian mines working mostly by bord and pillar method of mining at shallow depths. However, coalbeds in some virgin zones located mainly in the eastern part of the country appear to have appropriate geologic conditions, aggregate seam thickness and gas in place and are likely to be promising sites for pre-mining degasification which will have significant contribution to the reduction of methane emission, increasing mine safety and towards an useful fuel resource for energy.

Methane in the Upper Silesian Coal Basin (Poland) - Problem of Reserves and Exploitation: ABSTRACT

The Upper Silesian Coal Basin (USCB) is the best recognized and the most productive coal basin in Poland. The USCB is primarily defined by the extent of Carboniferous coal-bearing formations. The sedimentary fill displays the stratigraphic record of major progressive inversion phases of the entire Moravo-Silesian basin during the late and post-geosynclinal period of the Variscan orogeny. According to the last estimates the coal reserves occurring above the depth limit of 1500 in are as follows: documented reserves - 58 billion tons, prognostic reserves - 46 billion tons, total - 104 billion tons. The coal type is predominantly vitrinitic, and ash content is reported to be in the range of 11-17% and average sulphur content is 1.13%. The rank of USCB coal is largely controlled by complex coalification processes. It ranges from high volatile bituminous B, through medium volatile bituminous to high rank special coal semi anthracite and anthracite. The methane content of coal seams in USCB varies in a very broad range of 0-22 m{sup 3}/t coal (dry, ash free basis). The average gas content increases considerably within the depth range 600-1000 in from 0.99 to 4.68 m{sup 3}/t coal (daf). In deeper horizons it is more or lessmore » stable varying within the range of 4.7-7.0 m{sup 3}/t coal (daf). By this estimate, on average, the methane content is about 12,5 m{sup 3}/ton. There are several estimates of coal-bed methane resources in the USCB based on different methods. The resources are as follows: documented deposits in active mines to 1000 m: 370 BCM, undeveloped deposits to 1000 in: 340 BCM, deposit between 1000 and 1500 m: 590 BCM, total: 1300 BCM. The coalbed gas from this basin is primarily composed of saturated hydrocarbons and Nitrogen which amount to 97 volume percent. The rest is dominant by Carbon dioxide and Hydrogen.« less

Mathematical modeling of methane flow in a borehole coal mining system

Safety in coal mining is greatly increased by the drainage of the methane content of coal seams through boreholes, simultaneously producing significant energy. The design of suitable drainage technology is based on the mathematical modeling of methane flow in coal seams. In the calculation of the methane pressure, the new mathematical model presented in this paper considers both the sorption phenomenon of methane depending upon the methane pressure and the fact that the variation in methane pressure can create a change in the stress condition of the rock and, as a consequence of this, a change in the permeability of the coal. The new mathematical model can be used for the numerical simulation of the flow processes in coal seams and methane drainage technology can be designed more accurately.

A new approach to the determination of methane content of coal seams

An approach to the determination of methane content of coal seams is proposed. The method utilizes the transformed Airey's empirical equation on desorption of methane from coals. The methane content values estimated by this method correspond well with actual values from laboratory experiments. In the case of Indian coals, the applicability of the $$\sqrt t$$ relationship for the calculation of the gas lost from coal lumps during long periods of time loss appears to be limited due to poor agreement with the experimental values.