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Estimation of Coal Gas Content Using Geostatistical Methods in GIS Environment: A Case Study From Tabas Coal Mine
Abstract
Coal gas content is one of the most effective parameters in safety and productivity of mechanized mining system. This gas can be explosive when it reaches a certain percentage of the mine air, i.e. lower explosive limit (LEL). Hence, knowledge about the coal gas content before exploitation operation is so necessary. This study uses geostatistical estimator to predict gas content of coal seams. First in this study, core data from 33 exploration boreholes in Tabas coal mine were gathered. Having preprocessed the quality of data and the absence of isotropy, Universal Kriging method was chosen as the best estimation method. Using estimation evaluation criteria, the best model among exponential, spherical and Gaussian model was selected. The map of gas content was plotted using of ArcGIS. Results showed that approximately 4% of total study area has the gas content less than 5 m3/ton, and 7% between 5 and 10 m3/ton. Meanwhile, in about 57% of total area, gas content more than 15 m3/ton was predicted.
... Through the pre-analysis of the main influencing factors of gas content or pressure, the analytic algorithm, multiple linear regression (MLR), artificial neural networks, and other methods can achieve satisfactory results (Wei et al. 2009;Dai 2016;Li et al. 2019;Wang et al. 2019). Some scholars use geostatistics method to estimate the gas content of coal seam under GIS environment, which also has a certain effect (Vaziri et al. 2015). ...
Thin coal seams in mines usually lack gas data. Thus, preventing and controlling gas outbursts of thin coal seams are difficult. In this study, a coal structure index, which is used to express the damage degree of coal, was estimated by logging curve. In accordance with the contour line of the floor of the coal seam, structural curvature was calculated to express the complexity of the coal seam structure quantitatively. Subsequently, relationships among the burial depth, thickness, coal structure index, structural curvature were analyzed on the basis of the gas pressure of coal seam. The gas pressure values of the coal seams of Nos. 22, 24, and 27 in the study area were predicted by multiple linear regression (MLR) and were then verified and analyzed. The deviation rate of the MLR method was 6.5%–19.7%, with an average of 13.0%. The average deviation rate between the predicted value and the measured value was 11.6%, except for the measuring point of No. 2, which had a large deviation. Results show that the prediction accuracy of the aforementioned method is acceptable and has practical value in the prediction of gas pressure in thin coal seams without measured data. The results in the gas pressure prediction provide a basis for evaluating the risk of gas outbursts in thin coal seams.
... Through the pre-analysis of the main influencing factors of gas content or pressure, the analytic algorithm, multiple linear regression (MLR), artificial neural networks, and other methods, can achieve satisfactory results (Wang et al. 1999;Wu et al. 2008;Yan, 2010;Liu et al. 2012;Sun et al. 2015;Li et al. 2019). Some scholars use geostatistics method to estimate the gas content of coal seam under GIS environment, which also has a certain effect (Vaziri et al. 2015). ...
Thin coal seams in mines lack gas data; thus, gas outbursts of thin coal seams are difficult to prevent and control. In this study, a coal structure index, which is used to express the damage degree of coal, was estimated by logging curve. In accordance with the contour line of the floor of the coal seam, structural curvature was calculated to quantitatively express the complexity of the coal seam structure. Then, the relationships among the burial depth, thickness, coal structure index, structural curvature, with gas pressure of coal seam were analyzed. The gas pressure of coal seam of Nos. 22, 24, and 27 in the study area was predicted by multiple linear regression (MLR) and then was verified and analyzed. The deviation rate of the MLR method was 6.5%–19.7%, with an average of 13.0%. The average deviation rate between the predicted value and the measured value was 11.6%, except for measuring point of No. 2, which had a large deviation. Results show that the prediction accuracy of the above method is acceptable, and it has practical value in the prediction of gas pressure in thin coal seams without measured data. Results of the gas pressure prediction provide a basis for evaluating the risk of gas outbursts in thin coal seams.
... It deserves mention that only in cases where a certain percentage of gas is present in mine atmosphere, the gas explosion occurs. For Tabas coal mine, the permissible limit of methane gas is 1.25 volume percent (Vaziri et al. 2015). The scale of given risks has been selected based on experiences of coal mining reported in the literature as well as during early mined-out panels in the case study. ...
From the viewpoint of safety in underground coal mining, the most suitable mining panel is the one with minimum geological structures, the right machinery, and equipment selection, trained employee, and proficient stope management. Since the ground parameters are uncontrollable and inherent uncertainties exist, a high percent of risk will usually accompany the underground coal mining activities. The main purpose of this study is to present a geological–geotechnical risk assessment model for identification of high risk-prone areas in underground coal mines using an integrated GIS- geostatistics system. Tabas as the first mechanized and largest underground coal mine in Iran was selected as a case study in this study. Gas content of coal seam, Coal Mine Roof Rating (CMRR), initial in situ stress state, fault throw, and orientation were selected as hazard/risk factors. For estimating the amount of coal seam gas content, CMRR and initial in situ stress in unsampled areas and providing the prediction maps, geostatistics module in ArcGIS was used. Rock engineering system–interaction matrix method was used for attribute weight assignment. Next, the attribute layers were weighted, rated, and overlaid to create a final map of geohazards risk. The analysis results of final risk map indicate that about 45% of under study area is prone to high to very high geohazards risk. Comparison of the results with experiences obtained during the early part of the mine and mined-out panels showed generally good agreement with promising ideas. This highlights the potential application of the GIS-based approach for hazards detection and geohazards risk assessment in underground coal mines.
The impact on global climate change from coal mine methane emissions in China has been drawing attention as coal production has powered its economic development. Data on coal mine methane emissions from the State Administration of Coal Mine Safety of China has been analyzed. It is estimated that the methane emission from coal mining in China reached 20 billions of cubic meters in 2008, most of which comes from state-owned coal mines with high-gas content. China releases six times as much of methane from coal mines as compared to the United States. However, Chinese methane emission from coal production accounts for only a very small proportion on the environmental impact when compared to emissions of carbon dioxide from fossil fuel consumption. The Chinese government has shown environmental awareness and resolution on the mitigation and utilization of coal mine methane emissions. Measures have been taken to implement the programs of mitigation and utilization of coal mine methane, and at the same time, to ensure mining safety. Nearly 7.2 billions of cubic meters of methane were drained from the coal mines, and 32% of it was utilized in 2008. The slow advancement of technologies for the drainage and utilization of low-concentration methane from ventilation air hinders the progress of mitigation of atmospheric methane and the utilization of coal mine methane emissions.
The US Geological Survey (USGS) is completing a national assessment of coal resources in the five top coal-producing regions in the US. Point-located data provide measurements on coal thickness and sulfur content. The sample data and their geologic interpretation represent the most regionally complete and up-to-date assessment of what is known about top-producing US coal beds. The sample data are analyzed using a combination of geologic and Geographic Information System (GIS) models to estimate tonnages and qualities of the coal beds.Traditionally, GIS practitioners use contouring to represent geographical patterns of “similar” data values. The tonnage and grade of coal resources are then assessed by using the contour lines as references for interpolation. An assessment taken to this point is only indicative of resource quantity and quality. Data users may benefit from a statistical approach that would allow them to better understand the uncertainty and limitations of the sample data.To develop a quantitative approach, geostatistics were applied to the data on coal sulfur content from samples taken in the Pittsburgh coal bed (located in the eastern US, in the southwestern part of the state of Pennsylvania, and in adjoining areas in the states of Ohio and West Virginia). Geostatistical methods that account for regional and local trends were applied to blocks 2.7 mi (4.3 km) on a side. The data and geostatistics support conclusions concerning the average sulfur content and its degree of reliability at regional- and economic-block scale over the large, contiguous part of the Pittsburgh outcrop, but not to a mine scale. To validate the method, a comparison was made with the sulfur contents in sample data taken from 53 coal mines located in the study area. The comparison showed a high degree of similarity between the sulfur content in the mine samples and the sulfur content represented by the geostatistically derived contours.
Coalbed methane (CBM) is the generic name for all methane of coal seam origin. It is a natural gas formed by geological, or biological, processes in coal seams and generally consists predominantly of methane, but may also contain some higher alkanes and non-combustible gases. Methane is released whenever coal is de-stressed or fractured by mining. Methane is one of the main greenhouse gases contributing to global warming, therefore releasing it to atmosphere is an environmental hazard. However, it is also an important energy resource and can be recovered from operational coal mines, abandoned coal mines, and virgin (unmined) coal seams. Significant volumes of CBM are exploited worldwide for space heating, industrial processes, and power generation. This paper critically reviews the current UK and worldwide status of CBM extraction and utilization technologies building on a previous study funded through the Department of Trade and Industry's Cleaner Coal Technology Programme [1].
In order to characterise the saleable feldspar in a granite deposit, a methodology was developed in accordance with the exploitation process. This consisted of mechanically extracting the surface layer of the batholith and separating the feldspar from the quartz using the granulometric separation method, given that the size of the grains of the feldspar is greater than that of quartz.Following washing, grinding and magnetic separation of the feldspar in order to eliminate the ferromagnesium minerals, the saleable feldspar was characterised in terms of the factors that determine its market value, namely, its content in Al2O3, SiO2, Na2O and K2O.Following the opening of prospecting pits in the granite massif, samples were analysed in the laboratory using three different granulometric cuts and by reproducing the treatment process. The values for the quality variables of saleable feldspar were obtained, and the results were interpolated to the entire deposit using the kriging method.In order to summarise the information from the above-mentioned variables, a quality index was constructed using multivariate statistics and by employing market criteria, and subsequently, the values of the index were interpolated to the entire deposit using bidimensional kriging.The map of saleable quality feldspar from the deposit permits both affirmation of the treatment process yield for each granulometric cut and the planning of extraction from the deposit to obtain a homogeneous quality in the saleable feldspar.
The paper presents the resources and present status of coal-seam methane from the mining field of JSW S.A., as well as trends in its application both in JSW S.A. plants and elsewhere. For the period 1999-2001, the dynamics of growth of methane utilization are shown. Perspectives of methane drainage are considered, with regard to both work and the realization of restructuring programs in the mining industry. Demand and supply of methane are discussed, taking into account real and potential opportunities. An assessment was made of the emissions to the atmosphere both of methane and of other pollutants. An evaluation of the influence exerted by these measures on the performance of cogeneration of heat and electricity has been prepared. Several projects in progress are described, namely the increase of gas-firing in existing boiler installations, investment projects referring to the installation of gas engines for cogeneration of heat and electricity, utilization of the distribution network for the maximum utilization of gas and the designs of power-generation systems (using methane) for air conditioning in the mines.
Gas outburst is recognized as a potentially fatal hazard to be managed during the mining of gassy coal seams. Gas outbursts in Australian coal mines have been associated with the presence of geological structures in the coal and surrounding rocks, having a range of spatial scales from millimetres to metres. The contributing mechanisms are influenced by coal gas reservoir variables including gas composition, fluid pressure, desorption pressure and rate, porosity, intrinsic permeability and relative permeability. They are also influenced by geomechanical variables such as strength, in situ stress and mining-induced stress.
Land evaluation is sensitive to the effects of variability of ecologically complex phenomena. A probability map incorporating some of these phenomena is proposed to account for local uncertainty of areas affected by soil degradation in the Apennines of south Italy. To be useful, a method for assessing soil degradation should integrate several kinds of data. We present here an overview of the geostatistical approach to solving this problem: non-linear estimation. The following factors have been considered: the soil erosion by water (geomorphologic indicator), the station aridity (bioclimate indicator), and top-soil depth (pedologic indicator). We convert the continuous data values of each variable at each location using a binary variable indicator transform based on critical thresholds. The indicator transform values for individual variables are then integrated to form multiple variable indicator transform (MVIT) to evaluate the degree of soil degradation. Areas suited to soil degradation maps delineated by geographical information system (GIS), showed that the joint probabilities of meeting specific criteria indicator Kriging were influenced by the critical threshold values used to transform each individual variable and the method of integration. So, the understanding of soil vulnerability to degradation is increased to providing a way to classify degraded regions. On the basis of this information different land uses strategies could be identified to develop sustainable assessment models of soils. For example, many countries of these disadvantaged areas, should have agro-forestation programmes that increase the heterogeneity in vegetation cover contrasting hydrological properties, thus promoting a self-regulating system for runoff and erosional soil degradation control.
Methane drainage has become an integral part of modern coal mining operations when gas emissions cannot be practically dealt with using conventional ventilation methods alone. Boreholes are often drilled above and below the caving zone and connected to a drainage range located along the return gate. This paper describes the construction and analysis of the results obtained from the two- and three- dimensional geomechanical and gas flow models experienced around an active deep UK longwall coal production panel. The models constructed using the commercial FLAC codes were undertaken to provide information to the ventilation engineers at the mine on the likely gas sources and gas flow paths into the face line areas and gate roads. This information allows for the correct design of the orientation, length and support of the boreholes to maximise gas capture. The paper describes the method adopted to derive the relevant rock mass parameters and the laboratory tests conducted to obtain the stress-dependent permeability of coal measure rock strata. A functional relationship is proposed whereby the intrinsic bulk permeability of a sheared coal measure rock may be predicted from the confining stress. A detailed discussion of the geomechanical modelling methodology and the derivation of the strata permeabilities and gas flow modelling adopted is presented. The output of the models is described and used to interpret the major potential gas sources and pathway into the workings.
The Chinese government has made many energy policies on coal, and coalmine methane (CMM) use. However, not all of these policies have effects or positive impacts. For example, it has been quite a few years since the national government made policies to encourage coalmine methane power to be sold to the grid. Practice showed that not any kilowatt of electricity was sold from a coalmine methane power plant to the grid in Sichuan and Guizhou Provinces as of December 2008. The objectives of this paper are to review and evaluate the Chinese government energy and climate policies that are related to coal and coalmine methane, analyze relevant policy barriers, and make recommendations to overcome these barriers and avoid policy failures. This paper provides the literature review, challenges, resources, policies and other updated information on China's CMM recovery and utilization. The paper concludes that China needs to further reform its energy and environment management system, engage provincial governments in CMM capture and use activities, and provide incentives to qualified engineers and skilled workers to work in remote coal mining areas. This paper transfers key messages to policy makers for them to make better CMM capture and use policies.