Creat membership Creat membership
Sign in

Forgot password?

Confirm
  • Forgot password?
    Sign Up
  • Confirm
    Sign In
home > search

Now showing items 1 - 16 of 72

  • Reservoir properties of Chinese tectonic coal: A review

    Cheng, Yuanping   Pan, Zhejun  

    Tectonic coal, formed after the intact coal being subjected to long-term intense squeezing, shearing and deformation, is characterised by brittle or ductile damaged coal body, with the characteristics of low cohesion, low strength and low permeability. Most of the outburst accidents in China occurred in tectonic coal seams due to the difficulties in gas drainage. In this review article, reservoir properties, including pore structure, adsorption, diffusion, permeability and geomechanical properties of the tectonic coal are reviewed in detail and compared with those of the intact coal, as these properties are important for gas drainage. It was found that tectonic coal in general shows larger total pore volume and specific surface area than intact coal for larger pores due to tectonism, however, no significant difference is observed in smaller pores due to the combined opposing effects of metamorphism and tectonism. Diffusion coefficient of tectonic coal is generally higher than that of intact coal, and tectonic coal typical has higher adsorption capacity than intact coal. Compressive strength and elasticity modulus are smaller for tectonic coal than intact coal. Field permeability of tectonic coal is obviously lower than that of intact coal, which is on the contrary to the experimental results from laboratory. It was found that using reconstituted samples for tectonic coal in the laboratory is the main cause for this discrepancy between field and laboratory observations. It is suggested that more work is required on tectonic coal and a few research areas are proposed for future research.
    Download Collect
  • The effect of a tectonic stress field on coal and gas outbursts.

    An, Fenghua   Cheng, Yuanping  

    Coal and gas outbursts have always been a serious threat to the safe and efficient mining of coal resources. Ground stress (especially the tectonic stress) has a notable effect on the occurrence and distribution of outbursts in the field practice. A numerical model considering the effect of coal gas was established to analyze the outburst danger from the perspective of stress conditions. To evaluate the outburst tendency, the potential energy of yielded coal mass accumulated during an outburst initiation was studied. The results showed that the gas pressure and the strength reduction from the adsorbed gas aggravated the coal mass failure and the ground stress altered by tectonics would affect the plastic zone distribution. To demonstrate the outburst tendency, the ratio of potential energy for the outburst initiation and the energy consumption was used. Increase of coal gas and tectonic stress could enhance the potential energy accumulation ratio, meaning larger outburst tendency. The component of potential energy for outburst initiation indicated that the proportion of elastic energy was increased due to tectonic stress. The elastic energy increase is deduced as the cause for a greater outburst danger in a tectonic area from the perspective of stress conditions. =20
    Download Collect
  • Experimental study on the interactions of supercritical CO2 and H2O with anthracite

    Zhang, Kaizhong   Cheng, Yuanping   Wang, Liang  

    To better understand the mechanism of interactions of supercritical CO2 (SCCO2) and H2O, untreated, SCCO2 treated and SCCO2-H2O treated anthracites were adopted to analyze changes in pore structure, adsorption capacity. Observations from experimental data reveal that mineral and other substances in the fractures and matrix of coal body are dissolved and mobilized by the carbonic acid formed from the mixture of SCCO2 and H2O, which may contribute to smaller pore development and enhance the adsorption capacity. These findings may provide new insights into effective and safe storage of CO2 in coal reservoir.
    Download Collect
  • Effects of coal rank on physicochemical properties of coal and on methane adsorption

    Cheng, Yuanping   Jiang, Haina   Zhang, Xiaolei   Cui, Jiaqing   Song, Cheng   Li, Xuanliang  

    Download Collect
  • Gas transport through coal particles:Matrix-flux controlled or fracture-flux controlled?

    Zhao, Wei   Wang, Kai   Liu, Shimin   Cheng, Yuanping  

    In laboratory measurements, methane ad-/de-sorption behavior on coal is known to be directly related to the particle size. As expected, coal exhibits a relatively high initial desorption rate for smaller coal particles which results in a different gas desorption volume and pressure curves from platter ones for larger coal particles. Both fracture-dominated and matrix-dominated flow theories had been proposed to explain the difference in shapes of desorption curves. These two theories, however, are contradictory to each other and neither of them is completely convincing. Based on the newly developed relationship of apparent diffusion coefficient and apparent permeability, this work uses a dual-permeability concept to explain the different shapes of desorption curves. Numerical simulation solutions indicate that the switching dominance of the fracture and matrix permeability systems produces variable desorption curve shapes. With continuing decrease of coal particle size, the flow will gradually change from fracture-dominated to matrix-dominated mode. The critical apparent permeability ratio dividing the domination of these two systems is in the order of similar to 10(2), in contrast to the initial hypothesis that if one system dominates the overall gas flow, its permeability must be smaller than that of the other. As particle radius decreases, this parameter first increases and then remain at a certain value. At last, the simulated desorption curves were validated with laboratory desorption experimental data.
    Download Collect
  • Gas diffusion in coal particles:A review of mathematical models and their applications

    Zhao, Wei   Cheng, Yuanping   Pan, Zhejun   Wang, Kai   Liu, Shimin  

    As key flow properties for coalbed methane production, greenhouse gas reduction through CO2 storage in coal and gas drainage to improve mining safety, knowledge of gas diffusion in coal has attracted significant interest. In the past decades, numerous efforts have been made to study the nature of gas diffusion in coal both experimentally and theoretically, and many models, including analytical and empirical models, have been proposed. However, because the assumptions, simplifications and applications of these models differ greatly, it is essential to critically review, compare and classify them for better use in practice. Therefore, this article reviews the state of the art on the gas diffusion in coal particles from the aspects of definition, mathematical models, experimental methods, and applications in environment, energy and mining safety areas. Moreover, this review article also dedicates to investigate the inter-relationships between different models, classify them into different categories and identify their limitations when they are applied in different areas. Based on these analyses, the potential research areas related to gas diffusion in coal are proposed.
    Download Collect
  • Analysis and Prediction of Gas Recovery from Abandoned Underground Coal Mines in China

    Li, Wei   Su, Er-Lei   Cheng, Yuanping   Zhang, Rong   Liu, Zhengdong   Younger, Paul L.   Pan, Dongming  

    Mine closures are likely to become especially widespread in eastern China. However, because of relatively high residual coal-bed methane content, the abandoned coal mine methane (ACMM) reserves of China are huge, and from a greenhouse gas-control perspective it is preferable that they be developed and utilized rather than allowed to vent to the atmosphere. The exploitation and development of ACMM in China is still in its infancy, with theory and practice undergoing rapid development. Four factors are particularly influential in the design of ACMM recovery strategies. The first factor is what may be termed the "enrichment space," which reflects the final state of the strata after completion of longwall extraction and subsequent strata settlement and is here defined as the region between the outer limit of stress relief and the limit of the extracted panels. Quan-titative analysis of the components of gas mixtures recovered from the enrichment space can be tracked using stable carbon isotope techniques. The second factor is the permeability field surrounding the abandoned mine voids. The thick mudstones that commonly overlie the coal seams serve to confine the water and gas within the enrichment space and old mine voids. The geometry of these confining layers can be confirmed by seismic reflection or other geophysical methods, which can reveal the extent of the zone affected by fracture development. On this basis, models of methane movement in abandoned mines can be constrained, allowing valuable predictions of availability of ACMM resources under different mining and post-closure drainage conditions.
    Download Collect
  • Gas diffusion in coal particles: A review of mathematical models and their applications

    Zhao, Wei   Cheng, Yuanping   Pan, Zhejun   Wang, Kai   Liu, Shimin  

    Download Collect
  • Experimental investigation on coal pore and fracture characteristics based on fractal theory

    Guo, Haijun   Yuan, Liang   Cheng, Yuanping   Wang, Kai   Xu, Chao  

    Coal is an extremely complex porous medium. To study the pore and fracture characteristics of coal, samples from northeastern China were collected and crushed into eight kinds of particle sizes to conduct the experiments using a combination of basic physical parameters, mercury intrusion porosimetry (MIP) and N-2 (77 K)/CO2 (273 K) adsorption pore structure characterization. At the same time, the scale characteristics of the coal pores and fractures were analyzed by fractal theory. The results indicate that the pores and fractures in coal become increasingly simpler and are more favorable for gas storage and migration during the crushing of the coal samples. The fractal curves of the pores and fractures in coal samples with different particle sizes determined from MIP were all divided into two parts by an inflection point. According to fractal theory, the width that corresponds to the inflection points of the fractal curves are considered to be the critical value for determining the pores and fractures in coal. On this basis, the matrix porosity and the fracture porosity in coal were obtained by combining the data from the MIP and N-2 (77 K)/CO2 (273 K) adsorption. It is believed that this study is of great significance to analyze the coal permeability evolution law affected by the dual-porosity coal structure characteristics. (C) 2019 Elsevier B.V. All rights reserved.
    Download Collect
  • Experimental investigation on coal pore and fracture characteristics based on fractal theory

    Guo, Haijun   Yuan, Liang   Cheng, Yuanping   Wang, Kai   Xu, Chao  

    Download Collect
  • Unsteady-State Diffusion of Gas in Coals and Its Relationship with Coal Pore Structure

    Guo, Haijun   Cheng, Yuanping   Yuan, Liang   Wang, Liang   Zhou, Hongxing  

    Coalbed methane (CBM) is under consideration as a potential energy resource because of its global abundance. The exploitation and development of CBM depends on the correct characterization of coal structure and gas migration properties. In this paper, four coal samples with different degrees of metamorphism were collected from the northern China mining area. The gas desorption properties of these samples were studied using a modified gas desorption experimental setup. A nonconstant diffusion coefficient (non-CDC) model was introduced to analyze the gas diffusion properties. In addition, both mercury intrusion porosimetry (MIP) and low-pressure nitrogen gas adsorption (LP-N(2)GA) were used to investigate the coal pore structure. The results indicate that gas desorption and diffusion vary significantly in coal samples with different degrees of metamorphism and that the non-CDC model could accurately describe gas diffusion in coal. In bituminous and anthracite coal, gas desorption and diffusion abilities increased with the increasing degree of metamorphism, but both properties were greater in lignite coal. Comparing the pore structure characteristics and the gas desorption and diffusion properties showed that lignite's particular pore structure resulted in a higher gas adsorption capacity than for high-volatility bituminous coal. The initial desorption and diffusion in lignite were also greater than in medium-volatility bituminous coal or anthracite coal. These results suggest that lignite has significant potential for CBM exploitation and development.
    Download Collect
  • New insights into the CH4 adsorption capacity of coal based on microscopic pore properties

    Hu, Biao   Cheng, Yuanping   He, Xinxin   Wang, Zhenyang   Jiang, Zhaonan   Wang, Chenghao   Li, Wei   Wang, Liang  

    The objective of this study is to quantitatively describe the CH4 adsorption capacity of coal through microscopic pore properties. In this work, the micropore volume distributions (MPVDs) of granular coal samples from six collieries were obtained by low-pressure CO2 adsorption (LPGA-CO2), and the external specific surface areas (SSAs) were calculated using low-pressure N-2 adsorption (LPGA-N-2). Based on micropore filling and monolayer coverage theories, the micropores were assumed to be cylindrical to obtain the distribution of CH4 in pore structures with different scales. For the coal samples used in this study, micropores were common, whose SSAs accounted for most of the total SSAs (90.39-99.58%), and the micropore volumes accounted for 75.61-96.55% of total pore volumes. The quantity of CH4 adsorbed in the form of micropore filling account for 74-99% of the total amount adsorbed, while the amount of CH4 adsorbed by micropores in the size range of 0.38-0.76 nm was 38-55% of the total amount adsorbed and accounted for the largest proportion in the nine adsorption areas partitioned according to the number of CH4 molecules occupying micropores with different scales. Based on a combination of the high-pressure CH4 adsorption (HPGA-CH4) results, the estimated Langmuir volumes are in close agreement with the measured Langmuir volumes, which demonstrates that the CH4 adsorption capacity of the coal is determined by both the accessible MPVD and external SSAs. The results of this study may be significant for understanding the pore networks and the CH4 adsorption mechanism in coal under in situ conditions.
    Download Collect
  • Is the long-term sequestration of CO2 in and around deep,abandoned coal mines feasible?

    Li, Wei   Ren, Tian-wei   Su, Er-lei   Cheng, Yuanping  

    Many of the largest fixed sources of CO2 emissions are major power stations located on or very close to major coalfields. Even when local coal reserves are exhausted, coal- and/or biomass-fired power generation often persists at such sites, as they occupy pivotal positions in the national power grids that developed around them. To date, strategies for CO2 sequestration from such power plants have focused on long-distance transport by pipeline to depleted hydrocarbon reservoirs and similar deep saline aquifers. Yet where abandoned coal mines extend more than about 800m below ground level, the void space represented by the old mine voids themselves, and roof strata that have been rendered more permeable by void collapse, could represent convenient auxiliary loci for CO2 sequestration. Furthermore, the geochemical nature of coal and coal-bearing strata may offer mechanisms for entrapment of injected CO2 in or on the solid phase that are not available in potential storage zones considered to date. Engineering evaluation of this possibility requires consideration of the likely fate of CO2 in free, adsorbed, dissolved, and mineralized forms, and of the geotechnical integrity of enclosing strata and abandoned mine infrastructure that could serve as seals to trap injected CO2 in place. A protocol for assessing these factors has been developed, based on critical evaluation of mining records, hydrogeological conditions, and geotechnical data, resulting in a quantitative assessment of the capacity for CO2 sequestration represented by deep abandoned coal mine workings. Preliminary application of the decision logic is illustrated for the Daning coal mines in China.
    Download Collect
  • Influence of thermal metamorphism on CBM reservoir characteristics of low-rank bituminous coal

    Jiang, Jingyu   Zhang, Qiang   Cheng, Yuanping   Jin, Kan   Zhao, Wei   Guo, Haijun  

    As mining depths increase, new challenges have emerged, such as abrupt changes in coalbed methane (CBM) reservoir rules and gas outbursts, particularly in coal/sill contact metamorphism zones. To investigate the influence of magmatic-contact metamorphism on CBM reservoirs, fifteen samples were selected from the N(1)708 coalface in the Daxing Mine at different distances from a sill in the Tiefa Coalfield, China. This sill-form intrusive body had a positive effect on the properties of the CBM reservoir. The thermal effect of the igneous sill remoulds the pore structures of thermally metamorphosed coal (TMC). More generally, the seepage pores (pores >100 nm) and the surface areas of the TMC samples were more developed than those of the unaltered samples, suggesting that contact metamorphism might have significant implications for the excellent gas flow/adsorption capacity of TMC. The Langmuir volume of TMC sample #3 was measured as 36.1 m(3)/t. TMC samples showed higher initial desorption rates and lower moisture; in sample 2, the proportion of gas desorbed (cumulative volume/total volume) reached almost 0.5 in only 90 s. The diffusion coefficients (D) for four TMC samples were within the range 1.41 x 10(-11)-2.59 x 10(-10) m(2)/s. These results show that the high initial gas desorption rate and low moisture of the TMC have a positive influence on gas diffusion and CBM drainage, but lead to high gas outburst index. The gas content and gas pressure beneath the sill were obviously greater than those in the unaltered coals. The CH4 levels of TMC were slightly higher than those of the unaltered samples. However, approaching the sill, it is significant that CO2 levels showed an obvious increase. It is postulated that the higher CO2 levels of TMC are likely derived from the breakdown of calcium carbonate under high-temperature conditions. These results indicate that the TMC covers dual gas (CH4 and CO2) outburst potential, thus gas pre-drainage before mining is necessary in contact metamorphism zones. (C) 2016 Elsevier B.V. All rights reserved.
    Download Collect
  • Effect of Water Invasion on Outburst Predictive Index of Low Rank Coals in Dalong Mine.

    Jiang, Jingyu   Cheng, Yuanping   Mou, Junhui   Jin, Kan   Cui, Jie  

    To improve the coal permeability and outburst prevention, coal seam water injection and a series of outburst prevention measures were tested in outburst coal mines. These methods have become important technologies used for coal and gas outburst prevention and control by increasing the external moisture of coal or decreasing the stress of coal seam and changing the coal pore structure and gas desorption speed. In addition, techniques have had a significant impact on the gas extraction and outburst prevention indicators of coal seams. Globally, low rank coals reservoirs account for nearly half of hidden coal reserves and the most obvious feature of low rank coal is the high natural moisture content. Moisture will restrain the gas desorption and will affect the gas extraction and accuracy of the outburst prediction of coals. To study the influence of injected water on methane desorption dynamic characteristics and the outburst predictive index of coal, coal samples were collected from the Dalong Mine. The methane adsorption/desorption test was conducted on coal samples under conditions of different injected water contents. Selective analysis assessed the variations of the gas desorption quantities and the outburst prediction index (coal cutting desorption index). Adsorption tests indicated that the Langmuir volume of the Dalong coal sample is ~40.26 m3/t, indicating a strong gas adsorption ability. With the increase of injected water content, the gas desorption amount of the coal samples decreased under the same pressure and temperature. Higher moisture content lowered the accumulation desorption quantity after 120 minutes. The gas desorption volumes and moisture content conformed to a logarithmic relationship. After moisture correction, we obtained the long-flame coal outburst prediction (cutting desorption) index critical value. This value can provide a theoretical basis for outburst prediction and prevention of low rank coal mines and similar occurrence conditions of coal seams. =20
    Download Collect
  • Stress evolution and coal seam deformation through the mining of a remote upper protective layer

    Tu, Qingyi   Cheng, Yuanping  

    Protective layer mining is considered to be an effective method to resolve the outburst risk of coal seams, but limited theoretical and experimental results exist for remote upper protective layer mining. To study the effect of the remote upper protective layer mining, a case study of the Renlou Coal Mine is selected. The stress evolution in the protected layer is analyzed using Flac(3D) and is verified by the measurement of coal seam deformation and investigation of the unloading boundary. The results indicate that remote upper protective layer mining induces an unloading of stress within the protected layer, while a stress concentration occurs outside of the unloading area. The coal seam deformation is consistent with the stress evolution, for which the maximum compressional and expansional deformation are 0.5 parts per thousand and 7.19 parts per thousand, respectively. The gas pressure decreases significantly as a consequence of these applications, following which the gas pressures within the theoretical unloading boundary are 0.30 MPa and 0.35 MPa along-strike and along the tendency of the protected layer, respectively.
    Download Collect
1 2 3 4 5

Contact

If you have any feedback, Please follow the official account to submit feedback.

Turn on your phone and scan

Submit Feedback