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Now showing items 49 - 64 of 72

  • Experimental investigation on the effects of supercritical carbon dioxide on coal permeability:Implication for CO2 injection method

    Li, Wei   Liu, Zhengdong   Su, Erlei   Cheng, Yuanping  

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  • Study on the stress relief and permeability increase in a special low-permeability thick coal seam to stimulate gas drainage

    Zhang, Rong   Cheng, Yuanping   Yuan, Liang  

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  • Experimental Investigation of Pore Structure Damage in Pulverized Coal:Implications for Methane Adsorption and Diffusion Characteristics

    Jin, Kan   Cheng, Yuanping   Liu, Qngquan   Zhao, Wei   Wang, Liang   Wang, Fei   Wu, Dongmei  

    To study the effect of pulverization on coal's pore structure and the implications for methane adsorption and diffusion properties, three kinds of high volatile bituminous coals were sampled and crushed into six kinds of particle sizes to conduct the experiments using a combination of proximate analysis, N-2 (77 K)/CO2 (273 K) adsorption pore structure characterization, and high-pressure methane adsorption and diffusion properties determination. Results indicate that the pulverization process has no remarkable influence on the proximate properties of the coal, while the pore structures are evidently modified. The pulverization process significantly increases the specific surface area and pore volume (measured by N-2 adsorption) of the coal, which favors gas adsorption and diffusion. However, its effects on <2 nm micropore structure (measured by CO2 adsorption) are variable. The high-pressure methane adsorption and diffusion tests demonstrate that the adsorption volume and diffusion quantities both increase with the decrease of coal particle size. The adsorption experiments also indicate that because of the complex adsorption mechanism, the high-pressure adsorption capacities of the coal are comprehensively influenced by the <2 nm micropore (measured by CO2 adsorption) as well as the additional BET specific surface area and pore volume (diameter below 10 nm, measured by N-2 adsorption) that are generated during the pulverization process. Moreover, methane desorption experiments reveal the existence of coal rank -dependent extremity particle size, which can significantly affect the diffusion performance of methane within coal.
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  • Architecture,stress state and permeability of a fault zone in Jiulishan coal mine,China:Implication for coal and gas outbursts

    Li, Wei   Ren, Tianwei   Busch, Andreas   den Hartog, S. A. M.   Cheng, Yuanping   Qiao, Wei   Li, Bin  

    The Mafangquan (MFQ) fault zone, transecting a coal seam in Jiulishan coal mine in Jiaozuo coalfield, Henan Province, China, was investigated in detail in view of coal mining safety, including its architecture, stress and permeability features and implication for coal and gas outburst. 10 boreholes have been drilled for formation testing as well as coal sample retrieval for laboratory analysis. Gas content, Protodyakonov strength, gas emission index and pore volume are tested and analysed at different distances from the MFQ fault. A fault structure that can be separated into three distinct zones, including the fault core, the mylonitized zone and the granulated/cataclastic zone, was identified. In-situ stress tests, numerical simulations and model predictions show a principal stress rotation and fault zone stress regime. It is found that the maximum principal stress has shifted to a lower angle pent to the fault zone extend direction gradually with a destress zone from fault core to the damage zone. The permeability of the fault zone has a correlation to fault zone architecture and stress regimes in the coal seam with a high permeability in the mylonitized coal zone. The coal weakened due to deformation, high pore pressure and stress superimposition have a negative impact on coal and gas outburst. In particular, the stress rotation limits the formation of hydrofractures in the case of high pore pressure and reduces fault zone strength, which may have an orthogonal relation to the mining galleries, favouring coal and gas outburst.
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  • Characterization of pore structure and the gas diffusion properties of tectonic and intact coal:Implications for lost gas calculation

    Wang, Zhenyang   Cheng, Yuanping   Wang, Liang   Zhou, Hongxing   He, Xinxin   Yi, Minghao   Xi, Chuanpeng  

    Accurate calculation of the amounts of lost gas from coal are of great importance in underground mining. In this study, the effects of pore structure and the gas diffusion properties on the lost gas from tectonic and intact coals were investigated by the mercury intrusion porosimetry method (MIP), N-2 (77 K) and CO2 (273 K) adsorption methods, and gas adsorption equilibrium/desorption tests. The results indicated that mesopore and macropore volumes increased after tectonic damage, as did the specific surface areas (SSA) and porosities. However, there was little change for the micropore volumes. Additionally, the desorption experiments indicated that the initial desorption and gas flow capacities of tectonic coal were greater than those of intact coal. Both laboratory and field results demonstrate that there is more higher lost gas for tectonic coal, which is directly influenced by the developed mesopore and macropore structure and by the initial gas desorption capacity. The logarithmic function method is a relatively better choice. When the gas content is determined in coal mines, the sampling exposure times should be kept as short as possible. From the perspective of engineering, this study provides a reference for the calculation of lost gas in tectonic coals. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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  • Quantitative investigation on the structural characteristics of thermally metamorphosed coal:evidence from multi-spectral analysis technology

    Jiang, Jingyu   Zhang, Qiang   Cheng, Yuanping   Wang, Haifeng   Liu, Zhengdong  

    The macromolecule structural characteristics of thermally metamorphosed bituminous coals (TMBC) are very significant to understand the thermal evolution history of coal basin and coal organic maturation. However, the relevant information is still limited. Here, four TMBC, selected from Daxing coal mine, Liaoning province, China, were investigated by using varied modern tools including Fourier transform infrared spectroscopy, X-ray diffraction and Raman spectroscopy to expound the effect of igneous intrusions on their chemical structures. Results indicate that the studied TMBC are characterized as turbostratic structures, composing of crystalline carbon assorted with varying amounts of disordered amorphous carbon. An increase in agglomeration degree of molecular structure in TMBC was observed with the increase in coal ranks. In addition, the strong contact metamorphism imposed on indigenous coal has created new pores and fractures examined by scanning electron microscope, which facilitate the drainage of coal bed methane in coal mines.
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  • Pulverization characteristics of coal from a strong outburst-prone coal seam and their impact on gas desorption and diffusion properties

    Guo, Haijun   Cheng, Yuanping   Ren, Ting   Wang, Liang   Yuan, Liang   Jiang, Haina   Liu, Hongyong  

    Coal seams that are prone to strong outbursts have low strength and cause heavy structural damage to the seam. Their outburst risk is highly related to the release of the adsorbed coalbed gas, which is controlled by the gas desorption and diffusion characteristics of coal. In the Haizi Coal Mine, China, an extremely high gas outburst risk was detected, and the coals from this area were found to have an unprecedented high degree of fragmentation and were present in the pulverized state. To explain the pulverization characteristics of the pulverized coal, the related physical parameters were investigated; the gas desorption and diffusion properties of the pulverized coal were analyzed and compared with those of the unpulverized coal. The results indicated that the pulverized coal could easily reach the required degree of fragmentation for a coal and gas outburst to occur. Furthermore, the pore volume and specific surface area of the pulverized coal differed according to the coal particle size. Compared with the unpulverized coal, the gas desorption and diffusion properties of the pulverized coal were largely varied, and the pore structure of the pulverized coal was much simpler. The formation of pulverized coal is believed to be closely related to complex geological conditions. (C) 2016 Elsevier B.V. All rights reserved.
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  • Effects of diffusion and suction negative pressure on coalbed methane extraction and a new measure to increase the methane utilization rate

    Dong, Jun   Cheng, Yuanping   Jin, Kan   Zhang, Hao   Liu, Qingquan   Jiang, Jingyu   Hu, Biao  

    A constant suction negative pressure is used in coal mines owing to a lack of research on the effects of diffusion and suction negative pressure on methane extraction, resulting in the low methane concentration and utilization rate. In this study, Comsol Multiphysics is used to conduct a numerical solution of a gas-solid coupling model considering pseudo-steady diffusion in coal matrix, seepage in fractures, permeability evolution and coal deformation. The simulation results reveal the methane migration law and the effect of the diffusion process on the methane migration. The role and the influence degree of the suction negative pressure on methane extraction are studied, demonstrating that the suction negative pressure effect weakens gradually with the increasing methane extraction time. The methane concentrations of different suction negative pressures are calculated considering the changing effects of diffusion and suction negative pressure combined with the parallel relation between the methane migration and the air leakage, indicating that reducing the suction negative pressure can effectively increase the methane concentration. To change the present situation of the low methane concentration and utilization rate in coal mines, a new technical measure of methane extraction through parallel boreholes in groups is proposed to adjust the suction negative pressure and increase the methane utilization rate. (C) 2017 Elsevier Ltd. All rights reserved.
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  • Experimental investigation into the damage-induced permeability and deformation relationship of tectonically deformed coal from Huainan coalfield,China

    Liu, Qingquan   Zhang, Kaizhong   Zhou, Hongxing   Cheng, Yuanping   Zhang, Hao   Wang, Liang  

    Knowledge of the mechanical behavior and permeability evolution of tectonically deformed coal (TDC) is the foundation for the successful design of enhanced gas drainage. However, our understanding of the effect of progressive damage on the fluid flow in TDC is limited due to its unique structure and low visibility. We report measurements of the deformation, strength and permeability evolution during triaxial compression of soft coal samples made by TDC. According to the experimental results, the soft coal can generate an obvious nonlinear-elastic deformation before the yield strength, leading to the formation of unique features of the fracture volume evolution of soft coal. The closure of the existing microcracks in soft coal continues until the reversal of the total volume when the confining pressure is greater than or equal to 8 MPa. The fracture compressibility constants of the three soft coal samples were 4.71E-2 MPa-1, 4.63 E-2 MPa-1 and 4.89 E-2 MPa-1, which are much smaller than the literature values reported for other intact coals, which range from 6.21E-2 MPa-1 to 2.71E(-1) MPa-1, indicating that the stress sensitivity of TDC is weaker than that of the intact coal. During the progressive deformation of soft coal, the permeability only reverses when the stress state exceeds the fracture damage stress. The study's achievements show that the simplification of the pre-failure behavior as a perfectly elastic mode is not applicable to the soft coal and would lead to mistakes in further permeability calculations. Further work should be extended to develop a more appropriate constitutive model and a permeability model to describe the pre-failure non-linear (elastic) deformation and the corresponding permeability evolution of soft coal.
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  • Experimental study of pore structure and fractal characteristics of pulverized intact coal and tectonic coal by low temperature nitrogen adsorption

    Wang, Zhenyang   Cheng, Yuanping   Qi, Yuxiao   Wang, Ranpeng   Wang, Liang   Jiang, Jingyu  

    To study the pore structure and fractal characteristics of pulverized intact coal and tectonic coal, proximate analysis, gas adsorption/desorption, and N-2 (77K) adsorption experiments were performed. The results show that micropore, minipore and mesopore volumes, as well as specific surface areas (SSAs), are dependent on the particle size and that they all exhibit a positive correlation with decreasing particle size, a correlation which also promotes gas adsorption. Many complex pores became simpler with the destruction of coal, and some long pores were also converted into short pores; that is, the pore structures of coals (referring to changes in pore shapes and lengths) may become increasingly simple. The mineral matter of samples increases with decreasing particle size and contributes more to the mesopore volume and SSA than to the micropore and minipore volumes. The increased D-1 and reduced D-2 of samples with decreasing particle sizes indicate a greater pore surface roughness and a smaller pore structure anisotropy. Compared with pulverized intact coal, the mineral matter, pore structure and gas adsorption capacity of tectonic coal have significantly increased or decreased. Although they are in the same coal seam, they are no longer the same type. This study of pulverized coal, especially tectonic coal, is of great significance for the further understanding of gas outbursts. (C) 2019 Elsevier B.V. All rights reserved.
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  • Experimental investigation into the damage-induced permeability and deformation relationship of tectonically deformed coal from Huainan coalfield, China

    Liu, Qingquan   Zhang, Kaizhong   Zhou, Hongxing   Cheng, Yuanping   Zhang, Hao   Wang, Liang  

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  • Experimental study of pore structure and fractal characteristics of pulverized intact coal and tectonic coal by low temperature nitrogen adsorption

    Wang, Zhenyang   Cheng, Yuanping   Qi, Yuxiao   Wang, Ranpeng   Wang, Liang   Jiang, Jingyu  

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  • Effects of coal pore structure on methane-coal sorption hysteresis:An experimental investigation based on fractal analysis and hysteresis evaluation

    He, Xinxin   Cheng, Yuanping   Hu, Biao   Wang, Zhenyang   Wang, Chenghao   Yi, Minghao   Wang, Liang  

    To investigate the effects of coal pore structure on the methane-coal sorption hysteresis, six coal samples were collected. The methane-coal sorption measurement was performed at 35 degrees C and pressure up to 5.5 MPa using a high-pressure volumetric analysis system (HPVAS). With the help of N-2 physisorption at 77 K and CO2 physisorption at 273 K, basic pore properties including specific surface area (SSA), mode diameters and pore size distribution (PSD) were obtained through classical thermodynamic methods and the advanced density functional theory (DFT). A Frechet distance index (FDI) based on the resemblance of two curves was proposed to overcome the difficulty in quantitatively evaluating the methane-coal sorption hysteresis. Quantified heterogeneity of the coal pore structure by five fractal dimensions derived from Frenkel-Halsey-Hill model (D-FHH1 and D-FHH2), Neimark-Kiselev model (D-NK), Wang-Li model (D-WL) and Sierpinski model (D-SPS) was coupled with the FDI for regression analyses. Results indicate that increasing SSA and stronger first-layer adsorption energy may exacerbate the methane-coal sorption hysteresis, while no satisfactory correlation was observed between the methane-coal sorption hysteresis and the pore volume. Wider Dubinin-Astakhov PSD and bigger mode diameters were found corresponding to smaller FDIs indicating reduced methane-coal sorption hysteresis. Correlation between the FDI and the fractal dimensions revealed a possible positive correlation between the methane-coal sorption hysteresis and the heterogeneity of the coal pore structure, especially for D-FHH2 whose applied pore widths were 2.78-385 nm.
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  • Influence of Overlying Caprock on Coalbed Methane Migration in the Xutuan Coal Mine,Huaibei Coalfield,China:A Conceptional Analysis on Caprock Sealability

    Zhang, Kaizhong   Liu, Qingquan   Jin, Kan   Wang, Liang   Cheng, Yuanping   Tu, Qingyi  

    In order to determine the controlling factors affecting coalbed gas migration in the Xutuan coal mine, Huaibei Coalfield, China, overlying caprocks with Quaternary and Neogene formation (loose bed), Paleogene formation (Redbed), and coal-bearing strata were investigated via petrography, lithology, and physical properties according to laboratory tests, theoretical analysis, and on-site exploration. Results indicate that the basic properties of coal were not significantly changed whereas the effect of coalbed gas escape was promoted in the presence of Redbed and loose bed. The pore structure analysis shows that Redbed has well-developed pore connectivity than coal-bearing strata (main components are sandstone, siltstone, and mudstone). Also, the diffusion coefficient and permeability of Redbed and loose bed are proved to be a little different than those of sandstone but are much higher than those of mudstone and siltstone. Based on the aforementioned findings, investigation on the sealing mechanism of overlying caprocks on CBM migration was further discussed, interpreting that the thickness, permeation, and diffusion features are crucial factors for sealing capacity of the overlying caprock. Thus, with the simplification on the thickness of overlying strata, a conceptional analysis was carried out to theoretically estimate the sealability of caprocks from surface drilling holes; it appears, though, that the master factor on coalbed methane accumulation is coal-bearing strata instead of Redbed and loose bed with a poor sealability. In this case, the reliability of the evaluation method could be indirectly validated from the on-site gas content data of the actual coal seam to fundamentally reflect the effect of Redbed and loose bed on gas-escaping, and the impact of coal-bearing strata on gas accumulation in the coal seam.
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  • Effect of silica sol on the sealing mechanism of a coalbed methane reservoir:New insights into enhancing the methane concentration and utilization rate

    Hao, Congmeng   Cheng, Yuanping   Dong, Jun   Liu, Hongyong   Jiang, Zhaonan   Tu, Qingyi  

    The low efficiency of coalbed methane (CBM) extraction not only causes a great waste of energy resources and environmental pollution but also poses potential safety risks during coal mining. The main reasons for these issues are the weak borehole sealing effect and serious air leakage that occur during CBM extraction. Seeking an effective sealing material is the key to improve the efficiency of CBM extraction and to protect the environment. In this paper, to explore ways to break through this bottleneck, the feasibility of silica sol (S.G325) as a sealing material for the boreholes used in CBM extraction was theoretically demonstrated. Scanning electron microscopy (SEM) was used to compare the surface morphological characteristics of S.G325 and some commonly used sealing materials. The performance of these materials after sealing the pores/fractures in the methane reservoir was also evaluated using mercury intrusion, an helium porosimeter and methane seepage tests. The experimental results indicate that S.G325 has obvious advantages over other materials because of its greater compactness, stability and performance after sealing. Evaluation of the effects of enhancing CBM extraction showed that S.G325 increased the initial concentration of CBM from 60% to 73.5%-82.9%, the amount of time the CBM that can be utilized from 54 d to 99 d -132 d, the volume of utilizable CBM from 3421 m(3) to 4951 m(3) - 5773 m(3), and the utilization rate of CBM increased by 44.7%-62.8% compared with the original utilizable methane volume. In this paper, new insights into the improvement of energy resource utilization and protection of the environment are shown.
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  • Evaluation of the remote lower protective seam mining for coal mine gas control:A typical case study from the Zhuxianzhuang Coal Mine,Huaibei Coalfield,China

    Jin, Kan   Cheng, Yuanping   Wang, Wei   Liu, Haibo   Liu, Zhengdong   Zhang, Hao  

    The protective seam mining technology is the most effective and economical method in realizing the safe mining of outburst-prone coal seams. To study the effects of remote lower protective seam mining on coal mine gas control, a typical case (average layer spacing: 78 m) taken from the Zhuxianzhuang Coal Mine was investigated by a comprehensive evaluation through numerical simulation, gas extraction data statistics, residual gas pressure/content measurements and recovering gas emission analysis. The results indicate that after the recovery of the protective seam, the unloading effects could lead to a maximum expansion deformation rate of the protected seam by 33.4%o, which remarkably increases the permeability of the coal seam by 4320 times. Combining with the pressure-relief gas extraction methods, considerable amount of the gas (about 78.58%) was extracted from the protected seam, resulting in the maximum residual gas pressure and content of 0.26 MPa and 4.29 m(3)/t respectively, which indicate that the outburst risk has been completely eliminated. Additionally, among the gas extraction methods, the penetrating borehole extraction presents the best drainage effect, accounting for 42.58%-55.09% of the total extracted pressure-relief gas. The effect of the surface wells extraction is closely related to the number of wells and whether the wells can work properly or not. However, the effect of interception boreholes extraction is poor and the extracted amount is almost negligible. Moreover, a protected range extension phenomenon is noticed, which demonstrate that the protected area generated by the protective seam mining is larger than that of the theoretical predicted one, and thus a further study is needed. (C) 2016 Elsevier B.V. All rights reserved.
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