Comprehensive characterization of pore structure in coal seams with abnormal gas emission in deep close range coal seam clusters
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摘要:
煤与瓦斯突出事故一直是煤矿安全生产中的重大问题，煤体中孔裂隙是瓦斯吸附与运移的主要场所，研究孔裂隙结构特征对瓦斯灾害的防控治理具有重大意义。以淮南矿区谢桥矿瓦斯异常涌出煤层煤体为研究对象，对比未发生事故区域及邻近煤层煤体，开展扫描电镜（SEM）、低场核磁共振（NMR）等试验研究，对煤体孔裂隙类型、孔隙连通性、孔径分布、有效孔隙率及渗透率等参数进行研究，探讨煤体孔隙结构对瓦斯吸附及运移的影响。结果表明：煤体孔隙结构必将影响其渗透性，煤体内部碎粒孔大量发育及矿物充填情况严重时不利于流体运移；异常煤层与邻近煤层饱和水煤样核磁共振时间T2谱均发育3个峰，主要以短弛豫时间为主，但各煤体孔径分布及孔隙连通性具有一定差异，异常煤体微孔异常发育，中小孔相对不发育、吸附孔与过渡孔之间连通性差，说明瓦斯运移的差异性与孔径分布和孔隙连通性有关；异常煤体有利于瓦斯吸附不利于瓦斯扩散，且瓦斯放散初速度更大，在受到采动影响时更易发生瓦斯异常涌出或突出事故；煤体微孔占比与有效孔隙率呈负相关关系，中小孔占比与有效孔隙率呈正相关关系，而有效孔隙率与煤体渗透率呈显著线性关系，说明煤体孔径分布是通过影响煤体有效孔隙率，进而影响煤体渗透率；有效孔隙率直接影响煤层渗透率大小，也与煤质参数存在一定关系，在一定程度上可作为评价煤层性质的指标之一。
Abstract:Coal and gas outburst accidents have always been a major problem in coal mine safety production. Pores and fissures in coal are the main places for gas adsorption and migration. It is of great significance to study the structural characteristics of pores and fissures for the prevention and control of gas disasters. Taking the abnormal gas emission coal seam of Xieqiao Coal Mine in Huainan Mining Area as the research object, Compares the areas without accidents and adjacent coal seams conducting experimental studies such as scanning electron microscopy (SEM) and low field nuclear magnetic resonance (NMR) to study the parameters of coal pore and fracture types, pore connectivity, pore size distribution, effective porosity, and permeability, and explores the influence of coal pore structure on gas adsorption and migration. The results show that the internal pore structure of coal body will affect its permeability, and the development of a large number of granular pores in coal body and the serious filling of minerals are not conducive to fluid migration. The T2 spectrum of saturated water coal samples in three regions shows three peaks in nuclear magnetic resonance time, mainly with short relaxation time. However, there are certain differences in the pore size distribution and connectivity of each coal body. The abnormal areas have abnormally developed micropores in the coal body, relatively undeveloped small and medium-sized pores, and poor connectivity between adsorption pores and transition pores, indicating that the differences in gas migration are related to pore size distribution and pore connectivity; The abnormal coal body in the area is conducive to gas adsorption but not conducive to gas diffusion, and the initial velocity of gas release is higher, making it more prone to gas abnormal outburst or outburst accidents when affected by mining; The proportion of micropores in coal is negatively correlated with effective porosity, while the proportion of small and medium-sized pores is positively correlated with effective porosity. The effective porosity is significantly linearly related to coal permeability, indicating that the pore size distribution of coal affects the effective porosity of coal, thereby affecting the permeability of coal; The effective porosity directly affects the permeability of coal seams and is also related to coal quality parameters, which can be used as one of the indicators to evaluate the properties of coal seams to a certain extent .
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图 1 煤层空间位置关系示意
Figure 1. Schematic diagram of spatial position relationship of coal seams
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图 4 扫描电镜下煤中微孔裂隙特征
Figure 4. Characteristics of microporous cracks in coal under scanning electron microscopy
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图 9 饱水−离心联测有效孔隙率曲线
Figure 9. Effective porosity curves of saturation centrifuge combined measurement
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图 10 有效孔隙率随孔径占比关系曲线
Figure 10. Curve of effective porosity as a function of pore size proportion
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图 12 有效孔隙率与煤质参数关系曲线
Figure 12. Relationship curve of effective porosity with coal quality parameters
表 1 试验煤样工业分析
Table 1 Proximate analysis data of experimental coal samples
煤样 Mad/% Aad/% Vdaf/% FCad/% 6号硬煤−1 1.33 5.85 35.90 35.90 6号硬煤−2 1.24 5.56 32.95 36.38 6号硬煤−3 1.24 5.56 32.95 36.38 6号软煤−1 1.58 13.14 31.52 31.52 6号软煤−2 1.43 18.15 28.75 32.73 8号硬煤−1 1.14 6.04 38.02 38.02 8号硬煤−2 1.08 7.34 36.98 38.88 8号硬煤−3 0.92 6.92 38.67 39.42 8号软煤−1 1.39 39.76 23.93 23.93 8号软煤−2 1.34 38.66 20.14 19.54 
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表 2 煤层孔裂隙类型及成因
Table 2 Types and genesis of coal seam pore fractures
煤层 发育孔裂隙类型 成因简述 连通性 6号煤 碎粒孔
摩擦孔受构造应力破坏形成碎粒间孔隙
受构造应力破坏形成碎粒间孔隙差
差气孔
溶蚀孔矿物质在水、汽作用下溶蚀形成
受压应力作用面与面摩擦形成一般
差张性裂隙
剪性裂隙受张应力作用产生
受剪应力作用产生好
好8号煤 角砾孔
气孔
铸模孔受构造应力破坏形成角砾间孔隙
成煤过程中生气、聚气作用形成
矿物质因硬度差异形成印坑好
一般
差张性裂隙
剪性裂隙受张应力作用产生
受剪应力作用产生好
好
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表 3 各类孔径尺寸对应比例
Table 3 Corresponding proportions of various aperture sizes
煤样 孔径区间占比/% 微孔（0～0.01 μm ） 小孔（>0.01～0.10 μm） 中孔（>0.1～1.0 μm） 大孔（>1 μm） Y−6−1 55.6585 10.6522 5.4142 28.2765 Y−6−2 49.0186 13.8105 7.5423 29.6287 Y−8−1 48.2199 10.4826 11.8853 29.4122
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表 4 基于NMR-T2C法煤样孔隙率及渗透率
Table 4 Porosity and permeability of coal samples based on NMR T2C method
煤样 核磁
孔隙率φ/%可动流体
孔隙率φF/%束缚流体
孔隙率φB/%T2
截止值/ms自由流体
饱和度IFF/%束缚流体
饱和度IBV/%核磁渗透率
K/10−3μm 2Y−6−1 1.60 0.57 1.03 0.77 35.81 64.19 0.013 Y−6−2 1.45 0.63 0.82 0.70 43.73 56.27 0.016 Y−8−1 1.51 0.74 0.77 0.55 49.05 50.95 0.030
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