西山煤田不同变质程度煤孔隙结构分形特征及影响因素研究

为研究煤的多孔介质属性及其分形特征,以山西沁水盆地西山煤田为研究对象,采用扫描电镜(SEM)分析了煤表面孔隙结构特征。基于SEM图片,通过盒维数法计算得到了不同煤样表面孔隙分形维数,并分析了其影响因素。研究结果表明:煤表面具有显著的分形特征,分形理论能够较好地描述煤孔隙结构复杂程度;在本测试煤样中,不同煤样分形维数值在1.33～1.92范围内变化;变质程度、水分、埋深、坚固性系数(f值)对煤孔隙分形维数有显著影响,随Ro和埋深的增加煤体表面孔隙趋于复杂化,分形维数值不断增大;而水分和灰分的存在使得煤体表面变得相对光滑,能够减小分形维数值。分形维数是衡量煤孔隙复杂程度的有效参数,在煤矿现场瓦斯防治中,对于具有高分形维数的煤体,应该引起重视。这类煤体往往破坏程度较高,具有强吸附性,孔隙连通性差,瓦斯抽采困难,在煤炭开采过程中,容易导致煤与瓦斯突出、瓦斯涌出等灾害。

Study on the fractal feature of coal pore structure with different ranks and its influencing factors in Xishan coal field

In order to investigate the porous medium property of coal, Xishan coalfield in Qinshui Basin, Shanxi Province was taken as the study object. The scanning electron microscopy (SEM) was adopted to analyze the pore strcutue characteristics on coal surface. Based on the SEM images, the pore fractal dimension of various coal samples was obtained through the box-counting method. Meanwhile, the influencing factors of fractal dimension was also analyzed. The research results indicate that coal surafe has the obvious fractal feature, and the complexity of coal pore structure can be well descibed by fractal theory. The value of fractal dimension ranges from 1.33 to 1.92 for different coal samples. Coalification, water content, burial depth and Protodyakonov"s coefficient (f value) have significant impact on fractal dimension of coal pore. As the Ro increase of and burial depth, coal surface tends to be rough and complex, leading to the increase of fractal dimension. However, the existence of water and ash content enables the coal surface to become relatively smooth, consequently, the value of fractal dimension is reduced.