安全与环境学报

为探究酸化作用下煤体孔隙结构及分形维数的演化特征，基于低场核磁共振技术及分形维数理论，在开展不同酸化时间条件下高阶煤T₂谱测试的基础上，深入分析了酸化作用下高阶煤的T₂谱形态、孔径分布、孔隙度、分形维数等参数的演化特征，同时研究了酸化作用下煤体孔隙结构复杂性的演化规律，并分析了酸化作用下煤体的渗流孔分形维数与孔隙度的相关性，建立了煤体孔隙复杂程度与孔隙连通性的联系。结果表明：经酸化处理后，煤体全孔径孔隙数量及孔体积皆显著增大，增幅呈现中孔最大、大孔次之、小孔较小、微孔负增长的状态；煤中全孔径尺度、孔隙数量、孔体积均随酸化时间的延长逐渐增大，酸化初期各孔体积增幅最为显著，酸化6 h时渗流孔体积急剧增大，增幅高达205.85%，随着酸化时间的继续延长，各孔体积的增幅逐渐变缓，酸化18 h、24 h、36 h时吸附孔和渗流孔体积均保持基本不变，微小孔占比逐渐降低，中大孔占比逐渐增大，中大孔体积占比较酸化前增加了10.63百分点，酸化作用对微小孔与中孔之间的连通性改善效果较差，对中孔与大孔之间的连通性改善效果较好；不同酸化时间下煤样的渗流孔皆具有明显的分形特征，渗流孔分形维数随酸化时长的增加逐渐降低，渗流孔隙的非均质性、复杂程度逐渐降低，孔隙间的连通性逐渐增强；孔隙度与渗流孔分形维数之间呈线性负相关，线性斜率为-135.48。

In order to explore the evolutionary characteristics of pore structure and fractal dimension of coal under acidification， the maceral analysis， industrial analysis， and vitrinite reflectance tests of coal samples were first conducted. Subsequently， based on low-field Nuclear Magnetic Resonance (NMR) technology and fractal dimension theory， T₂ spectrum tests of high-rank coal under different cumulative acidification time conditions were performed， and the fractal dimensions of adsorption pores and seepage pores in the coal samples were calculated. The evolution characteristics of T₂ spectrum morphology， pore size distribution， porosity， fractal dimension， and other parameters of high-rank coal under acidification were analyzed in depth. By examining the fractal dimension of seepage pores， the complexity evolution law of coal pore structure under acidification was studied. The correlation between the fractal dimension of seepage pores and the porosity of coal under acidification was analyzed， and the relationship between pore complexity and pore connectivity of coal was established. The results indicate that after acidification treatment， both the number and volume of pores across the entire pore diameter of the coal body increase significantly， with the highest increase observed in medium pores， followed by large pores. The increase for small pores is less pronounced， while micro pores exhibit a negative growth. As the acidification time increases， the overall pore size scale， pore number， and pore volume in the coal gradually rise. The volume of each pore increases most significantly at the initial stage of acidification. At 6 hours of acidification， the volume of seepage pores sharply increases， showing an increase of up to 205.85%. As the acidification time continues to rise， the rate of volume increase for each pore gradually slows down. The volumes of adsorption pores and seepage pores remain basically unchanged at 18 h， 24 h， and 36 h of acidification. The proportion of micro-small pores gradually decreases， while the proportion of medium-large pores increases， rising from 1.88% before acidification to 12.51% after 72 h of acidification. After 72 h of acidification， the volume of mesopores and macropores increased by 10.63 percentage points compared to before acidification. Acidification had a limited effect on improving the connectivity between micropores and mesopores， while it effectively improved the connectivity between mesopores and macropores. The nuclear magnetic porosity and its increase in coal gradually rise with increasing acidification time; the longer the acidification time， the greater the increase in porosity. The seepage pores of coal samples under different acidification times exhibit distinct fractal characteristics. The fractal dimension of seepage pores gradually decreases with increasing acidification time， indicating a reduction in heterogeneity and complexity， as well as an increase in pore connectivity. A linear negative correlation exists between porosity and the fractal dimension of seepage pores， with a linear slope of -135.48.