College of Geological and Surveying Engineering, Taiyuan University of Technology
Xi’an Research Institute (Group) Company Limited, China Coal Technology and Engineering Group Corporation
School of Safety Science and Engineering, Xi’an University of Science and Technology
College of Mining Engineering, Taiyuan University of Technology

深部CO2封存技术(CO2-ECBM技术)具有提高煤层气产量和封存CO2的双重作用,但超临界二氧化碳(ScCO2)与煤相互作用会导致煤结构发生改变进而影响其吸附能力,而Sc-CO2作用后煤结构的变化及对储层的影响目前尚不明确。以山西晋城成庄煤矿二叠系山西组三号煤层为研究对象,在高压注入CO2吸附实验的基础上,采用原子力显微镜(AFM)和傅立叶变换红外光谱(FTIR)技术,分析ScCO2对样品纳米孔隙结构、官能团与芳香结构的影响。使用Mate-rialsStudio2019软件构建煤超分子结构模型,运用ReaxFF-MD模拟煤分子结构的反应途径、转化路径和动力学行为。将实验与分子模拟相结合,从纳米-分子尺度分析ScCO2作用后煤中孔隙结构与化学结构的变化机理及耦合关系。结果表明:ScCO2作用后,孔隙排列无序性增加,微孔体积增加26.7%,比表面积增加2.81%,平均孔径由1.16nm增加到1.31nm;3D平均粗糙度Ra由1.43变为1.57,3D均方根粗糙度Rq由2.34变为2.65,峰度系数Rku由2.78变为2.56,表面偏斜度Rsk由-0.64变为-0.87。反应过程中样品化学结构变化经历四个阶段:结构增大、边缘支链断裂、芳香结构移位和芳香结构复位。脂肪结构含量增加,芳香结构含量减少,Cal—Cal数量由61增加到72又减少到63,Car—Car数量由176减少到154又增加到162,C—H数量由146减少到122,C—O数量由29减少到14。ScCO2作用下煤孔隙结构随化学结构变化的关系为:低能键断裂形成新孔但数量有限,芳香结构膨胀导致孔径变小,长链结构占据原有孔隙空间,使分子间孔转化为分子内孔,芳香结构的开环和重组则显著增大孔隙。

Deep CO sequestration technology (CO -ECBM) has the dual function of en- hancing coalbed methane production and storing CO . However, the interaction between super- critical carbon dioxide (ScCO ) and coal can lead to structural changes in coal, thereby affecting its adsorption capacity. The specific changes in coal structure and their impact on reservoirs after ScCO treatment remain unclear. This study focuses on the Permian Shanxi Formation No.3 coal seam in the Chengzhuang mine, Jincheng, Shanxi. Based on high-pressure CO injection adsorp- tion experiments, atomic force microscopy (AFM) and Fourier-transform infrared spectroscopy (FTIR) techniques are used to analyze the effects of ScCO on the sample’s nanoscale pore struc- ture, functional groups, and aromatic structures. Additionally, the Materials Studio soft- ware is used to establish pore structure models of coal, and ReaxFF-MD is employed to simulate the reaction pathways, transformation routes, and kinetic behaviors of coal molecular structures. By combining experimental data with molecular simulations, the variation mechanisms and cou- pling relationship of pore structures and chemical structures in coal after ScCO treatment were analyzed, from the nano-to molecular-scale. The results show that after exposure to ScCO , the pore disorder increases, with a 26.7% increase in micropore volume, a 2.81% increase in specific surface area, and an average pore diameter increase from 1.16 nm to 1.31 nm. 3D average rough- ness R increases from 1.43 to 1.57, and 3D root-mean-square roughness R rises from 2.34 to 2.65, while kurtosis coefficient R decreases from 2.78 to 2.56, and surface skewness R chan- ges from -0.64 to -0.87. During the reaction process, the chemical structure of the sample un- dergoes four stages of change: structural expansion, breaking of peripheral side chains, displace- ment of aromatic structures, and recovery of aromatic structures. The content of aliphatic struc- tures increases, while the content of aromatic structures decreases. The number of C —C bonds initially increases from to and then decreases to 63; the number of C —C bonds decreases from to and then increases to 162; the number of C—H bonds decreases from to 122; and the number of C—O bonds decreases from to 14. Under the influence of ScCO , the rela- tionship between the chemical structure changes and pore structure in coal evolves as follows: breaking of low-energy bonds forms new pores, though in the limited quantities; the expansion of aromatic structures leads to a reduction in pore diameter; long-chain structures occupy the origi- nal pore spaces, converting inter-molecular pores into intra-molecular pores; and the opening and recombination of aromatic rings significantly increase the pore size.

国家自然科学基金项目(42103047)和山西省基础研究计划项目(20210302124644).

董 夔,贾秉义,孔少奇,等.ScCO2 作用 下 晋 城 成 庄 无 烟 煤 结 构 变 化 及 机 理 研 究[J].煤 炭 转 化,2024,47(6):1-14

DONG Kui,JIA Bingyi,KONG Shaoqi,et al.Study on structural changes of Jincheng Chengzhuang anthracite under treatment of ScCO2 and its mechanisms[J].Coal Conversion,2024,47(6):1-14