CO₂ sequestration in deep unminable coal seams is currently identified as a research hot spot to reduce CO₂ emissions, due to the potential large-scale storage capacity and complicated physical and chemical reactions, especially for supercritical CO₂ (scCO₂). Hitherto, the interaction mechanisms between scCO₂ and coal mass in situ conditions are still unclear. Therefore, the main objective of this study is to fully address the coupling effects of scCO₂ sequestration on coal mass and provide a comprehensive evaluation of the interrelation of these variations. Five cycles of helium and scCO₂ injection were replicated on a subbituminous coal sample to investigate the permeability variation with scCO₂ saturation time. Meanwhile, gas chromatography–mass spectrometry (GC–MS), gas chromatography (GC), Fourier transform infrared spectroscopy (FTIR), proximate analysis, and low-pressure–temperature nitrogen (N₂) isotherm analyses were employed to characterize the transformation in coal mass. The test result shows the following: (1) scCO₂ tended to mobilize a higher proportion of aliphatics than aromatics, and the concentration of the yielded hydrocarbons decreased with CO₂ saturation time. (2) Carbonate and silicate cemented minerals were partly dissolved due to the formation of an acidic solution containing H₂CO₃. (3) The hydrocarbon extraction and mineral dissolution resulted in the corresponding FTIR absorbance bands being weakened and the volatile matter content and the ash content being decreased by approximately 15 and 26%, respectively. (4) The coal pore volume and the Brunauer–Emmett–Teller (BET) surface area decreased by approximately 24 and 12%, respectively. (5) Due to CO₂ adsorption and the reduction of Young’s modulus with saturation time, the volumetric strain increased from 0.23 to 3.26%, which led to coal permeability decrease from 0.042 to 0.029 mdarcy. After analysis of the interrelation of these variations, the interaction mechanisms between scCO₂ and coal mass in situ conditions were described and an overall negative effect on coal permeability was found.

中文翻译：

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煤层超临界CO ₂固存的耦合效应

由于潜在的大规模存储容量以及复杂的物理和化学反应，特别是对于超临界CO ₂（scCO ₂），深层不可开采煤层中的CO ₂固存目前被确定为减少CO ₂排放的研究热点。迄今为止，scCO ₂与煤质原位条件之间的相互作用机理仍不清楚。因此，本研究的主要目的是充分解决scCO ₂螯合对煤质的耦合作用，并对这些变化之间的相互关系提供全面的评估。氦气和scCO _2的五个循环在次烟煤样品上重复注入，以研究渗透率随scCO ₂饱和时间的变化。同时，采用气相色谱-质谱（GC-MS），气相色谱（GC），傅立叶变换红外光谱（FTIR），近距离分析和低压-氮气氮（N ₂）等温线分析来表征煤块。试验结果表明：（1）scCO ₂倾向于比芳香族迁移更多的脂族脂肪，并且随着CO ₂饱和时间的增加，生成的碳氢化合物的浓度降低。（2）由于形成了含有H ₂的酸性溶液，碳酸盐和硅酸盐胶结的矿物被部分溶解。CO ₃。（3）碳氢化合物提取和矿物溶解导致相应的FTIR吸收带减弱，挥发性物质含量和灰分含量分别降低了约15％和26％。（4）煤的孔隙体积和Brunauer-Emmett-Teller（BET）表面积分别减少了约24％和12％。（5）由于CO _2的吸附和杨氏模量随饱和时间的降低，体积应变从0.23增加到3.26％，导致煤的渗透率从0.042降低到0.029。在分析了这些变异的相互关系之后，scCO ₂之间的相互作用机制 描述了煤的原位条件，发现了对煤渗透性的整体负面影响。