Abstract With a focus on different CO2 pressures and H2O, the influences of the ScCO2–H2O coupling effect on the microstructures of low-rank coal samples were compared and analyzed, offering further analysis of the CO2 sequestration capacity in coal seams rendered unworkable owing to the effect of water. By using nuclear magnetic resonance (NMR) and X-ray powder diffraction (XRD), the changes in porosity, pore size, pore size distribution (PSD), fractal dimension, and minerals in coal samples of the two states were compared and analyzed. XRD analysis revealed that a large number of carbonate rocks (calcite) and aluminosilicate minerals (clay minerals) were found in coal. ScCO2 presented the optimal dissolution effect in the water-saturated samples. NMR analysis showed that compared with a single CO2 fluid, the pore structures of the coal samples varied more remarkably under the coupling effect of CO2 and H2O. Moreover, under the supercritical state of CO2, the effect on the coal sample was the greatest. With the increase in pressure during the CO2 treatment, the porosity of the coal samples increased, and the proportion of macropores grew, indicating the transformation of small pores into large pores. The roughness of adsorption pores increased, whereas the complexity and heterogeneity of seepage pores in the coal samples after ScCO2 treatment declined. Generally, the ScCO2–H2O coupling effect on coal samples caused further changes in the pore structures, promoting mineral dissolution in the coal samples.

中文翻译：

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超临界CO2和水处理后低阶煤微观结构的变化

摘要 针对不同的 CO2 压力和 H2O，对比分析了 ScCO2-H2O 耦合效应对低阶煤样品微观结构的影响，进一步分析了煤层因水的作用。通过核磁共振(NMR)和X射线粉末衍射(XRD)对两种状态煤样的孔隙率、孔径、孔径分布(PSD)、分形维数和矿物的变化进行比较分析。XRD分析表明，煤中发现了大量碳酸盐岩（方解石）和铝硅酸盐矿物（粘土矿物）。ScCO2 在水饱和样品中表现出最佳溶解效果。核磁共振分析表明，与单一的 CO2 流体相比，在CO2和H2O的耦合作用下，煤样的孔隙结构变化更为显着。而且，在CO2超临界状态下，对煤样的影响最大。随着CO2处理压力的增加，煤样孔隙度增大，大孔比例增大，表明小孔向大孔转变。ScCO2处理后煤样中吸附孔的粗糙度增加，而渗流孔的复杂性和非均质性下降。一般而言，ScCO2-H2O 对煤样的耦合作用会引起孔隙结构的进一步变化，促进煤样中的矿物溶解。对煤样的影响最大。随着CO2处理压力的增加，煤样孔隙度增大，大孔比例增大，表明小孔向大孔转变。ScCO2处理后煤样中吸附孔的粗糙度增加，而渗流孔的复杂性和非均质性下降。一般而言，ScCO2-H2O 对煤样的耦合作用会引起孔隙结构的进一步变化，促进煤样中的矿物溶解。对煤样的影响最大。随着CO2处理压力的增加，煤样孔隙度增大，大孔比例增大，表明小孔向大孔转变。ScCO2处理后煤样中吸附孔的粗糙度增加，而渗流孔的复杂性和非均质性下降。一般而言，ScCO2-H2O 对煤样的耦合作用会引起孔隙结构的进一步变化，促进煤样中的矿物溶解。而ScCO2处理后煤样渗流孔的复杂性和非均质性下降。一般而言，ScCO2-H2O 对煤样的耦合作用会引起孔隙结构的进一步变化，促进煤样中的矿物溶解。而ScCO2处理后煤样渗流孔的复杂性和非均质性下降。一般而言，ScCO2-H2O 对煤样的耦合作用会引起孔隙结构的进一步变化，促进煤样中的矿物溶解。