Abstract Understanding the mechanical response of coal to CO2 injection is necessary to determine the suitability of a seam for carbon capture and underground storage (CCUS). The bulk elastic properties of a coal or shale, which determine its mechanical response, are controlled by the elastic properties of its individual components, i.e. macerals and minerals. The elastic properties of minerals are relatively well understood, and attempts have been made previously to acquire maceral elastic properties (Young's modulus) by means of nanoindentation. However, due to the resolution of a nanoindent and small size of macerals; the response is likely to be from a combination of macerals composition and spatial distribution. Here atomic force microscopy is used for the first time to give a unique understanding of the local Youngs modulus of individual macerals, with a precision of 10 nm in both immature and mature coals/shale. Alginite, cutinite, inertinite and sporinite macerals are analysed from a samples of cannel coal(rich in cutinite), paper coal (enriched in sporinite), Northumberland coal (higher rank coal, rich in vitrinite and inertinite) and alginite rich New Albany Shale. Initial findings on the New Albany Shale indicate that kerogen isolation is not a suitable preparation technique for atomic force microscopy and as such, no alginite maceral moduli are reported. Therefore only results of the coal derived macerals (cutinite, inertinite and sporinite) are included in this study. The results at this length scale indicate that the mean and modal Youngs modulus values in all coal macerals is less than 10GPa. This range is similar to Young's modulus values acquired by nanoindentation within previous studies. A major difference is that the modal modulus values obtained here are significantly lower than the modal values obtained within previous studies. Thermally immature liptinite macerals (cutinite/sporinite) have a lower modal modulus(1.35–2.97GPa) than the inertinites (1.44–3.42GPa) from the same coal. The modulus response is also non-normally distributed and most likely conform to a gamma distribution with shape parameter between 1.5 and 2.5. The modal Youngs modulus of all macerals increases with maturity, but not at the same rate, whereby the liptinite macerals become stiffer than the inertinites by the dry gas window (1.56 % Ro in Northumberland Coal). Modelling of volumetric strain under CO2 injection indicates an inversely proportionate relationship to Youngs modulus, which suggest that differential swelling is more likely to occur in immature coals. It is therefore preferable to target mature coals for CCUS, as the reaction of macerals at higher maturities is more predictable across an entire coal seam.

中文翻译：

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煤质的地质力学性质；适用于模拟 CO2 封存过程中煤层膨胀的测量

摘要 了解煤对 CO2 注入的机械响应对于确定煤层对碳捕获和地下储存 (CCUS) 的适用性是必要的。煤或页岩的整体弹性特性决定了它的机械响应，它受其各个组分（即矿物和矿物）的弹性特性控制。矿物的弹性特性相对较好地理解，并且先前已经尝试通过纳米压痕获得宏观弹性特性（杨氏模量）。然而，由于纳米压痕的分辨率和微晶的小尺寸；反应很可能来自于材料成分和空间分布的组合。在这里，原子力显微镜首次用于对单个微晶的局部杨氏模量提供独特的理解，在未成熟和成熟煤/页岩中的精度均为 10 nm。从罐煤（富含角质素）、纸煤（富含孢子石）、诺森伯兰煤（更高级的煤，富含镜质体和惰性）和富含褐藻石的新奥尔巴尼页岩样品中分析了褐藻石、角质石、惰性和孢子石微晶。新奥尔巴尼页岩的初步发现表明，干酪根分离不是原子力显微镜的合适制备技术，因此，没有报告褐藻岩微晶模量。因此，本研究仅包括煤衍生的微晶（角质质、惰性和孢子质）的结果。该长度尺度的结果表明，所有煤质的平均和模态杨氏模量值都小于 10GPa。该范围类似于以前研究中通过纳米压痕获得的杨氏模量值。一个主要区别是此处获得的模态模量值明显低于先前研究中获得的模态值。热不成熟的 liptinite maerals (cutinite/sporinite) 的模态模量 (1.35–2.97GPa) 比来自相同煤的惰性 (1.44–3.42GPa) 低。模量响应也是非正态分布的，很可能符合形状参数在 1.5 和 2.5 之间的伽马分布。所有微晶的模态杨氏模量随着成熟度的增加而增加，但速度不同，通过干气窗口（Northumberland Coal 中的 Ro 为 1.56 %），liptinite macerals 变得比惰性物质更硬。CO2 注入下的体积应变建模表明与杨氏模量成反比关系，这表明在未成熟煤中更可能发生差异膨胀。因此，CCUS 的目标是成熟煤，因为在整个煤层中，更高成熟度的煤体反应更可预测。