Geomechanical properties of coal macerals; measurements applicable to modelling swelling of coal seams during CO2 sequestration
Geomechanical properties of coal macerals; measurements applicable to modelling swelling of coal seams during CO2 sequestration
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DOI：
10.1016/j.coal.2020.103528
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发表时间：
2020-06
影响因子：
5.6
通讯作者：
T. Fender;M. Rouainia;C. Land;D. Jones;M. Mastalerz;Jan A.I. Hennisen-;S. Graham;T. Wagner
中科院分区：
文献类型：
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作者：
T. Fender;M. Rouainia;C. Land;D. Jones;M. Mastalerz;Jan A.I. Hennisen-;S. Graham;T. Wagner
了解煤对CO2注入的机械响应对于确定煤层的碳捕获和地下储存（CCUS）的适用性是必要的。煤或页岩的体积弹性性质决定其机械响应，其由其单个组分（即显微组分和矿物）的弹性性质控制。矿物的弹性性质是相对较好地理解的，并且先前已经尝试通过纳米压痕来获得显微组分弹性性质（杨氏模量）。然而，由于显微组分的纳米级分辨率和小尺寸，响应可能来自显微组分组成和矿物的组合。在这里，原子力显微镜是第一次使用，以提供一个独特的理解个别显微组分的本地杨氏模量，在未成熟和成熟的煤/页岩的精度为10纳米。对烛煤（富含角质体）、纸煤（富含孢子体）、诺森伯兰煤（高煤阶煤，富含镜质组和惰质组）和富含藻体的新奥尔巴尼页岩样品中的藻体、角质体、惰质组和孢子体显微组分进行了分析。对新奥尔巴尼页岩的初步研究结果表明，干酪根分离不是原子力显微镜的合适制备技术，因此，没有准确报道藻岩显微组分模量。因此，煤岩显微组分（角质体，惰质体和孢子体）的结果包括在本研究中。结果表明，在这个长度尺度上，所有煤显微组分的平均和模态杨氏模量值小于10 GPa。这个范围是类似的杨氏模量值在以前的研究中获得的纳米压痕。一个主要的区别是，这里获得的模态模量值显着低于在以前的研究中获得的模态值。热未成熟的镜质组显微组分（角质体/孢子体）的模态模量（1.35-2.97GPa）低于同一煤的惰质组（1.44- 3.42GPa）。模量响应也是非正态分布的，并且很可能符合形状参数在1.5和2.5之间的伽马分布。所有显微组分的模态杨氏模量随成熟度增加，但不是以相同的速率增加，由此，在干气窗口（1.56% Roin Northumberland煤），脂质体显微组分变得比惰性组分更硬。CO2注入下的体积应变模型表示成反比的关系，杨氏模量，这表明，差异溶胀更有可能发生在未成熟的煤。因此，CCUS优选以成熟煤为目标，因为在整个煤层中，更高成熟度的显微组分的反应更可预测。
Understanding the mechanical response of coal to CO2injection 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 minerals. 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 accurately reported. Therefore 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 Young's modulus values in all coal macerals is less than 10 GPa. 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 (1.44–3.42 GPa) from the same coal. The modulus response is also non-normally distributed and most likely conforms to a gamma distribution with shape parameter between 1.5 and 2.5. The modal Young's 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 % Roin Northumberland Coal). Modelling of volumetric strain under CO2injection indicates an inversely proportionate relationship to Young's modulus, which suggests 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.