Characterization of coal micro-structure and the associated rock mechanical properties are of key importance for coal seam exploration, coal bed methane development, enhanced coal bed methane production and CO₂ storage in deep coal seams. Considerable knowledge exists about coal chemical properties, but less is known about the nanoscale to the micro-scale structure of coals and how they change with coal strength across coal ranks. Thus, in this study, 3D X-ray micro-computed tomography (with a voxel size of 3.43 µm) and nano-indentation tests were conducted on coal samples of different ranks from peat to anthracite. The micro-structure of peats showed a well-developed pore system with meso- and micro-pores. The meso-pores essentially disappear with increasing rank, whereas the micro-pores persist and then increase past the bituminous rank. The micro-fracture system develops past the peat stage and by sub-bituminous ranks and changes into larger and mature fracture systems at higher ranks. The nano-indentation modulus showed the increasing trend from low- to high-rank coal with a perfect linear relationship with vitrinite reflectance and is highly correlated with carbon content as expected.

中文翻译：

---

不同等级煤的纳米力学性质和孔隙特征

煤的微观结构及其相关的岩石力学特性的表征对于煤层勘探，煤层气开发，提高煤层气产量和CO ₂至关重要。储存在深层煤层中。关于煤化学性质的知识很多，但对煤的纳米级到微观结构以及它们如何随着煤等级的变化而变化的了解却很少。因此，在这项研究中，对从泥炭到无烟煤的不同等级的煤样品进行了3D X射线微计算机断层扫描（体素尺寸为3.43 µm）和纳米压痕测试。泥炭的微观结构显示出发达的孔隙系统，具有中孔和微孔。中孔基本上随着等级的增加而消失，而微孔持续存在，然后增加到超过沥青等级。微裂缝系统发展到泥炭阶段之后，并发展到次沥青阶次，并在更高阶次转变成更大而成熟的裂缝系统。