The porous structure of geomaterials is of utmost importance for various industrial and natural processes. In this study, various conventional porous structure characterization techniques such as mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), micro-X-ray computed tomography (μCT) imaging, as well as gas injection have been employed to perform a systematic and critical evaluation of all such techniques for characterization of a carbonate rock sample porous structure. The porosity obtained from μCT (5 μm/voxel) (21.5%) is closer than the overall porosity obtained by MIP (17.23%) to the gas porosimetry result (23%). The 5% difference could be due to inaccessible pores to mercury, which can be accessible to nitrogen with much smaller molecules. The porosity obtained from NMR is 21.4%. It is lower than porosity values by μCT (5 μm/voxel) and by gas injection and higher than the prediction of MIP. The porosity is obtained by μCT, but the much lower resolution (27.5 μm/voxel) results in 8.19% underestimating the porosity by around 50%. Regarding permeability, the results of the NMR technique are highly dependent on the cutoff range used and very different from other techniques, whereas the permeability obtained by MIP is around 18.42 mD, close to that obtained by gas permeameter (20 mD). The μCT imaging provides the opportunity to measure pore and throat size distribution directly, to achieve open and closed porosity, the coordination number of pores and surface and volume characteristics of the porous medium, which can hardly be performed through other techniques. The resolution of images, however, fully controls the obtained pore and throat size distribution in CT analysis. The Kolmogorov–Smirnov distribution analysis reveals that the resulting pore size distribution from MIP is rather a rough estimation of the throat size distribution obtained from μCT (5 μm/voxel), while NMR prediction can provide a rather good approximation of the pore size distribution obtained from μCT (5 μm/voxel). The NMR prediction is however dependent on the choice made for the surface relaxivity coefficient, and changing it would significantly affect the resulting distribution. The results of this study provide further insight and elucidate the differences of the quantities such as porosity, permeability, and pore and throat size distribution obtained from various techniques which are essential either as an input to numerical models of flow and transport in porous media or as a building block of the theoretical models.

中文翻译：

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岩石多孔结构表征：对各种最先进技术的批判性评估

土工材料的多孔结构对于各种工业和自然过程至关重要。在这项研究中，各种传统的多孔结构表征技术，如压汞法 (MIP)、核磁共振 (NMR)、显微 X 射线计算机断层扫描 (μCT) 成像以及气体注入已被用于执行系统的以及对用于表征碳酸盐岩样品多孔结构的所有此类技术的批判性评估。从 μCT (5 μm/voxel) 获得的孔隙率 (21.5%) 比通过 MIP 获得的总体孔隙率 (17.23%) 更接近于气体孔隙率测量结果 (23%)。5% 的差异可能是由于无法进入汞的孔隙，而具有更小分子的氮可以进入。从NMR获得的孔隙率为21.4%。它低于μCT（5μm/体素）和注气的孔隙度值，高于MIP的预测。孔隙率是通过 μCT 获得的，但分辨率低得多（27.5 μm/体素）导致 8.19% 的人低估了孔隙率约 50%。关于渗透率，核磁共振技术的结果高度依赖于所使用的截止范围，与其他技术非常不同，而 MIP 获得的渗透率约为 18.42 mD，接近气体渗透计 (20 mD) 获得的渗透率。μCT成像提供了直接测量孔喉尺寸分布的机会，实现了其他技术难以实现的开闭孔隙度、孔隙配位数以及多孔介质的表面和体积特征。然而，图像的分辨率，完全控制 CT 分析中获得的孔喉尺寸分布。Kolmogorov-Smirnov 分布分析表明，MIP 得到的孔径分布是对从 μCT (5 μm/体素) 获得的喉道尺寸分布的粗略估计，而 NMR 预测可以提供获得的孔径分布的相当好的近似值来自 μCT（5 μm/体素）。然而，NMR 预测取决于表面弛豫系数的选择，改变它会显着影响结果分布。这项研究的结果提供了进一步的见解并阐明了孔隙度、渗透率、