NMR serves as an important technique for probing rock pore space, such as pore structure characterization, fluid identification, and petrophysical property testing, due to the reusability of cores, convenience in sample processing, and time efficiency in laboratory tests. In practice, NMR signal collection is normally achieved through polarized nuclei relaxation which releases crucial relaxation messages for result interpretation. The impetus of this work is to help engineers and researchers with petroleum background obtain new insights into NMR principals and extend existing methodologies for characterization of unconventional formations. This article first gives a brief description of the development history of relaxation theories and models for porous media. Then, the widely used NMR techniques for characterizing petrophysical properties and pore structures are presented. Meanwhile, limitations and deficiencies of them are summarized. Finally, future work on improving these insufficiencies and approaches of enhancement applicability for NMR technologies are discussed.

中文翻译：

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低场核磁共振（NMR）技术在岩石内部孔隙空间表征中的应用进展

由于岩心的可重用性，样品处理的便利性以及实验室测试的时间效率，NMR是探测岩石孔隙空间的重要技术，例如孔隙结构表征，流体识别和岩石物性测试。在实践中，通常通过极化核弛豫实现NMR信号收集，极化核弛豫释放出关键的弛豫信息用于结果解释。这项工作的推动力是帮助具有石油背景的工程师和研究人员获得对NMR原理的新见解，并扩展用于表征非常规地层的现有方法。本文首先简要介绍了多孔介质松弛理论和模型的发展历史。然后，介绍了表征岩石物性和孔隙结构的广泛使用的NMR技术。同时，总结了它们的局限性和不足。最后，讨论了改善这些不足的未来工作以及增强NMR技术适用性的方法。