The confinement effect in nanopores significantly impacts the phase behavior of fluids in unconventional reservoirs and controls the occurrence and transport of fluids. As a result, the phase behavior, thermodynamic properties and phase equilibrium of bulk gases, in particular, could significantly change due to the surface-molecules interactions. On the one hand, due to the heterogeneous and anisotropic nature of unconventional reservoirs, experimental analysis of the confinement effects is utterly challenging. On the other hand, molecular simulation techniques for characterizing confinement effects are inaccurate since most of them are not verified with experimental data. In this work, we have reviewed the experimental results in the literature focusing on the confinement effect in nanopores. The behavior of confined gases in shale and coal reservoirs can be obtained by analyzing the small-angle neutron/X-ray scattering (SANS/SAXS) data using in-situ measurement and contrast matching small-angle neutron scattering (CM-SANS) methodologies. We reviewed the phase transition of confined carbon dioxide and methane in nanopores where the densities of both would differ from their bulk densities and are known to be pressure- or pore-size-sensitive. The current work investigates the application and future perspectives of utilizing the confinement effect in shale and coal reservoirs for enhancing gas/oil recovery and carbon dioxide sequestration. Additionally, given the recent global interest in hydrogen storage in such reservoirs, our literature review concludes that shale and coal reservoirs might be considered as repositories for hydrogen if the confinement effect of fluids is well understood.

中文翻译：

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页岩和煤储层纳米孔隙的限域效应：实验表征方法综述

纳米孔的限域效应显着影响非常规油藏流体的相行为，控制流体的赋存和运移。因此，特别是大宗气体的相行为、热力学性质和相平衡可能由于表面分子相互作用而发生显着变化。一方面，由于非常规油藏的非均质性和各向异性，限制效应的实验分析极具挑战性。另一方面，用于表征限制效应的分子模拟技术是不准确的，因为大多数技术都没有得到实验数据的验证。在这项工作中，我们回顾了文献中关注纳米孔限域效应的实验结果。页岩和煤储层中受限气体的行为可以通过使用原位测量和对比匹配小角中子散射 (CM-SANS) 方法分析小角中子/X 射线散射 (SANS/SAXS) 数据来获得。我们回顾了纳米孔中受限二氧化碳和甲烷的相变，其中两者的密度与其体积密度不同，并且已知对压力或孔径敏感。目前的工作研究了利用页岩和煤储层的限制效应来提高天然气/石油采收率和二氧化碳封存的应用和未来前景。此外，鉴于最近全球对此类储层储氢的兴趣，我们的文献综述得出的结论是，如果充分理解流体的限制效应，页岩和煤储层可能被视为氢气储存库。