NMR T₂ relaxation times for fluids in a porous medium are, in principle, proportional to the relevant occupied pore size. Here, we exploit this relationship to monitor the pore size distribution occupied by methane (CH₄) at 100 bar and room temperature in both sandstone and carbonate rock cores, while it is displaced by a range of miscible fluids: carbon dioxide (CO₂), nitrogen (N₂), nitrous dioxide (N₂O), and helium (He). The process is then reversed, with methane being used to displace these injected fluids. Time-resolved T₂ distributions are thus able to probe the preference of the methane for smaller or larger pores during these core-flooding processes. In the cases of CO₂ and N₂O, methane was found to preferentially occupy larger pores during both injection and displacement for both rock types. In the case of N₂, no significant preferential pore size occupation was evident, whereas in the case of He, methane preferentially occupied smaller pores. For the fluids used in this work, preferential occupation of comparatively smaller pores during these displacement experiments correlated with a comparatively greater surface adsorption capacity.

中文翻译：

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用NMR T ₂弛豫时间测量评估岩心中的混溶流体驱替

多孔介质中流体的NMR T ₂弛豫时间原则上与相关的占据孔径成正比。在这里，我们利用这种关系来监测甲烷（CH ₄）在100 bar和室温下在砂岩和碳酸盐岩芯中所占的孔径分布，同时它被一系列可混溶的流体（二氧化碳（CO ₂））取代，氮（N ₂），二氧化氮（N ₂ O）和氦气（He）。然后将过程逆转，使用甲烷置换这些注入的流体。时间分辨的T ₂因此，在这些岩心驱替过程中，分布可以探测甲烷对较小或较大孔隙的偏好。在CO ₂和N ₂ O的情况下，发现在两种岩石类型的注入和驱替过程中，甲烷都优先占据较大的孔隙。在N ₂的情况下，没有明显的优先孔径占据明显的迹象，而在He的情况下，甲烷优先占据了较小的孔径。对于这项工作中使用的流体，在这些驱替实验期间优先占据相对较小的孔与相对较大的表面吸附能力相关。