The high affinity and adsorption capacity of coal to carbon dioxide provides an alternative approach for the enhanced recovery of methane from unminable coalfields (CO₂-ECBM) by which a potential solution for long-term CO₂ sequestration in deep geological formations can also be achieved. However, due to chemomechanical effects induced by the interactions between CO₂ and coal, the effective methane production and carbon dioxide storage can be degraded which has caused uncertainties about the techno-economic feasibility of the CO₂-ECBM process. This study presents an experimental investigation that aims to address key knowledge gaps related to the efficiency of CO₂ storage and CH₄ recovery in high rank coals for which a comprehensive experimental data set and analysis are largely missing. Competitive displacements of CH₄ with N₂ or CO₂ in an anthracite coal sample from a South Wales coalfield have been studies, based on a series of core flooding experiments. The results show that the N₂ breakthrough time (the time at which 1% of the total gas injected was recovered) was almost spontaneous whereas a considerably delayed breakthrough time was observed for the case of the CO₂-ECBM experiment. In addition it was observed that for the CO₂-ECBM experiment, the ratios of CH₄ recovery with respect to the total amount of gas injected and gas stored were higher by factors of 10 and 2.4, respectively. The results also show that 90% of the total N₂ injected was produced in the outflow gas, whereas for the case of the CO₂ experiment, only 63% of the total injected CO₂ was produced. The presence of a high amount of N₂ in the outflow may lead to additional challenges in order to separate N₂ from CH₄ and thus affect the efficiency of the N₂-ECBM method. Under the conditions of the experiments, the total CH₄ displacement ratio and breakthrough for the case CO₂-ECBM were found to be more favorable compared to those obtained from N₂-ECBM. This study provides new insights into the efficiency of the CO₂-ECBM process and offers a comprehensive experimental data set that can be used for testing the accuracy of predictive models.

中文翻译：

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高阶煤中二氧化碳的储存效率和提高的甲烷回收率

煤对二氧化碳的高亲和力和吸附能力为提高从不可开采煤田中的甲烷（CO ₂ -ECBM）采收率提供了另一种方法，通过这种方法，也可以实现在深部地质构造中长期固存CO ₂的潜在解决方案。然而，由于由CO ₂和煤之间的相互作用引起的化学机械作用，有效的甲烷生产和二氧化碳的储存可能会降低，这导致了对CO ₂ -ECBM工艺的技术经济可行性的不确定性。这项研究提出了一项实验研究，旨在解决与CO ₂储存和CH ₄效率相关的关键知识空白缺少全面的实验数据集和分析的高品位煤的采收率。基于一系列岩心驱油实验，已经研究了来自南威尔士煤田的无烟煤样品中CH ₄与N ₂或CO _2的竞争性驱替。结果表明，N ₂穿透时间（回收注入的总气体的1％的时间）几乎是自发的，而对于CO ₂ -ECBM实验，则观察到了相当大的延迟穿透时间。另外，观察到对于CO ₂ -ECBM实验，CH ₄的比率相对于注入的气体总量和存储的气体总量，回收率分别提高了10倍和2.4倍。结果还表明，注入的总N _2的90％是在流出气体中产生的，而对于CO ₂实验，则只有注入的总CO _2的63％产生了。为了将N ₂与CH ₄分离，流出物中大量N ₂的存在可能会带来其他挑战，从而影响N ₂ -ECBM方法的效率。在实验条件下，CO ₂的总CH ₄置换率和突破与从N ₂ -ECBM获得的那些相比，发现-ECBM更有利。这项研究提供了对CO ₂ -ECBM工艺效率的新见解，并提供了可用于测试预测模型准确性的综合实验数据集。