Since hydrate resources play a part of the stratigraphic framework structure in sediments, establishing a safe and economic method for hydrates exploitation remains the primary challenge to this day. Among the proposed methods, the spontaneous displacement of CH from hydrate cages by CO seems to be a perfect mechanism to address gas production and CO storage, especially in today's strong demand for carbon reduction and replacing clean energy. After extensive lab researches, in the past decade, injecting a mixture of CO and small molecule gas has become a key means to enhance displacement efficiency and has great potential for application. However, there is a lack of in-depth research on gas flow in the reservoir, while the injected gas always passes through low-saturated hydrate areas with high permeability and then occurs gas channel in a short term, finally resulting in the decreases in gas production efficiency and produced gas quality. Therefore, we explored a new injection-production mode of alternate injection of N and CO in order to fully coordinate the advantages of N in enhanced hydrate decomposition and CO in solid storage and heat compensation. These alternate “taking” and “storing” processes perfectly repair the problem of the gas channel, achieving self-regulation effect of CH recovery and CO storage. The 3-D experimental results show that compared to the mixed gas injection, CH recovery is increased by >50% and CO storage is increased by >70%. Additionally, this alternate injection mode presented a better performance in CH concentration of produced gas and showed outstanding N utilization efficiency. Further, we analyzed its self-adaptive gas flow mechanism and proposed an application model of “one injection and multiple production”. We look forward to this study accelerating the application of CO-CH replacement technology.

中文翻译：

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N2和CO2交替注入水合物开采过程中自适应气体流动和相变行为

由于水合物资源是沉积物地层骨架结构的一部分，建立安全、经济的水合物开采方法仍然是当今的首要挑战。在所提出的方法中，CO从水合物笼中自发置换CH似乎是解决天然气生产和CO储存的完美机制，特别是在当今对碳减排和替代清洁能源的强烈需求的情况下。经过大量的实验室研究，近十年来，注入CO和小分子气体的混合物已成为提高驱油效率的关键手段，具有巨大的应用潜力。但目前缺乏对储层气体流动的深入研究，注入气体总是经过高渗透率的低饱和水合物区域，并在短期内形成气道，最终导致天然气储量减少。生产效率和产气质量。为此，我们探索了N2和CO交替注入的注采新模式，以充分协调N2强化水合物分解和CO2固体储存和热量补偿的优势。这些交替的“取”和“储”过程完美修复了气体通道的问题，实现了CH回收和CO封存的自我调节效果。 3D实验结果表明，与混合注气相比，CH回收率提高了>50%，CO储存量提高了>70%。此外，这种交替注入模式在产气CH浓度方面表现出更好的性能，并表现出出色的N利用率。进一步分析了其自适应气流机理，提出了“一次注多产”的应用模式。我们期待这项研究加速CO-CH替代技术的应用。