Abstract Underground gas storage (UGS) is an industrial process used for compensating the supply and demand chain for natural gas in different seasons of the year. In this process, the excess natural gas produced in summer is injected into an underground reservoir to be harvested in winter. This porous medium also might contain an in situ gas which can be used as the cushion gas. The presence of a non-hydrocarbon gas (e.g. nitrogen) in the reservoir prior to the UGS process could have advantages and disadvantages during the process. If natural gas is injected as the cushion gas, the operational costs will be high. Besides, a significant advantage of nitrogen as the cushion gas is the reduction of preparation time defined as the initial injection period. The presence of nitrogen in the formation also increases the reservoir pressure, which results in a higher rate and pressure during production periods. However, a higher initial reservoir pressure causes lower gas injectability in the storage process; hence, during injection periods, the volume of injected gas is reduced. In addition, an unexpected mixing of cushion gas with the injected gas reduces the quality and heating value of gas. Therefore, a separation unit is required and more operational costs are expected. In this work, a reservoir located in Middle East with great nitrogen volume is selected. Based on the physical properties of the reservoir, a simulation by ECLIPSE 300 is made and the advantages and disadvantages of nitrogen existence in the process of UGS is analyzed, from technical and economical point of view. The presence of nitrogen saves millions of dollars due to reduction of preparation time and costs. Besides, an unwanted mixing of nitrogen with natural gas, causes millions of dollars loss of gas value due to reduction in gas market value and nitrogen separation.

中文翻译：

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地下储气库 (UGS) 过程中原位 N2 存在的优缺点：案例研究的技术和经济评估

摘要 地下储气库（UGS）是一种用于补偿一年中不同季节天然气供需链的工业过程。在这个过程中，夏季产生的多余天然气被注入地下储层，在冬季进行采收。这种多孔介质也可能包含可用作缓冲气体的原位气体。在 UGS 过程之前，储层中存在非烃气体（例如氮气）在该过程中可能具有优点和缺点。如果注入天然气作为缓冲气，运行成本会很高。此外，氮气作为缓冲气体的一个显着优点是减少了定义为初始注入期的准备时间。地层中氮的存在也增加了储层压力，这导致在生产期间更高的速率和压力。然而，较高的初始储层压力导致储存过程中较低的气体注入能力；因此，在注入期间，注入的气体量减少。此外，缓冲气体与注入气体的意外混合会降低气体的质量和热值。因此，需要一个分离单元，预计会有更多的运营成本。在这项工作中，选择了位于中东的一个氮量大的水库。根据储层物性，利用ECLIPSE 300进行模拟，从技术经济角度分析了UGS过程中氮存在的优缺点。由于减少了制备时间和成本，氮气的存在可节省数百万美元。