Abstract The choice of the flow velocity in EGR thus becomes important since higher injection rates could lead to premature mixing of the fluids and lower injection rates generally provide longer resident times for the fluids in contact and indirectly increases the mixing of the gases. Additionally, the medium peclet numbers mostly indicate the best injection rates that translate to a smoother displacement with a lower dispersion coefficient during the EGR process. Therefore, N2 Injection into natural gas reservoirs offers the potential to higher recovery efficiency with less mixing compared to conventional CO2 injection. The atmospheric air contained 79% of N2, making it readily available than CO2 with 400 ppm air composition. More so, N2 requires less compression ratio, which is why a lower amount of it was required to initiate much pressure in the CH4 reservoir during displacement. These made the use of N2 more economically feasible and friendly for the EGR process. A laboratory core flooding experiment was carried out to simulate the effect of injection velocity on CH4 recovery and dispersion coefficient. This was done at 40 °C, 1500 psig, and 0.2–1.0 ml/min injection rates. The results showed that a medium peclet number could be used to predict the best injection rate that translates to a smoother displacement with a lower dispersion coefficient during the EGR process. CH4 recovery and efficiency were highest at lower injection velocities experienced in both core samples. This could be attributed to insignificance nascent mixing observed as seen on their recorded low longitudinal dispersion coefficient results. Consequence, the experimental runs at high injection rates (0.6–1.0 ml/min) present a different scenario with lower recovery and efficiency due to their high interstitial velocities as the N2 plumes transverses into the core sample during CH4 displacement. Overall, the least methane production and efficiency were noticed in the Bandera core sample as a result of the heterogeneity effect due to the presence of higher clay contents in Bandera than Berea gray. When the capillary forces within the narrower pores in Bandera core sample were overcome, the clay particles occupied those pores thereby sealing some of the flow paths within the pore matrix. This reduces the flow channels, significantly, through which the injected N2 will flow to displace the residual CH4.

中文翻译：

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通过注氮提高天然气采收率：注入速度对固结岩中天然气驱替的影响

摘要 因此，EGR 中流速的选择变得很重要，因为较高的喷射率可能导致流体过早混合，而较低的喷射率通常为接触的流体提供更长的停留时间并间接增加气体的混合。此外，中等 peclet 数主要表明最佳喷射率，这转化为在 EGR 过程中具有较低分散系数的更平滑的位移。因此，与传统的 CO2 注入相比，向天然气储层注入 N2 具有更高的采收率和更少的混合潜力。大气中含有 79% 的 N2，使其比空气成分为 400 ppm 的 CO2 更容易获得。更重要的是，N2 需要更少的压缩比，这就是为什么在驱替过程中在 CH4 储层中启动大量压力所需的量较少。这使得使用 N2 在 EGR 过程中更加经济可行和友好。进行了实验室岩心驱油实验以模拟注入速度对 CH4 采收率和分散系数的影响。这是在 40 °C、1500 psig 和 0.2–1.0 ml/min 注射速率下完成的。结果表明，中等佩克莱数可用于预测最佳喷射率，该喷射率转化为在 EGR 过程中具有较低分散系数的更平滑的位移。两种岩心样品在较低注入速度下的 CH4 回收率和效率最高。这可能是由于在其记录的低纵向色散系数结果中观察到的新生混合微不足道。结果，在高注入速率 (0.6-1.0 ml/min) 下的实验运行呈现出不同的情况，由于在 CH4 置换过程中 N2 羽流横向进入岩心样品时间隙速度高，因此回收率和效率较低。总体而言，班德拉岩心样品中的甲烷产量和效率最低，这是由于班德拉岩心比 Berea 灰岩中粘土含量更高而产生的非均质性效应。当班德拉岩心样品中较窄孔隙内的毛细管力被克服时，粘土颗粒占据了这些孔隙，从而密封了孔隙基质内的一些流动路径。这大大减少了流动通道，