Summary Carbon dioxide (CO2) enhanced oil recovery (EOR) has long been practiced in the US as an efficient mean for enhancing oil production. Many of the US CO2-EOR developments have been designed horizontally. This is because of a viscous-dominated CO2 flow regime that is prevalent in these developments driven by thin and low-permeability reservoirs. Reservoirs and fluid properties are different in the North Sea. Pays are usually thicker with better petrophysical properties. Lighter oils can also be found in North Sea reservoirs. This suggests that a dissimilar flow regime might prevail CO2 displacements in the North Sea developments, which could favor a dissimilar CO2-EOR process design. This study thus compares CO2 flow regimes between several North Sea and US reservoirs. We use scaling analysis to characterize and compare CO2 flow regimes between these two classes of reservoirs. Scaling analysis characterizes CO2 displacement in each reservoir system using three dimensionless numbers: gravity, effective aspect ratio, and mobility ratio. Displacement experiments conducted in stochastically generated permeability fields, under exactly matched magnitudes of the derived dimensionless numbers, reveal the prevailing CO2 flow regime in each reservoir system. Results of scaling analysis indicate that CO2 flooding in the North Sea reservoirs can be generally characterized with a larger gravity number, smaller effective aspect ratio, and smaller mobility ratio than the average US CO2 flooded reservoirs. Flow regime analysis indicates that unlike the majority of the US CO2 flooded reservoirs, CO2 flow regimes tend to be more gravity-dominated in the North Sea class of reservoirs. CO2 flow regimes in the North Sea systems are expected to suffer from a higher degree of instability because of thicker North Sea pays, which limit effective crossflow. Understanding the differences and characteristics of CO2 flow regimes in the North Sea prospects can help operators design their CO2 flooding more efficiently, which could increase the recovery factor (RF) as well as address CO2 storage requirements, a necessary consideration for CO2-EOR deployment in the North Sea.

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北海和美国储层的二氧化碳流动状态比较

总结 二氧化碳 (CO2) 提高石油采收率 (EOR) 在美国长期以来一直被用作提高石油产量的有效手段。美国的许多 CO2-EOR 开发项目都是横向设计的。这是因为在这些由薄而低渗透率储层驱动的开发中普遍存在以粘性为主的 CO2 流动状态。北海的储层和流体性质不同。具有更好的岩石物理特性的薪水通常更厚。在北海油藏中也可以找到较轻的油。这表明，在北海开发项目中，不同的流动状态可能占主导地位，这可能有利于不同的 CO2-EOR 工艺设计。因此，本研究比较了几个北海和美国水库之间的二氧化碳流态。我们使用比例分析来表征和比较这两类储层之间的 CO2 流动状态。比例分析使用三个无量纲数来表征每个油藏系统中的 CO2 驱替：重力、有效纵横比和流度比。在随机生成的渗透率场中进行的驱替实验，在推导的无量纲数的大小完全匹配下，揭示了每个储层系统中普遍存在的 CO2 流动状态。尺度分析结果表明，与美国CO2 驱油藏相比，北海油藏CO2 驱总体具有重数大、有效纵横比小、流度比小的特点。流态分析表明，与美国大多数二氧化碳淹没的水库不同，在北海类储层中，CO2 流动状态往往更受重力支配。预计北海系统中的二氧化碳流态将遭受更高程度的不稳定性，因为北海层较厚，这限制了有效的横流。了解北海远景中 CO2 流态的差异和特征可以帮助运营商更有效地设计其 CO2 驱油，这可以提高采收率 (RF) 并满足 CO2 储存要求，这是部署 CO2-EOR 的必要考虑因素北海。