The high mobility of CO₂ in porous media is an issue in most subsurface CO₂ projects worldwide, demonstrated by uncontrolled and rapid migration through the reservoir, early well breakthroughs and poor sweep efficiency. Improved mobility control of CO₂ is needed to accelerate and improve the value-creation from subsurface CO₂ projects, both in terms of energy produced and volumes of CO₂ stored. Field-proven conformance and mobility control techniques, such as foam, provide a cost-effective and sustainable alternative to overcome geological and process constraints observed with CO₂ flow in reservoirs.

In this laboratory study, we have investigated CO₂ mobility control by foam in sandstone core samples at typical North Sea reservoir conditions, 220 barg and 100°C, respectively. Two important aspects related to any field application of foam have been evaluated and discussed: I) Can strong CO₂-foams be generated at reservoir conditions using AOS surfactant? If not, II) can relatively simple modifications to the foam system be made to improve foam properties and CO₂ mobility control?

Our results show that only high-mobility CO₂-foams with low degree of CO₂ mobility reduction are obtained at 220 barg and 100°C. An easy way to improve the foam properties at reservoir conditions is suggested by changing the gas-phase in foam to nitrogen (N₂). The N₂-foams display improved foam generation performance, larger mobility control in terms of mobility reduction factors (MRF) and ability to block subsequent CO₂ injection.

An alternative strategy for applying foam for CO₂ conformance and mobility control in subsurface CO₂ projects, which emerges from this study, is to initiate the foam treatment with nitrogen followed by subsequent CO₂ injection to change the main direction of CO₂ flow to enhance the displacement area or reduce uncontrolled CO₂ production between the injecting and producing wells (as illustrated in the graphical abstract). The possible mechanisms explaining the observed differences in foam properties using CO₂ versus N₂, including implications that could be helpful for future studies and CO₂ field applications are discussed further in more detail.

The efficiency and limitations of miscible CO₂ flooding to recover oil and simultaneously store CO₂ after extensive water flooding are also demonstrated in this article, which are relevant to enhanced oil recovery (EOR) and subsequent CO₂ storage applications, known as the Carbon Capture Utilization and Storage (CCUS).

CO ₂在多孔介质中的高流动性是全球大多数地下 CO ₂项目中的一个问题，表现为不受控制的快速迁移通过储层、早期井突破和低波及效率。需要改进 CO _{2 的}流动性控制，以加速和改善地下 CO ₂项目的价值创造，无论是在产生的能量还是储存的 CO ₂量方面。经现场验证的一致性和流动性控制技术，例如泡沫，提供了一种具有成本效益且可持续的替代方案，以克服在储层中观察到的 CO ₂流动的地质和工艺限制。

在本实验室研究中，我们分别研究了在典型的北海油藏条件下（分别为 220 barg 和 100°C）砂岩岩心样品中泡沫对 CO ₂流动性的控制。已经评估和讨论了与泡沫的任何现场应用相关的两个重要方面：I) 可以使用 AOS 表面活性剂在油藏条件下产生强 CO ₂泡沫吗？如果不是，II) 是否可以对泡沫系统进行相对简单的修改以改善泡沫特性和 CO ₂流动性控制？

我们的结果表明，在 220 barg 和 100°C 下只能获得具有低 CO ₂迁移率降低程度的高迁移率 CO ₂泡沫。通过将泡沫中的气相改变为氮气 (N ₂ )，提出了一种在储层条件下改善泡沫特性的简单方法。N _{2 -}泡沫显示出改进的泡沫生成性能、在流动性降低因子(MRF)方面更大的流动性控制以及阻止随后的CO ₂注入的能力。

本研究中出现的在地下 CO ₂项目中应用泡沫进行 CO ₂一致性和流动性控制的另一种策略是用氮气启动泡沫处理，随后注入CO ₂以改变 CO ₂流动的主要方向，以提高置换区域或减少注入井和生产井之间不受控制的 CO ₂产量（如图形摘要所示）。解释使用 CO ₂与 N ₂观察到的泡沫特性差异的可能机制，包括可能有助于未来研究和 CO _{2 的}含义 更详细地讨论了现场应用。

本文还展示了混相 CO ₂驱油在广泛水驱后回收油并同时储存 CO ₂的效率和局限性，这与提高石油采收率 (EOR) 和随后的 CO ₂储存应用有关，称为碳捕集利用和存储 (CCUS)。