To realize the transition of our society to a low-carbon future with innovative subsurface energy solutions, understanding the dynamic behavior of gas invading multi-fluid systems in underground pore space is critical. In this work, a joint approach of flow imaging and digital image processing is employed to investigate the fingering dynamics of gas invading multi-fluids in porous media. We examined various gas (G) invasion scenarios of a high-viscosity defending liquid (HL), low-viscosity defending liquid (LL), and their co-existing multi-fluid system, focusing on the viscosity effect. Quantification of phase saturation shows that the displacement efficiency follows the order of G(LL) LL GL, regardless of the varieties in injection flow rate in the viscous-dominated flow regime. In other words, the enhancement in displacement efficiency and potential energy savings are achieved by solely introducing a third phase without the cost of the higher pumping power. When gas invades the HL and LL multi-liquid system, the fingering pattern in G(HLLL) and G(LLHL) significantly differs and highly depends on the sequential occupation of HL and LL in the pore spaces. The previously unobserved yarn-liked gas pattern in G(LLHL) is suspected as the main reason for the fast gas displacement. Through Local dynamics analysis, we identified that the preferential invasion into interconnected LL channels and the inhibitory effect of scattered HL on bypass invasion are the primary mechanisms behind the formation of yarn-liked fingers. We classified two distinct categories of ganglia mobilization and connection in G(LLHL), i.e. “catch up to connect” and “expand to connect”. Finally, the topological connectivity of the gas finger in G(LLHL) is evaluated using Euler number. Euler number shows an ascending trajectory before breakthrough, followed by a rapid descent and stabilization at steady state. This signifies that disconnected ganglia emerge before breakthrough and subsequently expand and reconnect. Our new findings are of great importance for subsurface extraction/storage strategy innovation through enriching multi-fluids injection scenarios.

中文翻译：

---

气体侵入多流体的粘性相关指进动力学


为了通过创新的地下能源解决方案实现我们的社会向低碳未来的转变，了解地下孔隙空间中气体侵入多流体系统的动态行为至关重要。在这项工作中，采用流成像和数字图像处理的联合方法来研究多孔介质中气体侵入多流体的指进动力学。我们研究了高粘度防护液体（HL）、低粘度防护液体（LL）及其共存的多流体系统的各种气体（G）入侵场景，重点关注粘度效应。相饱和度的量化表明，无论粘性主导流态中注入流量的变化如何，驱替效率都遵循 G(LL) LL GL 的顺序。换句话说，仅通过引入第三阶段即可实现驱替效率的提高和潜在的节能，而无需付出更高泵送功率的成本。当气体侵入 HL 和 LL 多液体系统时，G(HLLL) 和 G(LLHL) 中的指进模式显着不同，并且高度依赖于 HL 和 LL 在孔隙空间中的顺序占据。 G(LLHL) 中先前未观察到的纱线状气体模式被怀疑是快速气体置换的主要原因。通过局部动力学分析，我们发现优先侵入相互连接的 LL 通道和分散的 HL 对旁路侵入的抑制作用是纱线状手指形成背后的主要机制。我们将 G(LLHL) 中的神经节动员和连接分为两个不同的类别，即“赶上连接”和“扩展连接”。最后，使用欧拉数评估 G(LLHL) 中气体指的拓扑连通性。 欧拉数显示突破前的上升轨迹，随后快速下降并稳定在稳态。这意味着断开的神经节在突破之前出现，随后扩展并重新连接。我们的新发现对于通过丰富多流体注入场景进行地下提取/存储策略创新具有重要意义。