Pore-scale Simulations of Haines Jump and Capillary Filling in Randomly Distributed Pore Structures with Implications for CO₂ Geological Storage

Abstract

Studying the mechanisms embedded in the immiscible displacement of the two-phase fluids has many engineering and natural implications, like the CO₂ geological storage, the secondary or ternary oil and gas recovery and the NAPL remediation in underground formations. The pore-scale phenomena such as Haines jump and capillary filling are recognized in the literatures to have a strong impact on the displacement phenomena. Haines jump is characterized by an abrupt jump of some certain two-phase interfaces while rearranging the configuration of the meniscus of the surrounding pores. In contrast, the capillary filling induces a flat interface movement, where non-wetting phase fluid favors the larger pores due to capillary forces, and vice versa. In this article, we have simulated the drainage process in randomly distributed pore structures with varied pore throat diameters. The Haines jump and capillary filling phenomena are recognized to play a significant role in the saturation and frontal position curves. As a result, Haines jump tends to induce a hop of frontal position given the same saturation, whereas the capillary filling evades pore spaces with a fixed frontal position. In addition, the influence of capillary number and viscosity ratio are thoroughly analyzed. The result shows that higher capillary number and higher viscosity ratio are deemed favorable for the entrapment of non-wetting phase fluid (like CO₂). The energy equilibrium study shows around 48% of the external input work is dissipated through these instantaneous irreversible events. Ways to reduce the occurrence of these events will undoubtedly increase the displacement energy efficiency. This work has a direct implication for CO₂ geological storage.