Hydrodynamic Analysis of CO₂ Migration in Heterogeneous Rocks: Conventional and Micro‐Bubble CO₂ Flooding Experiments and Pore‐Scale Numerical Simulations

Abstract

Abstract The hydrodynamics of CO 2 flooding determine its capacity and efficiency in CO 2 geological storage; however, this is not sufficiently understood. In this study, a medical X‐ray CT was used to visualize CO 2 flooding in a Berea sandstone sample, and the migration pattern and distribution of injected CO 2 were carefully analyzed in a series of comparison experiments. For conventional flooding, CO 2 migrated mostly along the high‐porosity and large‐pore‐size layers, leaving a large area of low‐porosity and small‐pore‐size regions undisplaced. Comparatively, before CO 2 broke through, CO 2 fingering developed and migrated slowly for micro‐bubble flooding, showing that CO 2 micro‐bubbles infiltrated into more regions than the CO 2 continuous fluid. After CO 2 breakthrough began, the micro‐bubble CO 2 continued to enter some previously undisplaced regions; however, this was inconspicuous for conventional flooding. Finally, micro‐bubble flooding increased CO 2 saturation by 6.1% over conventional flooding. Compared to conventional flooding, an essential hydrodynamic change by micro‐bubble flooding weakened the resistance of interface tension over CO 2 infiltration into the small pores. Accordingly, two types of hydrodynamic models were proposed for conventional and micro‐bubble CO 2 flooding, and their simulated pore‐scale CO 2 migration results in a cluster of heterogeneous pores were compatible with the aforementioned core‐scale experimental observations. According to these models, both the small sizes and high injection rates of micro‐bubble CO 2 were instrumental in enhancing the displacement effect. The filter for micro‐bubble CO 2 injection in our experiment achieved even injection of the small CO 2 micro‐bubbles at a relatively high rate, ensuring its practical potential in field applications.

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