Study on two-phase displacement behavior and carbon storage in low-permeability sandstone based on NMR and MRI

Abstract

Deep saline aquifers possess significant potential for carbon storage, and investigating two-phase displacement mechanisms in natural rocks is crucial for achieving efficient and secure CO₂ sequestration. In this study, combined drainage-imbibition displacement experiments were conducted on low-permeability sandstone cores. The two-phase displacement processes were visualized using nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques. A systematic analysis was performed to investigate the influence of heterogeneity and pore structure on displacement patterns. Furthermore, the intrinsic relationships among displacement patterns, displacement efficiency, storage efficiency, and storage security were elucidated. The results showed that the pore structure of the cores significantly affects two-phase displacement behavior and CO₂ storage efficiency. During the displacement process, mesopores and macropores showed higher displacement efficiency and more stable displacement patterns. In contrast, micropores, due to the difficulty of displacing the water and supercritical CO₂ (scCO₂) phases, showed less stable displacement patterns but higher carbon storage efficiency. Cores with better permeability and more uniform pore size distribution tended to exhibit more stable displacement modes, while the scCO₂ phase was more susceptible to the influence of core heterogeneity, leading to less stable displacement compared to the water phase. A higher proportion of macropores in the core led to higher displacement efficiency at the end of the drainage experiments but resulted in the lowest storage efficiency after imbibition. Conversely, cores with higher micropore proportions and less stable displacement during imbibition demonstrated higher final storage efficiency and better storage security. This study provides theoretical guidance for achieving efficient and secure CO₂ storage in deep saline aquifers.