Mechanistic Insights into Hydrate-Based CO ₂ Sequestration in Methane Hydrate-Bearing Porous Media via MRI-Enabled Nondestructive Analysis

To mitigate climate change, hydrate-based CO2 storage in high-pressure and low-temperature geological settings has emerged as a promising negative emission strategy. However, conventional observation methods are inadequate for capturing the real-time dynamics of hydrate formation and spatial distribution in porous media, thereby constraining accurate evaluation of storage capacity and long-term stability. In this study, methane hydrate-bearing porous media were employed to simulate natural gas hydrate reservoir conditions, and magnetic resonance imaging was used for in situ, nondestructive visualization of CO2 seepage and hydrate evolution during storage at 274.15 K and 3.0 MPa. The results showed that newly formed CO2 hydrates can develop into an effective sealing layer that significantly suppresses large-scale water migration beneath it. Nevertheless, the layer was not fully compact; and the presence of micropores allows slow redistribution of the aqueous phase, leading to a cyclic process of dynamic breakthrough, gas release, and regeneration. Moreover, midstage injection of single-phase water was shown to reopen local seepage pathways, not only alleviating blockage but also enlarging the CO2–water contact area, thereby enhancing the ultimate storage performance. Quantitatively, the maximum CO2 storage capacity reached 0.039 mol, and the corresponding storage rate was 0.0099 mol/h under the higher initial hydrate saturation condition. These findings provide mechanistic insight into hydrate-based CO2 sequestration in methane hydrate-bearing reservoirs and offer theoretical support for condition optimization, long-term stability assessment, and the future development of larger-scale monitoring approaches.