Pore-scale synchrotron imaging of scCO2-brine intermittent flow: Experimental insights into multiphase dynamics for geological carbon storage

Underground carbon dioxide (CO 2 ) storage is a critical approach for mitigating climate change by sequestering CO 2 in deep geological formations. The interaction between injected super critical (sc) CO 2 and resident brine within pores results in complex two-phase flow dynamics that influence the efficiency and security of storage. While previous studies have mainly focused on capillary-dominated regimes, where fluid phases flow at low velocities, the transitional intermittent flow regime—characterised by higher flow rates and complex displacement dynamics—remains less understood. This study investigates the onset and development of intermittent flow pathways in CO 2 -brine systems through high-resolution synchrotron X-ray micro-computed tomography imaging of a carbonate rock sample. The core-flooding experiments were conducted under 8 MPa and 50 °C to examine pore-scale fluid configuration changes as a function of capillary number ( Ca ). The results indicate that intermittent flow emerges at lower Ca values than previously observed in oil-brine systems, with a distinct transition from Darcy flow to intermittent flow. Moreover, the saturation of the intermittent phase stabilises beyond a threshold Ca , suggesting another phase transition within the intermittent flow regime. These findings provide new insights into the fundamental mechanisms of two-phase flow dynamics at the pore scale, revealing a stable intermittent flow regime at higher flow rates, with potential implications for improved injectivity under non-equilibrium conditions. • First experimental visualisation of scCO 2 –brine intermittency using synchrotron X-ray micro-CT imaging in carbonate rock. • Intermittency saturation rises and levels off near 39% once Ca exceeds ∼1.77×10⁻⁷, marking a distinct flow-regime shift. • Intermittency thresholds match theory, supporting models for CO₂ injection planning and storage efficiency.