Microbubble and Conventional CO ₂ Injections and Their Impacts on Carbon Sequestration Efficiency

The success of geological CO2 sequestration depends on efficient injection methods and effective pore-scale displacement and stable long-term trapping of CO2 within reservoir rocks. The effectiveness of residual trapping as a containment security mechanism depends on how CO2 moves through and fills the subsurface pore network. This study comprehensively investigated CO2 microbubble injection (MBI) and conventional supercritical CO2 injection (CI) under reservoir conditions in heterogeneous Otway Basin sandstone before the real field experiment. The research used different techniques including nuclear magnetic resonance (NMR), micro-CT, and SCAL measurements to study pore-scale displacement behavior, pore accessibility, and CO2 storage capacity. MBI and CI injections were broadly evaluated on different rock types through measurements of breakthrough time, pressure-drop trends, sweep efficiency, pore accessibility, CO2 storage capacity, residual trapping, capillary pressure, and relative permeability curves. The results showed that CO2 injection through conventional methods mainly fills large pores, which leads to inferior sweep efficiency and weaker trapping capabilities. However, the MBI method produced better CO2 distribution, improved pore connectivity, and deeper penetration into tight pores resulted in better initial saturation and stronger capillary trapping. The extended breakthrough time, reduced gas channelling, and lower capillary entry pressure indicate that MBI produces a more stable and efficient displacement front, which makes MBI an effective new approach for secure CO2 storage in heterogeneous and low-permeability rock formations.