The role of injection rate in enhancing $${\textrm{CO}}_2$$ capillary trapping in saline aquifer systems

As the energy industry transitions toward net-zero emissions, underground carbon dioxide ( $$\textrm{CO}_2$$ ) storage plays a crucial role in mitigating global warming caused by anthropogenic $$\textrm{CO}_{2}$$ emissions. Capillary trapping is considered one of the most promising mechanisms for $$\textrm{CO}_2$$ storage in saline aquifer systems. It is essential for securely immobilizing $$\textrm{CO}_2$$ in porous rock formations, improving the long-term stability of geological storage. The lack of understanding of factors affecting the contribution of capillary trapping in sequestration may result in only partial achievement of technical and financial objectives. In this study, the mutual relationship between injection rates, initial saturation of $$\textrm{CO}_2$$ , and capillary trapping capacity was studied by performing displacement experiments on a micromodel representing a heterogeneous sandstone aquifer. The brine-alternating- $$\textrm{CO}_2$$ (BAC) technique was applied under varying injection conditions of brine and proxy supercritical $$\textrm{CO}_2$$ ( $${\textrm{ScCO}}_2$$ ) into the micromodel. In this study, it was observed that large clusters of trapped $$\textrm{CO}_2$$ were developed due to the dominance of capillary forces at lower injection rates of brine, resulting in a trapped $$\textrm{ScCO}_2$$ saturation of 0.62. However, the saturation of trapped $${\textrm{proxyScCO}}_2$$ was decreased to 0.37 due to the increasing influence of viscous forces at higher injection rates. This study highlights the crucial role of capillary and viscous forces during BAC injection in heterogeneous sandstone reservoirs and provides a guideline for laboratory-scale $$\textrm{ScCO}_2$$ sequestration studies.