The geological sequestration of carbon dioxide (CO2) pertains to the permanent storage of CO2 by injecting it into underground structural reservoirs. Saline aquifers are ideal locations for CO2 storage due to their extensive distribution and high storage capacity. Understanding the behavior of CO2 in such geological formations is of paramount importance for the efficient implementation of carbon capture and storage (CCS) strategies. However, many saline aquifers consist of unconsolidated sandstone, and some experimental procedures for exploring the flow behaviors of CO2 are rather challenging. In this study, three plugs of unconsolidated sandstone are selected from a drillhole situated in an offshore basin in China. Modern digital imaging techniques, such as X-ray computed tomography (XCT) and magnetic resonance imaging (MRI), are employed to obtain three-dimensional (3D) pore structures and record the CO2 flow behavior in the plugs during core flooding experiments. This study delves into the intricate relationship between CO2 injection rate, storage capacity, and storage efficiency, revealing a compelling trend. Specifically, as the injection rate of CO2 increases, there is a corresponding enhancement in the storage capacity, enabling a greater volume of CO2 to be trapped. Furthermore, this increased injection rate also leads to an improvement in storage efficiency, indicating that the process becomes more streamlined and effective. In summary, this study underscores the pivotal role of injection rate in optimizing the performance of CO2 sequestration, thereby contributing to more efficient and sustainable CO2 storage solutions. This study also reveals the migration behavior of supercritical CO2 in the connected rock pores from a microscopic scale and provides valuable insights into the fluid dynamics and transport processes of CO2 in the demonstration project of CCS.