This research investigates how small-scale heterogeneities in rock formations affect CO2 storage in subsurface reservoirs, focusing on core samples from Australia’s Otway CO2 storage site. The study was motivated by observations of unexpected rapid CO2 plume migration at storage projects like Sleipner, which were not predicted by prior modelling efforts.Using medical CT scanning, we imaged steady-state CO2 injection in cores taken from the Otway site. A key finding was that porosity distribution alone couldn’t predict CO2 distribution patterns, as some influential features were smaller than the medical CT scanner’s 0.6mm resolution. The study identified various types of heterogeneities within a 15m interval of the Otway basin, including fine layers, thick layers, and more complex patterns. These different heterogeneities resulted in diverse CO2 distribution and trapping patterns. Importantly, these variations occurred at scales smaller than typical reservoir model grid sizes. The findings contribute to Special Core Analysis (SCAL) for modeling a 10,000-tonne CO2 injection project in the Otway basin, highlighting the importance of incorporating small-scale heterogeneities in reservoir models for accurate prediction of CO2 behaviour.