The Paris Agreement aim for limiting warming to 1.5 C relies on the assumption that Carbon Capture and Storage will be broadly deployed to reach the Net-Zero emission by 2050. In the last two decades, CO2 storage in saline aquifers has been studied extensively; however, there is an uncertainty with small-scale features just beneath the caprock (surface rugosity and heterogeneity), which will not be identified by seismic data, that could have an effect on plume migration at the top of the storage formation. Thus, considering such effects in a real case scenario such as Sleipner could help further in the prediction of CO2 plume behaviour beneath the caprock. We have investigated the impact of top surface morphology on plume migration using outcrop data in the UK (Sherwood Sandstone Group) then performed a numerical simulation study to examine the impact of reservoir–caprock topography on CO2 plume migration in comparison to other uncertain parameters such as porosity, permeability, reservoir temperature, reservoir pressure and injection rate in the Sleipner using the 2019 Benchmark model.