Impact of Groundwater Flow Direction on Early CO₂ Plume Migration in Dipping Aquifers

The direction of groundwater flow can affect CO₂ plume migration, and hence the storage characteristics. Using numerical modeling, we compare the early post-injection evolution of the CO₂ plume in a synthetic dipping aquifer under different directions of groundwater flow. We measure the size of the plume, its mobile portion as well as the instantaneous velocity at its leading tip. The study shows the direction of groundwater flow can affect the extent and evolution of the CO₂ plume during and post injection. When the groundwater flows downdip, opposite to the direction of CO₂ plume, the plume stretches further during its upward migration compared to the updip groundwater flow scenario. This increases the extent of the mobile CO₂ and causes the plume to accelerate during updip migration due to the greater acting buoyancy forces. In contrast, when groundwater flows updip, in the same direction as the plume migration, the plume decelerates due to the combined effects of greater residual and dissolution trapping, which decrease the size of the mobile CO₂, and reduced buoyancy due to the smaller size of the mobile plume. Hence, an updip groundwater flow can better reduce the risk of CO₂ leakage during its early migration.