Comparison between downdip and updip groundwater flow on early CO₂ migration in dipping storage aquifers

The impact of the aquifer dip angle and groundwater flow have been investigated in the field of carbon dioxide (CO₂) storage efficiency and security. However, no consideration has been given to the significance of the direction of groundwater flow in aquifers on the CO₂ plume migration and the storage performance. In this study, we analyse the effect of the direction of groundwater flow on CO₂ plume migration in the subsurface, implementing a numerical modelling approach. We compare the early plume migration in storage aquifers of various dip angles when the groundwater flows downdip with when it flows updip. We estimate the injected plume size, and the instantaneous velocity of the leading tip of the plume. When the groundwater flows downdip, against the direction of CO₂ plume migration, the plume becomes more stretched, its greater extent and thus height causing it to accelerate during its updip migration due to the increase in buoyancy. By contrast, the plume decelerates over time when groundwater flows updip. This is because of a decrease in the size of the mobile CO₂ plume due to enhanced residual and dissolution trapping at its trailing edge, reducing buoyancy, and hence decreasing the risk of CO₂ leakage during its early migration.