Impact of pressure dissipation on fluid injection into layered aquifers

It is well known that large-scale fluid injection into the subsurface leads to a buildup in pressure that gradually spreads and dissipates through diffusive lateral and vertical migration of brine. In carbon dioxide (CO₂) capture and storage, this pressure buildup and dissipation can have an important feedback on the shape of the CO₂ plume during injection. The impact of vertical pressure dissipation, in particular, remains poorly understood. Here, we investigate the impact of lateral and vertical pressure dissipation on the injection of CO₂ into a layered saline aquifer. We develop a theoretical model that couples vertical brine leakage to the propagation of a CO₂ gravity current. We show that our vertically integrated, sharp-interface model is capable of efficiently and accurately capturing brine migration in layered aquifers. We identify two limiting cases - ‘no leakage’ and ‘strong leakage’ - in which we derive analytical expressions for the brine pressure field in the corresponding single-phase injection problem. We demonstrate that pressure dissipation acts to suppress the formation of an advancing CO₂ tongue, resulting in a plume with a reduced lateral extent. The impact of pressure dissipation on the shape of the CO₂ plume is likely to be important for storage efficiency.