Carbon dioxide (CO 2 ) capture and subsurface storage is one method for reducing anthropogenic CO 2 emissions to mitigate climate change. It is well known that large-scale fluid injection into the subsurface leads to a buildup in pressure that gradually spreads and dissipates through lateral and vertical migration of water. This dissipation can have an important feedback on the shape of the CO 2 plume during injection, but 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 CO 2 into a layered aquifer system.We develop a compressible, two-phase model that couples pressure dissipation to the propagation of a CO 2 gravity current. We show that our vertically integrated, sharp-interface model is capable of efficiently and accurately capturing water migration in a layered aquifer system with an arbitrary number of aquifers. We identify two limiting cases -'no leakage' and 'strong leakage' -in which we derive analytical expressions for the water pressure field for the corresponding single-phase injection problem. We demonstrate that pressure dissipation acts to suppress the formation of an advancing CO 2 tongue during injection, reducing the lateral extent of the plume. The properties of the seals and the number of aquifers determine the strength of pressure dissipation and subsequent coupling with the CO 2 plume. The impact of pressure dissipation on the shape of the CO 2 plume is likely to be important for storage efficiency and security. * christopher.macminn@eng.ox.ac.uk 1 arXiv:1901.03623v2 [physics.flu-dyn]

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