CO 2 Dissolution Trapping Rates in Heterogeneous Porous Media

The rate of carbon dioxide (CO 2 ) dissolution in saline aquifers is the least well‐constrained of the secondary trapping mechanisms enhancing the long‐term security of geological carbon storage. CO 2 injected into a heterogeneous saline reservoir will preferentially travel along high permeability layers increasing the CO 2 ‐water interfacial area which increases dissolution rates. We provide a conservative, first‐principles analysis of the quantity of CO 2 dissolved and the rate at which free‐phase CO 2 propagates in layered reservoirs. At early times, advection dominates the propagation of CO 2 . This transitions to diffusion dominated propagation as the interfacial area increases and diffusive loss slows propagation. As surrounding water‐filled layers become CO 2 saturated, propagation becomes advection dominated. For reservoirs with finely bedded strata, ∼ 10% of the injected CO 2 can dissolve in a year. The maximum fraction of CO 2 that dissolves is determined by the volumetric ratio of water in low permeability layers and CO 2 in high permeability layers.