Title: Direct observation of coupled geochemical and geomechanical impacts on chalk microstructural evolution under elevated CO2 pressure. Part I,
Abstract: The dissolution of porous media in a geologic formation induced by the
injection of massive amounts of CO2 can undermine the mechanical stability of
the formation structure before carbon mineralization takes place. The
geomechanical impact of geologic carbon storage is therefore closely related to
the structural sustainability of the chosen reservoir as well as the
probability of buoyancy driven CO2 leakage through caprocks. Here we show, with
a combination of ex situ nanotomography and in situ microtomography, that the
presence of dissolved CO2 in water produces a homogeneous dissolution pattern
in natural chalk microstructure. This pattern stems from a greater apparent
solubility of chalk and therefore a greater reactive subvolume in a sample.
When a porous medium dissolves homogeneously in an imposed flow field, three
geomechanical effects were observed: material compaction, fracturing and grain
relocation. These phenomena demonstrated distinct feedbacks to the migration of
the dissolution front and severely complicated the infiltration instability
problem. We conclude that the presence of dissolved CO2 makes the dissolution
front less susceptible to spatial and temporal perturbations in the strongly
coupled geochemical and geomechanical processes.