  When carbon dioxide (CO2) is injected into an aquifer or a depleted
geological reservoir, its dissolution into solution results in acidification of
the pore waters. As a consequence, the pore waters become more reactive, which
leads to enhanced dissolution-precipitation processes and a modification of the
mechanical and hydrological properties of the rock. This effect is especially
important for limestones given that the solubility and reactivity of carbonates
is strongly dependent on pH and the partial pressure of CO2. The main mechanism
that couples dissolution, precipitation and rock matrix deformation is commonly
referred to as intergranular pressure solution creep (IPS) or pervasive
pressure solution creep (PSC). This process involves dissolution at
intergranular grain contacts subject to elevated stress, diffusion of dissolved
material in an intergranular fluid, and precipitation in pore spaces subject to
lower stress. This leads to an overall and pervasive reduction in porosity due
to both grain indentation and precipitation in pore spaces. The percolation of
CO2-rich fluids may influence on-going compaction due to pressure solution and
can therefore potentially affect the reservoir and its long-term CO2 storage
capacity. We aim at quantifying this effect by using a 2D numerical model to
study the coupling between dissolution-precipitation processes, local mass
transfer, and deformation of the rock over long time scales. We show that high
partial pressures of dissolved CO2 (up to 30 MPa) significantly increase the
rates of compaction by a factor of ~ 50 to ~ 75, and also result in a
concomitant decrease in the viscosity of the rock matrix.

Geophysics