Mineral-Fluid interactions and their implications for the sequestration of CO2 in saline aquifers.

It is known that acidification of reservoirs pore fluids during CO2 subsurface injection leads to fluid-rock interactions. Understanding the effect that these interactions could have on transport and mechanical properties of rocks is particularly relevant for calcite-bearing reservoirs in which rapid pores network evolution could compromise or reinforce the injection operation. In this work, specific experiments were conducted to study the impact of fluid rock interactions on petrophysical properties. The experiments involved the injection into rock cores of CO2-saturated brines to investigate rapid calcite dissolution effects and CO2 plus calcite saturated water to study calcite re-precipitation. Complementary fluid flow modelling at the pore scale was carried out to simulate changes in permeability brought by calcite dissolution. Calcite dissolution directly impacted the permeability and the rock strength in a way that would have been underestimated in classical reservoir simulations. The permeability increase ranged between 50 and 80% while widely used porosity-permeability relationships would predict 10 to 20%, pore scale modelling predictions were found to be more reliable. The change in the rock strength was even more spectacular with a decrease of the shear and bulk moduli of 20% when empirical equations would give a negligible change. Combined experiments and simulations were also used to test the long term CO2 stabilization process known as capillary trapping. The study concluded that CO2 dissolution in brine could give rise to CO2 accumulation in regions of the reservoirs containing larger pores. This could significantly modify CO2 mobility and goes against common belief of capillary trapping stability. This dissertation demonstrate CO2 injection can lead to critical modifications in rock petrophysical properties as well as CO2 trapping processes and that laboratory experiments and pore scale modelling can provide valuable insight into these changes.