Numerical modelling of the hydro-chemo-mechanical behaviour of geomaterials in the context of CO2 injection

Abstract : Safety assessment of geosequestration of CO2 into deep saline aquifers requires a precise understanding of the study of hydro-chemo-mechanical couplings occurring in the rocks and the cement well. To this aim, a coupled chemo-poromechanical model has been developed and implemented into a research code well-suited to the resolution of fully coupled problems. This code is based on the finite volume methods. In a 1D axisymmetrical configuration, this study aims to simulate the chemo-poromechanical behaviour of a system composed by the cement well and the caprock during CO2 injection. Major chemical reactions of carbonation occurring into cement paste and rocks are considered in order to evaluate the consequences of the presence of CO2 on the amount of dissolved matrix and precipitated calcium carbonates. The dissolution of the solid matrix is taken into account through the use of a chemical porosity. Matrix leaching and carbonation lead, as expected, to important variations of porosity, permeability and to alterations of transport properties and mechanical stiffness. These results justify the importance of considering a coupled analysis accounting for the main chemical reactions. It is worth noting that the modelling framework proposed in the present study could be extended to model the chemo-poromechanical behaviour of the reservoir rock and the caprock when subjected to the presence of an acidic pore fluid (CO2-rich brine).