Migrazione di CO2 in strutture geologiche profonde: modelli e metodi numerici

The fight against global warming is a task that has recently been addressed by many different studies. Among all the approaches designed to reduce the amount of atmospheric CO2, the Carbon Capture and Sequestration (CCS) technique is receiving a lot of credit. However, we are still unaware of the consequences of storing a massive amount of CO2 in deep geological structures. For this reason, it is important to be able to simulate the long-time behaviour of fluid mixtures containing CO2 once stored. %SCHIFO We detail the mathematical model describing the flow of these mixtures inside a porous medium. The equations in this model cannot be analytically solved. We then adopt a numerical approach, based on the Integrated Finite Difference Method (IFDM). This leads to a system of non-linear coupled equations, solvable through Newton-Raphson method, in which the time step is chosen by an adaptive algorithm. The TMGAS software developed by ENI S.p.A. implements the IFDM. However, the method shows numerical instabilities which cause repeated reductions of the time step. The averaging and upwinding techniques used to evaluate the thermodynamic parameters at the interface between grid blocks seem to be the origin of these instabilities. In this thesis, we describe the abovementioned model and we gather the main contributions established in this field.