Soft Matter and Complex Systems Seminar

In a context of international reduction of greenhouse gases emissions, CCS (CO2 Capture and Storage) appears as a particularly interesting midterm solution. Indeed, geological storage capacities may raise to several millions of tons of CO2 injected per year, allowing to reduce substantially the atmospheric emissions of this gas. One of the most interesting targets for the development of this solution are the deep saline aquifers. These aquifers are geological formations containing brine whose salinity is often higher than sea water's, making it unsuitable for human consumption. However, this solution has to cope with numerous technical issues, and in particular, the precipitation of salt initially dissolved in the aquifer brine. Consequences of this precipitation are multiple, but the most important is the modification of the injectivity i.e. the injection capacity. Knowledge of the influence of the precipitation on the injectivity is particularly important for both the storage efficiency and the storage security and durability. The aim of this PhD work is to compare the relative importance of negative (clogging) and positive (fracturing) phenomena following CO2 injection and salt precipitation. Because of the numerous simulations and modelling results in the literature describing the clogging of the porosity, it has been decided to focus on the mechanical effects of the salt crystallization and the possible deformation of the host rock. A macroscopic and microscopic modelling has then been developed, taking into account two possible modes of evaporation induced by the spatial distribution of residual water, in order to predict the behavior of a porous material subjected to the drying by carbon dioxide injection. Results show that crystallization pressure created by the growth of a crystal in a confined medium can reach values susceptible to locally exceed the mechanic resistance of the host rock, highlighting the importance of these phenomena in the global mechanical behavior of the aquifer. At the experimental level, the study of a rock core submitted to the injection of supercritical carbon dioxide has been proceeded on a new reactive percolation prototype in order to obtain the evolution of permeabilities in conditions similar to these of a deep saline aquifer.