Abstract
The analysis of species behavior involving dilute fluid environments has been
crucial for the advance of modern solvation thermodynamics through molecular-based
formalisms to guide the development of macroscopic regression tools in the description
of fluid behavior and correlation of experimental data (Chialvo 2013). Dilute fluid
environments involving geologic formations are of great theoretical and practical
relevance regardless of the thermodynamic state conditions. The most challenging
systems are those involving highly compressible and reactive confined environments, i.e.,
where small perturbations of pressure and/or temperature can trigger considerable density
changes. This in turn can alter significantly the species solvation, their preferential solvation, and consequently, their reactivity with one another and with the surrounding
mineral surfaces whose outcome is the modification of the substrate porosity and
permeability, and ultimately, the integrity of the mineral substrates. Considering that
changes in porosity and permeability resulting from dissolution and precipitation
phenomena in confined environments are at the core of the aqueous CO2-mineral
interactions, and that caprock integrity (e.g., sealing capacity) depends on these key
parameters, it is imperative to gain fundamental understanding of the mineral-fluid
interfacial phenomena and fluid-fluid equilibria under mineral confinement at subsurface
conditions. In order to undertand the potential effects of acid gases as contaminants of
supercritical CO2 streams, in the next section we will discuss the thermodynamic
behavior of CO2 fluid systems by addressing two crucial issues in the context of carbon
capture, utilization and sequestration (CCUS) technologies: (i) Why should we consider
(acid gas) CO2 impurities? and (ii) Why are CO2 fluid - mineral interactions of
paramount relevance?