Supercritical fluid behavior at nanoscale interfaces: Implications for CO₂ sequestration in geologic formations

We report the behavior of pure CO₂ interacting with simple substrates, i.e. SiO₂ and muscovite, that act as proxies for more complex mineralogical systems found in shale cap rocks. Modeling of small-angle neutron scattering (SANS) data taken from CO₂- silica aerogel (95% porosity; 6 nm pores) interactions indicates the presence of fluid depletion for conditions above the critical density. A theoretical framework, i.e. integral equation approximation (IEA), is presented that describes the fundamental behavior of near-critical adsorption onto a non-confining substrate that is consistent with SANS experimental results. Structural and dynamic behavior for supercritical CO₂ interaction with muscovite (KAl₂Si₃AlO₁₀(OH)₂) was assessed by classical molecular dynamics (CMD). These results indicate the development of distinct layers of CO₂ within slit pores, reduced mobility by one to two orders of magnitudes compared to bulk CO₂ depending on pore size and formation of bonds between CO₂ oxygens and H from muscovite hydroxyls.