Center for Nanoscale Control of Geologic CO 2 Structure and Dynamics of CO 2 -bearing Fluids at Nanoscale Interfaces

SUMMARY Injection of CO 2 into geologic formations has been identified as a key strategy for mitigating the impact of anthropogenic emissions of CO 2 . A key aspect of this process is the prevention of leakage from the host formation by an effective cap or seal rock which has low porosity and permeability characteristics. Shales comprise the majority of cap rocks encountered in subsurface injection sites with pore sizes typically less than 100 nm and surface chemistries dominated by quartz (SiO 2 ) and clays. We still lack a fundamental understanding of the structural and dynamic behavior of CO 2 (and CO 2 -bearing aqueous fluids) in cap rock environments dominated by nanoporosity for state conditions encountered in injection systems. Even for a simple fluid such as CO 2 we have not adequately explored interfacial phenomena such as the wetting and adsorption for variable pore sizes, pore geometries and pore wall chemistry at conditions approaching and crossing into the supercritical regime. Using a combination of electron microscopy, neutron scattering and molecular simulations we have addressed five interrelated issues: (i) the nature of nanoporosity in shales, (ii) key experimental results on CO 2 matrix interactions relevant to sequestration, (iii) a MD assessment of adsorption behavior of gaseous and supercritical CO 2 interacting with a SiO 2 substrate, (iv) MD modeling of the microscopic behavior of CO 2 -H 2 O at SiO 2 surfaces and (v) a new MD description of CO 2 in slit pores (muscovite). Key results are presented here on some of these issues.