In Situ 13C and 23Na Magic Angle Spinning NMR Investigation of Supercritical CO2 Incorporation in Smectite–Natural Organic Matter Composites

Abstract

This Article presents an in situ NMR study of clay–natural organic polymer systems (a hectorite–humic acid [HA] composite) under CO2 storage reservoir conditions (90 bar CO2 pressure, 50 °C). The 13C and 23Na NMR data show that supercritical CO2 interacts more strongly with the composite than with the base clay and does not react to form other C-containing species over several days at elevated CO2. With and without organic matter, the data suggest that CO2 enters the interlayer space of Na–hectorite equilibrated at 43% relative humidity. The presence of supercritical CO2 also leads to increased 23Na signal intensity, reduced line width at half height, increased basal width, more rapid 23Na T1 relaxation rates, and a shift to more positive resonance frequencies. Larger changes are observed for the hectorite–HA composite than for the base clay. In light of recently reported MD simulations of other polymer–Na–smectite composites, we interpret the observed changes to be due to an increase in the rate of Na+ s...