Synergistic Coupling of CO and HO during Expansion of Clays in Supercritical CO-CH Fluid Mixtures.

We used IR and XRD, with supporting theoretical calculations, to investigate the swelling behavior of Na-, NH-, and Cs-montmorillonites (SWy-2) in supercritical fluid mixtures of HO, CO, and CH. Building on our prior work with Na-clay that demonstrated that HO facilitated CO intercalation at relatively low RH, here we show that increasing CO/CH ratios promote HO intercalation and swelling of the Na-clay at progressively lower RH. In contrast to the Na-clay, CO intercalated and expanded the Cs-clay even in the absence of HO, while increasing fluid CO/CH ratios inhibited HO intercalation. The NH-clay displayed intermediate behavior. By comparing changes in the HOH bending vibration of HO intercalated in the Cs-, NH-, and Na-clays, we posit that CO facilitated expansion of the Na-clay by participating in outer-sphere solvation of Na and by disrupting the H-bond network of intercalated HO. In no case did the pure CH fluid induce expansion. Our experimental data can benchmark modeling studies aimed at predicting clay expansion in humidified fluids with varying ratios of CO and CH in real reservoir systems with implications for enhanced hydrocarbon recovery and CO storage in subsurface environments.