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Open Access Publications from the University of California

Supercritical CO2uptake by nonswelling phyllosilicates

  • Author(s): Wan, J
  • Tokunaga, TK
  • Ashby, PD
  • Kim, Y
  • Voltolini, M
  • Gilbert, B
  • DePaolo, DJ
  • et al.

Interactions between supercritical (sc) CO2and minerals are important when CO2is injected into geologic formations for storage and as working fluids for enhanced oil recovery, hydraulic fracturing, and geothermal energy extraction. It has previously been shown that at the elevated pressures and temperatures of the deep subsurface, scCO2alters smectites (typical swelling phyllosilicates). However, less is known about the effects of scCO2on nonswelling phyllosilicates (illite and muscovite), despite the fact that the latter are the dominant clay minerals in deep subsurface shales and mudstones. Our studies conducted by using single crystals, combining reaction (incubation with scCO2), visualization [atomic force microscopy (AFM)], and quantifications (AFM, X-ray photoelectron spectroscopy, X-ray diffraction, and off-gassing measurements) revealed unexpectedly high CO2uptake that far exceeded its macroscopic surface area. Results from different methods collectively suggest that CO2partially entered the muscovite interlayers, although the pathways remain to be determined. We hypothesize that preferential dissolution at weaker surface defects and frayed edges allows CO2to enter the interlayers under elevated pressure and temperature, rather than by diffusing solely from edges deeply into interlayers. This unexpected uptake of CO2, can increase CO2storage capacity by up to ∼30% relative to the capacity associated with residual trapping in a 0.2-porosity sandstone reservoir containing up to 18 mass % of illite/muscovite. This excess CO2uptake constitutes a previously unrecognized potential trapping mechanism.

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