For environmentally sustainable subsurface operations related to geologic CO2 sequestration (GCS), unconventional gas and oil resources, and disposal of nuclear waste, a better understanding of the effects of illite formation on the fate and transport of injected fluids during these operations is needed. In this study, we conducted experiments to study mica dissolution, surface morphological changes, and secondary mineral precipitation under saline hydrothermal conditions. Batch dissolution experiments were conducted with biotite and phlogopite under conditions relevant to GCS sites (55�95�C, 1 M NaCl, and 102 atm CO2) in the absence and presence of simple carboxylic compounds. In these salt solutions, numerous illite fibers precipitated after reaction for only 3 h at 95�C. Interestingly, when dissolution is slow, slow illite precipitation processes caused oriented aggregation of hexagonal illite nanoparticles forming the fibrous illite. This observation suggests new possible mechanisms for fibrous illite formation. Precipitation of fibrous illite in shale/sandstone pores has attracted much interest because illite fibers can significantly lower permeability in porous media and cause serious problems for hydrocarbon production. Although experiments were conducted under GCS conditions, the improved understanding can be applicable for other subsurface projects, such as unconventional gas and oil resources and disposal of nuclear waste.

Nanogeochemistry of illite in shale pores

247th National Meeting (2014)

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