CHARACTERIZATION OF THE CO2-FLUID-SHALE INTERFACE VIA FEATURE RELOCATION USING FIELD-EMISSION SCANNING ELECTRON MICROSCOPY AND IN SITU INFRARED SPECTROSCOPY

Shale is unique in that it can serve as either a CO₂ sealing or a CO₂ storage formation. Low permeability, unfractured, shale intervals can act as sealing layers, ensuring vertical containment of geologic storage of CO₂. Fractured, organic rich shales, have been shown to be both the source rock and a trap of unconventional gas and oil. Research is underway evaluating the role that shale intervals may play as targets for the storage of anthropogenic CO₂.

Hydraulic fracturing fluids and CO₂ interactions with shales can influence the properties of the rock by such mechanisms as chemical alteration, matrix swelling/shrinkage, and related geomechanical effects. As such, it is important to understand the influence that hydraulic fracturing fluid-CO₂-shale interactions may have on shale mechanical and hydrodynamic properties, and how these interactions vary in different shales.

Experiments include in situ fracturing fluid-rock and SCCO2-rock interaction studies. Shale samples were examined before and after in situ exposure using surface relocation techniques via high-resolution field-emission scanning electron microscopy (FE-SEM) to investigate chemical or physical alterations. This study also targets CO₂ storage in shale formations and focuses on characterizing the interface between the injected CO₂ and shale with in-situ infrared spectroscopy. Precipitates such as gypsum, barite, strontanite, celestine, and apatite as well as carbonate dissolution and fracture propogation were observed under varying conditions. Results indicate a complex precipitation/dissolution in response to local changes in Eh and pH.