Investigating the role of water on CO2-Utica Shale interactions for carbon storage and shale gas extraction activities - Evidence for pore scale alterations

In this work, we probed the physical and chemical alteration of the carbonate-rich Utica Shale following CO2 exposure when thin films of water were present at the shale surface. All reaction conditions were examined at 40 degrees C and CO2 pressures up to 10.3 MPa for 14 days. CO2 dissolution in the water layer at 2342 cm(-1) and carbonate dissolution and precipitation at 1424, 874, and 712 cm(-1) were discerned with in-situ Fourier Transform infrared spectroscopy (FT-IR). Significant etching and pitting from exposure to CO2 and water were observed with feature relocation scanning electron microscopy (SEM). Application of the density function theory (DFT) for pore size analysis showed that micropores between approximately 0.9 and 2 nm disappeared while the mesopore volume increased after dissolution of carbonate. These results may provide new insights that carbonate rich shales such as the Utica may have a greater potential for alterations of pore space due to the reactivity of CO2 which may affect 1) how CO2 storage in shale formations plays a role in Carbon Capture and Storage (CCS) activities, 2) if CO2 can be utilized as a potential fracturing agent, and 3) whether CO2 is an effective fluid for enhanced hydrocarbon extraction.