Shale pore alteration: Potential implications for hydrocarbon extraction and CO2 storage

Shale unconventional reservoirs are currently and expected to remain substantial fossil fuel resources in the future. As CO2 is being considered to enhance oil recovery and for storage purposes in unconventional reservoirs, it is unclear how the shale matrix and fractures will react with CO2 and water during these efforts. Here, we examined the Utica Shale and its reactivity with CO2 and water using scanning electron microscopy, N2 and CO2 sorption isotherms, mercury intrusion porosimetry, and X-ray scattering methods. During CO2 exposure, the presence of water can inhibit CO2 migration into the shale matrix, promote carbonate dissolution, and dramatically change the pore scale variability by opening and closing pore networks over the macro- to nano-scale range. These alterations in the shale matrix could impact flow pathways and ultimately, oil recovery factors and carbon storage potential.