The effects of long-term supercritical CO₂ exposure on Zululand Basin core samples

Carbon dioxide (CO₂) sequestration in geological formations is a viable solution for ensuring coal-based energy supply whilst reducing CO₂ emissions. The variation in the microstructure and composition of geological formations before and after CO₂ storage plays a significant role in CO₂ sequestration. Three core samples obtained from the Zululand Basin in South Africa were exposed to supercritical CO₂ (ScCO₂) in the presence of water under typical hydrothermal conditions (175 bar, 70 °C) for up to 2 months. The samples were characterized pre- and post-treatment using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), low pressure nitrogen (N₂) adsorption and low pressure CO₂ adsorption. Physical and chemical structural changes were observed in all three samples after treatment, to varying degrees. Mineral alterations were observed in the three samples, including plagioclase and calcite dissolution/precipitation and quartz composition changes. Dissolution of organic components and surface chemistry alterations were found in two of the core samples. Increases in pore volume, surface area and CO₂ adsorption capacity were observed in all studied samples after CO₂ treatment.