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

Abstract

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.