Fracture and mechanical characteristics of CO₂-saturated sandstone at extreme loading conditions

Dynamic compression and Brazilian disc tests were performed on dry, water- and brine-saturated sandstone with and without scCO ₂ (supercritical carbon dioxide) injection. Split Hopkinson pressure bar (SHPB) tests were conducted under different strain rates. The full-field deformation and fracturing process were investigated by the high-speed 3D digital image correlation (DIC) technique with a resolution of 256 × 256 pixels at 200,000 frames per second (fps). The presence of CO ₂ attenuated the dynamic compressive strength for dry and water-saturated sandstone. The dry sandstone has a greater brittleness with the saturation of CO ₂ , but there was an opposite trend for water-saturated sandstone saturated by CO ₂ . The presence of CO ₂ had less effect on the dynamic mechanical properties on the brine-saturated sandstone. The normalised stress threshold for crack initiation became lower for the dry and water treated specimen but was less effective in brine-saturated sandstone. The injection of CO ₂ intensified the fracturing degree, branching and altered the crack initiation position under dynamic loading. The mechanism of CO ₂ effect was studied from mineralogical structure alteration based on the observation by scanning electron microscope (SEM).