Abstract:

Sandstone is a crucial rock type for CO₂ aquifer storage. The clay minerals within it expand upon adsorbing CO₂ or H₂O, which affects the rock’s mechanical properties and may threaten the reservoir’s mechanical stability. A type of quartz-cemented sandstone with low clay content was studied. Triaxial compression experiments were performed under dry, H₂O, and supercritical CO₂ (scCO₂) saturation conditions, maintaining a constant pore pressure of 10 MPa. The effects of various fluids on the peak strength, cohesion, friction angle, and both macroscopic and microscopic failure characteristics of sandstone were compared and analyzed. Results indicated that, compared to dry conditions, scCO₂ and H₂O presence significantly reduced the peak strength of sandstone samples by 7.61% and 18.02%, respectively. Under different confining pressure levels, the weakening effect of scCO₂ on sandstone peak strength remained nearly constant, whereas the weakening effect of H₂O first increased and then decreased with rising confining pressure. The cohesion of sandstone decreased by 12.11% and 16.03% under scCO₂ and H₂O saturation, respectively, while the friction angle was remained nearly unaffected by the fluids. Both scCO₂ and H₂O reduce the failure angle of sandstone.

Key words: CO₂ geological storage, sandstone, clay mineral, triaxial compression, mechanical property