Abstract: In order to study the effect of supercritical carbon dioxide (ScCO2) on the mechanical properties of granite located in and near the core of the CO2-based enhanced geothermal system (EGS) region, fluid–rock interaction experiments were conducted at 210, 240 and 270 ℃. Three test conditions were used: (1) ScCO2 and dry granite; (2) ScCO2, water vapor and granite; and (3) ScCO2 and granite soaked in water for 24 h. The P-wave velocity, uniaxial compressive strength (UCS), and Young’s modulus of all ScCO2- treated granite samples and one untreated granite sample were obtained by carrying out the wave velocity tests and uniaxial compression tests. The wave velocity tests showed that the P-wave velocities of all ScCO2-treated granite samples were reduced compared to that of the untreated sample. The uniaxial compression test showed that the UCS and Young’s modulus were almost not affected. From the failure mode, it can be seen that the untreated granite more likely presented the brittle tensile failure, while the treated sample showed more likely shear failure. As the temperature increased, the failure mode became more and more close to shear failure. Experimental results showed that the ScCO2 induced slight damage to the granite under dry or a little water condition, causing a slight decrease in the brittleness, and a small increase in the plasticity. The P-wave velocity decreased slightly and the impact on the granite strength can be negligible. Therefore, the interaction of CO2–rock will not cause obvious effect on the mechanical properties of granite located in and near the core of the CO2–EGS region.

Key words: CO2, enhanced geothermal system (EGS), granite, high temperature and high pressure, mechanical property