Abstract: In order to study the effect of supercritical carbon dioxide (ScCO2) on the mechanical properties of granite located in the CO2 based enhanced geothermal system (EGS) region, fluid-rock interaction experiments were conducted at 210 ℃, 240 ℃ and 270 ℃. Three experimental conditions were used: i) ScCO2 and dry granite; ii) ScCO2, water vapor and dry granite; iii) ScCO2 and granite that is soaked in water for 24 hours. The P-wave velocities, uniaxial comprehensive strength, and elastic modulus of all these ScCO2 treated granite samples and one untreated granite sample were obtained by carrying out the wave velocity tests and uniaxial compressive tests. Wave velocity tests show that the P-wave velocities of all these ScCO2 treated granite samples are reduced compared to that of the untreated sample. Uniaxial compressive test show that the uniaxial comprehensive strength and elastic modulus are not affected. From the failure mode, it can be seen that the untreated granite more likely present brittle tensile failure, while the treated sample shows more likely shear failure. As the temperature increases, the failure mode becomes more and more close to shear failure. Experimental results show that the ScCO2 has very slight damage impact on granite that has no water or little water, causing a slight decrease in the brittleness, and a small increase on the plasticity. The P-wave velocity decreases slightly and the damage to 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 nearby the CO2-EGS region.

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