Abstract: In the process of CO2 geological storage, the mechanical stability of rock can be influenced by changes in the composition and pressure of pore fluid due to CO2 injection into deep rock stratum. In addition, adverse consequences may further arise, such as reservoir caprock rupture, surface uplifting, and small and medium scale earthquakes. The triaxial compression tests of rock were conducted to compare the effects of pore fluid media of supercritical CO2, N2 and H2O under single-phase fluid. The fluid temperature and pore fluid pressure were controlled and adjusted to analyse the strength, elastic modulus and Poisson's ratio under single-phase fluid coupling. It was found that the peak strength and elastic modulus of dry sandstone were reduced at various degrees by high-pressure pore fluid. However, Poisson’s ratio increased obviously, and the impacts of pore fluid were H2O, CO2 and N2 in the descending order. The pore fluid decreased the brittleness of dried yellow sandstone and enhanced plastic deformation to a certain degree. Besides, the water-bearing sandstone had the strongest plastic property. The effect of pore fluid on mechanical properties of sandstone depended on the strength of interaction between the fluid and mineral composition of rock. The selective absorption of CO2, N2 and H2O by different mineral compositions of sandstone resulted in a significant difference in the effect of pore fluid on sandstone strength. The action effects ranked as H2O, CO2 and N2 in the ascending order.

Key words: CO2 geological storage, single-phase, ture triaxial test, strength properties, sandstone