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.