Mechanical properties of sandstone under in-situ high-temperature and confinement conditions

• In-situ high-temperature triaxial tests reveal that sandstone peak stress decreases with temperature but increases with confining pressure, with the confining pressure effect diminishing at higher temperatures. • Thermal conductivity and diffusivity of sandstone show a linear relationship with temperature, while mass loss increases with temperature. • Poisson's ratio and internal friction angle decrease with rising temperature, with 400°C identified as a threshold for friction angle reduction. • Under confining pressures of 10 and 20 MPa, damage stress decreases with temperature, whereas uniaxial damage stress is less temperature-sensitive, providing critical data for caprock integrity in oil shale conversion.