Experimental study on the mechanical properties of sandstone under different temperatures and cooling methods

To explore the damage mechanism of sandstone mechanical properties under the coupling effect of high temperature and water cooling during the geothermal exploitation of hot dry rock, this paper conducts comparative experiments of natural cooling and water cooling on sandstone treated at 200-600 degrees C, and combines uniaxial compression mechanical tests with microscopic morphology analysis to systematically reveal the macroscopic and microscopic damage evolution laws of sandstone under the combined effect of temperature and cooling. The research shows that with the increase of temperature, the peak stress and elastic modulus of sandstone show a phased decline, and 400 degrees C is the threshold temperature for the sudden change of mechanical properties. Water cooling aggravates thermal damage compared with natural cooling. At 600 degrees C, the peak stress reduction of watercooled samples is 1.8 times that of naturally cooled samples, and the volume expansion rate increases by 37 %. Microscopic analysis indicates that water cooling induces thermal mismatch stress between mineral particles, which leads to a more significant increase in the proportion of transgranular cracks at 600 degrees C. The established polynomial model can accurately characterize the temperature dependence of mechanical parameters. The research results provide a theoretical basis for the regulation of thermal fracturing in hot dry rock reservoirs and the assessment of wellbore stability.