Pore characteristics and permeability changes of high-temperature sandstone after rapid dry ice cooling

The temperature of dry ice is very low, about -78.5 & DEG;C. When it contacts with high-temperature rock, it will cause some damage to the rock. This paper takes sandstone as the research object; dry ice is used to rapidly cool the rock after high-temperature treatment at different temperatures (25-800 & DEG;C). The pore fracture development and permeability changes are measured by nuclear magnetic resonance (NMR) technology, and the following conclusions are obtained: (1) cracks appear on the surface of the sample after treatment at 500 & DEG;C, when the temperature reaches 600 & DEG;C, the number of internal micropores (0 ms < T-2 < 10 ms) increases significantly; (2) the thermal expansion of calcite, the phase transformation of quartz, and the thermal stress impact effect under extreme temperature difference after dry ice cooling are the main reasons for the change of permeability; (3) the rapid cooling of ultra-low-temperature dry ice intensifies the thermal damage of sandstone. Compared with natural cooling, dry ice cooling improves the porosity and permeability of sandstone more significantly.