Temperature evolution law and strain characteristics of rapid freeze-thaw coal impacted by liquid CO2 -high temperature steam cycles

In view of the fact that the natural melting time of frozen coal is too long in the process of low temperature pneumatic antireflection, and the migration path of unconventional oil and gas is blocked by porous ice. A rapid freeze-thaw antireflection technique for coal seams using liquid CO2 and high temperature water vapor as the medium is proposed. The results show that high temperature steam can significantly promote the melting of liquid CO2 frozen coal. The coal strain changes suddenly when the temperature changes suddenly, and the strain decreases continuously with the temperature conduction becoming stable. With the increase of the number of cold and hot cycle impacts, the time of a single cycle increases first and then decreases. As the degree of metamorphism increases, the strain of coal decreases, and the strain of lignite is 2.71 times that of anthracite. After 6 times of cold and hot cycle impact, the lignite is broken, and the bituminite and anthracite appear macroscopic cracks. In the process of temperature shock, the coal produces residual strain, which first increases and then decreases with the increase of the number of cold and hot cycles.