Experimental study on the fissure structure and permeability evolution characteristics of coal under liquid nitrogen freezing and freeze–thaw

Liquid nitrogen (LN 2 ) fracturing technology as a kind of waterless has received extensive attention in recent years. In order to investigate the evolution law fissure structure and seepage characteristics coal samples under LN freezing freeze–thaw, before after freeze–thaw was monitored by micro-computed tomography, change permeability different time cycles measured, damage mechanism discussed. The experimental results show that (1) can cause shrinkage matrix, resulting sample, which promotes initiation, expansion, extension sample form new and, finally, forms fracture network. (2) increment increase with number gas pressure confining condition. (3) Under same time, growth rate condition is significantly greater than (4) frost-heave force thermal stress are main factors leading damage, promoting formation increasing freeze–thaw. This study provides theoretical basis for understanding .