Research on the Effect of Freeze–Thaw Cycles at Different Temperatures on the Pore Structure of Water-Saturated Coal Samples

[Image: see text] To study the pore structure transformation of coal at different temperatures, freeze–thaw cycle experiments at different temperature intervals (20 to −20 °C, 20 to −40 °C, 20 to −196 °C) were carried out. The low-field nuclear magnetic resonance equipment was used to characterize the peak area, pore size distribution, and pore number of each group of coal samples. The pore transformation effect of coal samples at different temperature intervals was compared, and the change characteristics of the pore structure of coal samples under the freeze–thaw action were explored. The research shows that the freeze–thaw cycles at different freezing temperature intervals have obvious differences in the effect of coal pore transformation. The area of each peak spectrum in the T(2) distribution curve of coal samples increased significantly under the action of freeze–thaw cycles in different freezing temperature intervals. The increased value of the number of mesopores and macropores shows the phenomenon of “first increase and then decrease” with the increase of the temperature difference. There is a quadratic function relationship between the temperature difference in the freezing temperature interval and the proportion change rate of the adsorption pore or seepage pore. The continuous increase of the temperature difference has a certain marginal effect on the proportion change rate of seepage pores and adsorption pores in coal.