## 3 Experimental Results and Analysis
### \(T_{1}\)-\(T_{2}\) Spectrum Test Results  
Longitudinal relaxation T\({}_{1}\) can reduce the total energy of the magnetic nucleus, and transverse relaxation T\({}_{2}\) does not decrease the total energy of magnetic nucleus. There was a linear relationship between the pore size characterization and the two relaxation times. The two relaxation times jointly represent the size of the internal pore diameter of the coal sample. The longer the two relaxation times are, the larger the pore diameter is, and the smaller the pore diameter is. Similarly, the distribution range of the two relaxation times represents the size of the aperture, and the larger the distribution range is, the larger the aperture is. The distribution region of pore size of coal sample can be obtained by combining the distribution of two kinds of relaxation time. When the two relaxation times are within the range of [0.01, 1] at the same time, it represents the distribution of small-size pores. When the two relaxation times are in the range of [1, 100] and [100, 10,000] at the same time, they represent the distribution of medium pores and large pores, respectively. Figure 4 shows the T\({}_{1}\)-T\({}_{2}\) spectra of coal samples at different melting temperatures. When the temperature was \(-\)196 \({}^{\circ}\)C, the longitudinal and transverse relaxation times of coal samples were within the range [0.001, 1], and the pores were mainly dominated by bound water. When the melting temperature reached \(-\)20 \({}^{\circ}\)C, part of the frozen water began to melt, starting from the small pore. When coal samples melted from \(-\)2 \({}^{\circ}\)C to 10 \({}^{\circ}\)C, both longitudinal and transverse relaxation time was in the [0.1, 100] range, large pores in the ice began to melt and not frozen water content increased gradually. However, the bound water distribution was significantly reduced; this is the reason why there ice pores at lower temperatures, not frozen in ice pore water, were detected as bound water. This is consistent with the phenomenon of the first peak \"rightward shift\" in the T\({}_{2}\) spectrum above. Figure 5 shows the distribution range of relaxation time of coal samples at non-melting temperature. At \(-\)196 \({}^{\circ}\)C and \(-\)20 \({}^{\circ}\)C, the transverse relaxation of coal samples had a similar interval width, but the transverse relaxation from \(-\)196 \({}^{\circ}\)C was mainly distributedin a short time, and the transverse relaxation from \(-20\)\({}^{\circ}\)C was concentrated in a relatively long time interval. In addition, in the melting process from \(-2\)\({}^{\circ}\)C to \(10\)\({}^{\circ}\)C, the two relaxation signals of coal samples were mainly concentrated in the medium and long time interval. For the longitudinal relaxation distribution of coal samples at non-melting temperature, at \(-196\)\({}^{\circ}\)C, the longitudinal relaxation signal of coal samples was mainly distributed in a short interval, while the coal samples from \(-20\)\({}^{\circ}\)C to \(10\)\({}^{\circ}\)C showed a similar interval distribution, mainly distributed in a short and medium interval. However, the distribution range of coal samples in the direction of longitudinal relaxation signal at the four temperatures was very different, and the coal samples from \(-20\)\({}^{\circ}\)C to \(10\)\({}^{\circ}\)C always had the largest interval range. In two-dimensional T\({}_{1}\)-T\({}_{2}\) spectra, the integral areas of different regions represent the specific generational values of different fluid storage spaces. Figure 6 shows the distribution space of unfrozen water in coal samples at different melting temperatures. As can be seen from Figure 6, when the temperature ranged from \(-196\)\({}^{\circ}\)C to \(-20\)\({}^{\circ}\)C, the spatial growth slope of unfrozen water distribution was small, and unfrozen water concentrated in a small range.