## 3 Gas Desorption Laws of Coal with Different Water-Bearing States under Various Stress Paths
### Influencing Analysis of Stress on Gas Desorption and Emission from Water-Bearing Coal Samples  
As a heterogeneous porous solid medium, coal can be characterized as a solid particle skeleton structure, and the forced compression of coal can be regarded as the combination of pore volume reduction and solid particle skeleton volume reduction [23]. The high-pressure fluid presplitting and permeability enhancement process is adopted for deep coal. In addition to ground stress, coal is also affected by the change in the high-pressure fluid stress, which directly influences the gas occurrence in coal and the gas desorption and emission.  
Through the above tests, it can be observed that the stress promoted the gas desorption of water-bearing coal, and the total accumulated gas desorption observed in water-bearing coal also increased under various stress paths when the stress grew. The influence of gas desorption and emission could be further analyzed as follows:  
1. There is a multi-stage pore system in the coal body, in which micro-pores filled with gas are characterized as \"a gas storage molecular system\", representing a strong gas adsorption zone; under the stress action, the particle skeleton structure and the pore volume of coal are compressed, the gas adsorption equilibrium is destroyed, and a large amount of free gas is desorbed by the pore diffusion system, representing a weak gas adsorption zone; a connective channel exists between the pore system and the seepage system, and the compressed gas molecules are quickly discharged, which leads to the increase in the total accumulated gas desorption from coal.
2. The test coal is anthracite, which has a high degree of micropore development, and the larger the specific surface area of coal, the greater the gas adsorption capacity [24; 25]. The coal is infiltrated by high-pressure fluid stress, which results in the competitive adsorption and desorption of water and gas molecules in the pore diffusion system in the weak pore adsorption zone. Under the high-pressure fluid stress, however, the gas desorption capacity is weakened, a large number of water molecules infiltrate the pore diffusion system to displace gas molecules in a specific stage, and water  
Figure 6: Variation of limiting desorption amount provided by coal samples with a moisture content of 3.24% under various stress path states.  
molecules block the connective channel between the pore diffusion system and the seepage system, resulting in the difference in gas emission in this zone.
3. The stress on coal reduces the connective channel between the pore diffusion system and the seepage system, and changes the gas occurrence and gas migration resistance, as shown in Figure 7 (water molecules are blue, gas molecules are colorless). Pore channel A of the water-bearing coal is the channel size before the stress is applied (solid line part), and A\({}_{1}\) and A\({}_{2}\) are the channel sizes after the stress is applied (dotted line part). Due to the blockage of water molecules and the narrowing of gas migration channels, the pore pressure increases, which increases the pressure difference between gas channels.