Study on the Spatiotemporal Evolution Characteristics of Gas Pressure Field during Gas Injection into Loaded Coal

To investigate the spatiotemporal distribution characteristics of gas pressure inside coal during gas injection, this study utilized N₂ and CO₂ as the injection source gases. By combination of experimental research with theoretical analysis, the internal gas pressure variation in coal during the injection process was analyzed in-depth. The differences in gas pressure between the two source gases were compared, and the influence of strong-adsorption and weak-adsorption gases on the internal gas pressure was explored. The results show that the distribution of the gas pressure within the coal during injection is not uniform. Under a constant injection pressure of 0.7 MPa, the maximum pressure difference is approximately 0.17 MPa. The internal gas pressure exhibited distinct variation characteristics during N₂ and CO₂ injection. Due to the weaker adsorption of N₂, it mainly exists in a free state after entering the coal. Thus, the internal gas pressure in the coal rises rapidly at the early stage of injection but then gradually decreases as some N₂ exits the outlet. Conversely, CO₂ quickly transitions to an adsorbed state after entering the coal, leaving little free gas in the coal. Combined with the outflow of some gas from the outlet, the internal gas pressure initially shows a downward trend during the early stage of CO₂ injection. Later, as CO₂ gradually reaches adsorption saturation, the gas pressure begins to increase slowly. These findings provide a basis for selecting optimal injection source gases and offer a reference for addressing safety issues during the gas injection process.