Dynamic response characteristics and coupling law of multi physical field parameters in coal seam gas drainage

To further deepen the understanding of the dynamic response characteristics and coupling mechanism of multi field parameters during coal mine gas drainage, the self-developed multi field coupling gas drainage physical simulation test device was used to carry out the physical simulation test of gas synchronous drainage in different stress areas in front of the working face. The real-time evolution characteristics of coal temperature field, gas pressure field and coal deformation field and the coupling mechanism of multiple physical fields were analyzed. The results show that:(1) During the synchronous drainage, the decreasing rate of coal temperature in stress zone Ⅳ is the fastest, followed by those in stress zone I and stress zone Ⅱ. the decreasing rate of temperature in stress zone Ⅲ is the slowest. The attenuation characteristics of gas pressure in different regions are similar to the law of coal temperature decline. The coal deformation is affected by the coupling effect of coal temperature and gas pressure, which makes the coal deformation increases nonlinearly. The coal deformation in stress zone Ⅳ is the largest, and the coal deformation in stress zone Ⅲ is greater than that in stress zone I and stress zone Ⅱ due to the limitation of poisson effect.(2) During synchronous drainage, the coal deformation in each stress area has the characteristics of phased change which is divided into deformation delay stage, deformation start-up stage and deformation secondary increasing stage. The essence of deformation delay is the binding effect of a large number of micropores and pores in the coal seam on the desorption of adsorbed gas, coupled with the capillary condensation effect of coal matrix on gas, resulting in the lag of gas desorption, thus, the coal deformation is delayed. With the progress of drainage, the coal deformation delay is broken through, the deformation increases gradually, and the phenomenon of secondary increase appears.(3) The dynamic response of coal deformation in each stress region is affected by effective stress compression effect, matrix shrinkage effect, desorption heat shrinkage effect and poisson effect. poisson effect plays a leading role in stress zone Ⅲ. effective stress compression effect is the key factor to break through the deformation delay phenomenon. desorption heat shrinkage effect and matrix shrinkage effect are the main reasons for the secondary increase of coal deformation.