Study of thermal-mechanical coupling numerical simulation of similar simulation experiment of underground coal gasification

In order to study the distribution and evolution of temperature,stress and displacement fields of coal and rock layers under thermo-mechanical coupling conditions during underground coal gasification (UCG),the thermo-mechanical coupling research of UCG simulation experiments in experimental furnaces were carried out by COMSOL software.The simulation based on a simplified model of the burning area expansion,the process of expanding the burning area of a section perpendicular to the gasification channel into two stages of heating and cooling.By fitting the boundary temperature rise curve of the burning area and adopting the physical parameters variable setting with temperature as the independent variable,a reasonable thermo-coupling study is carried out to obtain distribution of the temperature field,the first principal stress field and the vertical displacement field which are closer to the real situation.The distribution law of temperature field,the first principal stress field and vertical displacement field is studied by the COMSOL time-dependent model.The results show that since the ignition point is located at the bottom of the coal seam,the heat transfer has little effect on the roof after ignition until the burning area is extended to half of the maximum extension radius.The heat is mainly transmitted in the coal seam and the direct bottom,and the range is gradually expanded.During this time,the movement of the combustion boundary of the burning area is the main reason for the high temperature of the coal seam and the direct bottom part; in the process of the expansion of the burning area,the first main strain is mainly generated in the vicinity of the burning area,mainly concentrated in the coal seam and the bottom plate.After the burning area is extended to half of the maximum extension radius,the area of the coal-rock layer affected by the main strain does not change much,but in this zone,the value of the main strain of the vicinity of the arc-shaped boundary of the burning area continues to increase; during the warming phase,the rock mass is thermally expanded,and the vertical displacement is generally upward,and the value increases from bottom to top in the model,and decreases from the inside to the outside.The simulation results are helpful to study the damage of UCG to surrounding rocks from the perspective of thermosetting coupling.