Simulation study on temperature field expansion of surrounding rock in underground coal gasification considering coupling effect of high temperature-thermal parameters

The high temperature produced in the process of underground coal gasification changes the thermal parameters of the surrounding rock in the goaf,thus affecting the propagation of the temperature field of the surrounding rock in the goaf. At present,there is a lack of research on the temperature field expansion law of surrounding rock in underground coal gasification under the coupling effect of high temperature-thermal parameters,which causes the inversion calculation of temperature field expansion in gasification process to be relatively distorted,and limits the development of surrounding rock control technology in underground coal gasification stope under the condition of multi-field coupling. In this paper,Fish language is used to improve the heat conduction model of FLAC3D,the numerical simulation method of temperature field research under the coupling effect of high temperature and thermal parameters is established,and it is applied to the study of temperature field expansion of surrounding rock in underground coal gasification,and the following results are obtained. High temperature has greatly changed the distribution of thermal parameters of coal,at the same time,the distribution of thermal parameters has also changed the expansion law of temperature field. High temperature and thermal parameters have bidirectional coupling characteristics. The expansion of surrounding rock temperature field in underground coal gasification has experienced three stages,namely,the high temperature expansion stage in the process of coal seam combustion,the cooling expansion stage in the process of convection heat dissipation,and the stable expansion stage without heat exchange with the outside world after gasification. The coupling effect of thermal parameters changed the distribution of temperature field in underground surrounding rock of coal. After the high temperature expansion stage,the temperature field spread in the roof was 3.2 m,the coal walls on both sides were 6.5 m,and the floor was 1.3 m. During the cooling expansion stage,the temperature field spread in the roof is 12.2 m,the coal walls on both sides are 7 m,and the floor is 5.5 m. After gasification,the temperature field continuously propagates in the surrounding rock of the goaf,which continues to affect the long-term stability of the surrounding rock of the goaf.