Research on Factors and Influencing Correlation of Coal Core Temperature during Coring

The core-tube method is a common method to measure the coal seam gas content (CSGC). However, cutting heat and friction heat will be generated in the core-tube coring process, which will increase the coal core temperature and the coal core gas loss, thus resulting in a large error in the determination of the gas content. The accuracy of the gas content determination is closely related to the temperature variation of coal core during core-taking. Based on this, the team developed the "thermal effect simulation device of coal core in the core-taking process" and carried out the temperature change test experiment of the coal core in the core-taking process under different conditions. The results show that the temperature variation of the coal core during the core-taking process shows four stages: constant temperature, rapid temperature rise, slow temperature rise, and temperature drop. The temperature rise rate, temperature rise duration, and temperature rise peak of the coal core increase with the increase in rotate speed, coal strength, friction area, and frictional load. In the axial direction, the closer to the upper end of the core pipe, the higher the core temperature. In the radial direction, the closer the core is to the wall of the core pipe, the higher the core temperature is. Under the influence of cutting heat and friction heat in the process of core-taking, the maximum heating rate of the core-taking tube wall within 8 min is 20 °C/min, the peak temperature is 158.4 °C, the average temperature of the wall is above 100 °C, and the average temperature rise of the coal core reaches 55.7 °C. Within 60 min, the average temperature of the coal core remained above 50 °C. The order of influence of coal core temperature from large to small is as follows: rotate speed, frictional load, friction area, and coal strength. It can provide a reference for accurately determining CSGC using the core-tube method or designing a coring device to eliminate or reduce the thermal effect during coring.