Study On Influencing Factors Of Coal Core Temperature Rise During Coring With Coring Tube

Coring with coring tube is a common sampling method for the determination of coal seam gas content in China.Cutting heat and friction heat will be generated in the process of coring with coring tube,which will lead to the temperature rise of coal core and increase the loss of coal core gas.In order to study the law of coal core temperature rise under different drilling parameters and coal seam conditions in the process of coring with coring tube,this paper studies the influencing factors of coal core temperature rise in the process of coring with coring tube based on the self-developed coal core thermal effect simulation device.Firstly,the simulation experiments of coal core temperature change under different coring speed,coal strength,friction pressure and friction area are carried out;Secondly,based on the relevant knowledge of actual coring process and heat transfer,combined with the measured temperature data of pipe wall and coal core,the coal core temperature rise model in the coring process is established by using numerical simulation software to explore the temporal and spatial distribution characteristics of coal core temperature field under different influencing factors;Finally,based on the average temperature rise data of coal core in numerical simulation,the significance of influencing factors of coal core temperature rise in coring process is discussed by using grey correlation theory.The main conclusions are as follows:(1)The thermal effect simulation device of coal core in coring process has been independently developed,which has the functions of real-time acquisition of core tube wall and coal core temperature,realizes the simulation of cutting heat and friction heat in the whole process of coring,and solves the problem of quantitative simulation test of core tube and coal core temperature under the conditions of different coal strength,friction area,rotating speed and friction pressure.(2)The temperature change characteristics of coal core under the quantitative change of influencing factors such as different rotating speed,coal strength,friction area and friction pressure during coring are studied.It is found that the change of coal core temperature presents four stages:delayed heating stage,rapid heating stage,slow heating stage and slow heat removal stage.The temperature rise rate,temperature rise duration and temperature rise peak value of coal core increase with the increase of rotating speed,coal strength,friction area and friction pressure.(3)The temperature rise model of coal core in coring process is established,and the temporal and spatial distribution characteristics of coal core temperature field in coring process are studied.The results show that under the influence of different rotating speeds,coal strength,friction area and friction pressure,the coal core temperature increases with the increase of the outer wall temperature of the coring tube.In the axial direction of the coal core,the closer it is to the upper end of the coring pipe,the higher the temperature is;In the radial direction,the closer to the core tube wall,the higher the coal core temperature.Temperature Th/d at each point inside the coal core.The relationship between Th/d and distance h/d and time t conforms to Poly2D function:Th/d=T0+ah+bt+ch2+dt2+f·h·t。(4)In the simulation experiment of coring stage,under the joint influence of cutting and friction,the maximum temperature rise rate of coring pipe wall is 0.34℃/s,the peak temperature is 158.4℃,the average temperature of pipe wall is more than 100℃,and the average temperature rise of coal core is 55.7℃.Within 60 min,the average temperature of coal core has been maintained above 50℃.(5)Based on the average temperature rise data of coal core in coring process under different influencing factors,the significance of influencing factors of coal core temperature rise is studied by using grey correlation theory,and the correlation degree of rotating speed,coal strength,friction area and friction pressure is calculated.The results show that these factors have a positive correlation on the temperature rise of coal core,and the order of influence is as follows:coring speed>friction pressure>friction area>coal strength.There are 38 figures,27 tables and 82 references.