Study On The Temperature Variation Characteristics Of Coal Core During Freezing Coring

Exploring the temperature variation characteristics of coal core during the process of freezing coring is very important for determining the gas desorption law and desorption capacity in variable temperature process.Firstly,this paper analyzes the influence of drilling parameters on the temperature of coring bit by establishing the temperature rise model of coring bit in coring process;secondly,the temperature change datas of coring tube wall in coring process is collected in real time by using the improved coring temperature acquisition device,so as to analyze the influence of drilling depths,drilling parameters and damage types on coring temperature;then,based on the similarity of simulation test,the freezing coring simulation test device is built.the simulation test of coal core temperature change in different core temperature,gas pressure and metamorphic degree is carried out during the process of freezing coring,and the change of coal core temperature field is simulated with numerical simulation software to obtain the distribution of coal core internal temperature field and the temporal and spatial characteristics during the process of freezing coring.The main conclusions are as follows:(1)Based on Jaeger’s infinite individual heat transfer model under instantaneous point heat source,the temperature rise model of core bit during coring is established,and the analytical relationship between the temperature rise of core bit and drilling parameters is derived.(2)In the coring process,the cutting speed and torque of drilling machine have great influence on the temperature rise of coring bit.The temperature rise of coring bit is proportional to cutting speed and torque;The highest cutting edge temperature of the coring bit occurs from the outside to the middle of the cutting edge.(3)Under the tectonically deformed coal seam and the same drilling parameters,the greater the drilling depth,the higher the wall temperature of coring tube;In the undeformed coal seam and the same drilling depth,the higher the cutting speed of the drill,the faster the wall temperature of coring tube will rise,and the greater the temperature rise range;the higher the cutting torque,the faster the wall temperature of coring tube will rise,but the temperature rise range is basically the same;under the same drilling parameters and drilling depth,the greater the degree of coal breakage,the lower the wall temperature rise of coring tube and the smaller the temperature rise range.(4)The coring temperature,gas pressure and metamorphic degree of coal core have significant effects on the temperature of coal core.When the gas pressure of coal core is constant,the cooling time of coal core increases with the increase of coring temperature,but the cooling speed and range decrease;when the coring temperature is fixed,the greater the gas pressure,the cooling time of coal core decreases,but the cooling speed and range increase;when the coring temperature and gas pressure of coal core are constant,the greater the degree of coal metamorphism,the smaller the cooling time of coal core,and the greater the cooling speed and range.(5)The Freezing Coring Technology has better effect on coal with gas than coal without gas,and has better effect on coal with high metamorphism than coal with low metamorphism;the cooling rate of coal core decreases gradually with the progress of freezing test;The difference of coal core edge temperature and medium temperature varies from large to small,and finally tends to 0.(6)During the freezing coring,the core temperature decreases in the form of exponential function under different coring temperature,which conforms to the equation T=a*0.999t+b;under different gas pressure of coal core,the change curve of coal core edge temperature conforms to the equation T=a+b*0.967t,the change curve of coal core medium temperature conforms to the equation T=a+b*0.983t;under different degrees of coal metamorphism,the temperature curve of long-flame coal conforms to the equation T=a+b*0.983t;the coking coal conforms to the equation T=a+b*0.979t,the meager-mean coal conforms to the equation T=a+b*0.978t,the anthracite coal conforms to the equation T=a+b*0.973t.(7)The simulation results of the heat conduction model established in this paper are reliable.Under the conditions of different coring temperature and gas pressure of coal core,when the core is frozen for 10min,there is obvious temperature difference inside and outside the coal core,the temperature in the middle of the coal core is the highest,the temperature in the outer wall is the lowest,and the radial temperature gradually decreases from the inside to the outside;when the coring is 150min,the temperature difference inside the coal core is small,and the temperature in the coal core is in a dynamic equilibrium state;with the extension of the test time,the temperature in the middle of the coal core and the temperature in the outer wall decrease in the form of exponential function,and the difference between them decreases gradually,the cooling rate of the outer wall of the coal core is much faster than that of the middle part;and the radial temperature curve of coal core basically showes quadratic function change when the core is frozen for 5min,10min and 50min,which conforms to the equation T=a*x2+b*x+c.