Study On Gas Desorption Law Of Coal Core In The Process Of Freezing Coring

In the process of freezing coring,the drill bit drilling coal wall causes the temperature of coal core to rise,and the coal core is affected by the refrigerant at the same time,which causes the temperature of coal core to change.The temperature is an important factor affecting the gas desorption,and the amount of gas desorption and loss will be affected.First of all,relying on the self-made core tube core process pipe wall temperature measurement device,collect the pipe wall temperature change data under the condition of different sampling depth,and on this basis,carry out the coal core gas desorption experiments under different coal core gas pressure,different sampling depth,different damage types and different metamorphic degrees through the low-temperature freezing core coal coring simulation test device The dynamic change and desorption characteristics of the system were studied.The conclusions are as follows:(1)The temperature change of the core tube wall in the real core taking process is mainly divided into four stages: constant temperature stage,slow temperature rising stage,fast rising stage and falling stage,which respectively correspond to the installation,drilling,drilling and stripping processes in the coring process;(2)In the process of freezing core extraction,the change of gas desorption of coal core can be divided into four stages: rapid increase stage,short-term stability stage,medium-term decrease stage and later stability stage.At the same coring depth,the greater the coal core pressure is,the greater the gas desorption capacity is,and the difference between the low pressure and high pressure desorption capacity is obvious;at the same coal core pressure,the greater the coring depth is,the greater the gas desorption capacity is;at the same coal core pressure and coring depth,the soft coal gas desorption capacity is greater than the hard coal desorption capacity;at the same coal core pressure and coring depth,the higher the metamorphic degree is,the greater the gas desorption capacity is;(3)In the process of freezing coring,the gas desorption rate of coal core can be divided into two stages: fast cooling stage and slow cooling stage.The time of fast attenuation stage is far less than that of slow attenuation stage.At the same coring depth,the greater the pressure of the coal core,the longer the time required for the gas desorption rate of the coal core to drop to 0ml /(g · min);at the same pressure of the coal core,the longer the time required for the gas desorption rate of the coal core to drop to 0ml /(g · min);at the same pressure and coring depth of the coal core,the gas desorption rate of the soft coal core to drop to 0 The time required for ml /(g · min)is longer than that for hard coal,the higher the metamorphic degree is,the longer the time required for the gas desorption rate of coal core to drop to 0 ml /(g · min)with the same core pressure and core depth;(4)Compared with the non freezing coring process,there is reverse suction in freezing coring process.At the same coring depth,the greater the core pressure is,the smaller the backdraft is;at the same core pressure,the greater the core depth is,the smaller the backdraft is,and the backdraft duration increases with the increase of the coring depth;at the same core pressure and coring depth,the gas backdraft of soft buried coal core is less than that of hard coal;at the same core pressure and coring depth,the higher the metamorphic degree is,the smaller the backdraft is.The change of suction velocity can be divided into two stages: rapid increase stage and slow attenuation stage.