Study On Reasonable Freezing Dose In The Freezing Core Sampling Process

In order to study the reasonable dosage of refrigerant in the freezing core sampling process,this paper designed and developed a temperature measuring device for the coring tube coring process,collected and analyzed the temperature change data of the coring tube and coal core under different sampling depths.On this basis,the order sequential function specification method（SFSM）in the reverse heat transfer problem is used to invert the heat generation of the core tube wall,and the heat generation situation and heat generation of the core tube wall are obtained.Based on the relationship between coring depth and heat production in coring process of coring tube,the reasonable dose of freezing dose is calculated under the guidance of the first law of thermodynamics.The simulation experiment of Freezing Core Sampling was carried out to analyze the freezing effect of the freezing dose.The results of this paper are as follows:（1）The temperature change data of coring tube wall at 5m,20m and 40m coring depth were measured and recorded in real time by using an automatic temperature measuring device for coring tube.The maximum temperature of sensors arranged in coring tube wall reached 98.4 C.At the drill pipe propulsion stage,when the sampling depth was shallow（5 m,20 m）,the borehole deformation had little effect on the temperature of coring tube wall,but when the sampling depth was large（40 m）.The borehole deformation causes severe friction between the core tube wall and the hole wall,which makes the core tube temperature rise rapidly.（2）For different sampling depths,the temperature of the two sensors arranged in the core tube wall（expressed as T₁ and T₂）rises rapidly after cutting for a period of time,reaching the highest value at the end of cutting;the reason for the rapid rise of T₁and T₂ temperature in the cutting stage is the friction heat between the core tube and the coal wall,rather than the heat generated by the coal body at the bottom of the cutting hole of the bit.（3）The heating model of coring tube is established.The heat flux on the surface of coring tube wall is inverted by using SFSM combined with T₁ and T₂ data,and the heating curve of coring tube wall is drawn.According to the heat production curve,the temperature of two measuring points in the model was calculated,and the simulated values of T₁ and T₂ were obtained.The heat production curves were integrated by definite integral method,and the total heat production during coring at different sampling depths was obtained.The total heat production values were 1195790J,2667895J and 422650J at coring depths of 5m,20m and 40m.Combined with coring time at different coring depths,the average heat production power of coring at different coring depths was obtained.（4）The theoretical calculation of the required freezing dose was carried out,When the core depth is 5 m,20 m and 40 m,the reasonable dosage of refrigerant is2.03 kg,4.07 kg and 6.78 kg.The simulation experiment of freezing core sampling was carried out.The research showed the cooling amplitude of the coal core increased with the increase of the freezing dose under the same heating power,and the cooling speed of the coal core increased with the increase of the freezing dose.The freezing dose is constant,the average cooling speed of coal core increases with the increase of heating power.And they have compound linear correspondence.（5）According to the law of temperature change of coal core under different heating power obtained from the experiment,the refrigeration effect and temperature of coal core under actual heating power during coring process is analyzed,and compared with the field measurement of coal core temperature changes,it is proved that the refrigeration effect of coal core is good by using the reasonable freezing dose is calculated,and the temperature of coal core decreases greatly.