Study on the optimal dry ice dosage for coal seam freezing coring at different coring depths: experiment and modeling

• The temperature variation law of coring tubes at different depths was obtained. • The simulation revealed the temperature and heat variations of the coring tube. • The correlation between optimal freezing dose and coring depth was established. • The simulation confirmed the accuracy of calculating the optimal refrigerant dose. The key to applying freezing coring technology in measuring coal seam gas content lies in accurately estimating the refrigerant dosage. As coring depth increases, the heat generated by the coring tube rises, and accordingly, the required refrigerant dosage changes. To determine the optimal refrigerant dosage for freezing coring at different depths, this study used a self-developed coring simulation device to conduct simulated coring tests at various depths. The temperature variation characteristics of the coring tube at different depths were analyzed, and the heat generated during coring was calculated. Based on these results, the optimal refrigerant dosage was estimated, and a model was proposed for calculating the optimal dosage for freezing coring at different depths. The results show that as coring depth increases, the temperature of the coring tube rises gradually, while the rate of temperature increase slows down. Both the heat generated and dissipated by the coring tube increase with depth; the rate of heat generation slows gradually, while the rate of heat dissipation accelerates. At coring depths of 20 m, 40 m, 60 m, 100 m, and 140 m, the optimal refrigerant dosages were 1.26 kg, 1.52 kg, 1.69 kg, 2.01 kg, and 2.38 kg, respectively. A significant positive linear correlation was observed between refrigerant dosage and coring depth. Validated by numerical simulations, this model was confirmed to effectively estimate the optimal refrigerant dosage for freezing coring at different depths, providing theoretical guidance and references for the development and application of low-temperature freezing coring technology in coal seam gas content measurement.