NUMERICAL STUDY ON HEAT TRANSFER WITHIN A ROCK-AIR-WATER-ICE SYSTEM UNDER CRYOGENIC CONDITIONS

A numerical heat transfer model which couples heat conduction, natural convection, and the freezing process is built with ANSYS FLUENT. Then, 2D simulations of heat transfer in a rock-air-water-ice system under cryogenic conditions are conducted by using the model for studying the heat transfer mechanism in the reservoir stratum during cryogenic fracturing. The effects of air and water on the local temperature evolution are analyzed from the aspect of thermophysical properties, natural convection, and the water freezing process. For thermophysical properties, it is found that the influence of volumetric heat capacity is significant in the early stage of heat transfer, while in a long-term heat transfer process the effect of thermal conductivity is dominant. Natural convection alters the cold energy distribution and exerts different influences on the local temperature variation, and these effects could be weakened due to the presence of water. The release of latent heat due to water freezing delays the decrease of local temperature, while the newly formed ice phase accelerates the decrease of local temperature due to its relatively high thermal conductivity compared with that of water. Besides, the effect of water distribution on heat transfer is analyzed. Variation in water distribution alters the range and intensity of the impact brought by natural convection and water freezing, affecting temperature evolution. The combined effect of natural convection and water freezing affects the local temperature variation differently, depending on the time and position concerned.