NUMERICAL ANALYSIS OF FLOW TRANSPORT AND HEAT TRANSFER IN HDR DRILLING WITH HING-PRESSURE LIQUID NITROGEN JET
High-pressure liquid nitrogen jet technology is a novel drilling method, which is expected to be suitable for the exploitation of hot dry rock (HDR) resources, in which the rocks are broken coupled by thermal stresses and liquid impact. This paper presents a numerical analysis of flow transport and heat transfer in porous rock during HDR drilling with liquid nitrogen jet. The standard κ-ε model and Darcy-Brinkman-Forchheimer model are employed to calculate the fluid flow in fluid region and porous-rock region respectively. The heat transfer in porous rock is evaluate by the local thermal equilibrium model. In addition, the thermo-physical properties of liquid nitrogen and rock are considered. The effects of four key jet-parameters on rock heat transfer are analyzed in detail. The simulation results show that the high-pressure liquid impact promotes the seepage flow in porous rock, which can have a profound effect on heat transfer. Parametric analysis results indicate that the ambient pressure in bottom-hole and the initial liquid nitrogen temperature affect the heat transfer rate in rock significantly, while the parameters of nozzle's pressure drop and jet standoff distance have a slight influence on temperature distribution of porous rock. Results in this paper are of great significance to the parametric design of high-pressure liquid nitrogen jet drilling process.