Numerical Simulation Study on Supercritical Nitrogen Jet Flow Field

Conventional hydraulic fracturing technology faces problems such as high fracture initiation pressure and difficult packer setting in the stimulation of hot dry rock reservoirs. Supercritical nitrogen jet fracturing technology uses fluid pressure energy to coact with cold shock and is expected to achieve effective fracturing of hot dry rock reservoirs. In order to study the distribution law of supercritical nitrogen jet flow field, with the help of computational fluid mechanics method, after having considered the physical property variation of supercritical nitrogen, this paper figured out the velocity and pressure and temperature distribution of supercritical nitrogen jet flow field, conducted comparative analysis with liquid nitrogen jet, supercritical CO₂ jet and water jet flow fields, and simultaneously studied the flow field characteristics of supercritical nitrogen jet at different drawdowns, confining pressures and inlet temperatures. The study results show that compared with the other three jets, the supercritical nitrogen jet has the largest nozzle exit velocity and the longest potential core of jet; as the nozzle pressure drawdown increases and the supercritical nitrogen inlet temperature rises, the outlet velocity of fluid increases rapidly and the length of potential core increases; and the confining pressure has little effect on nozzle exit velocity, but the increase of confining pressure would lead to the decrease of potential core length. The study results provide theoretical guidance for the design of supercritical nitrogen jet fracturing stimulation parameters.