Numerical analysis of characteristics of multi-orifice nozzle hydrothermal jet impact flow field and heat transfer

Hydrothermal jet technology is a new drilling method in which the rocks are broken by the combination of thermal spallation and high velocity impact effect. This technology uses a high temperature and high velocity jet to break rocks and has the potential to be more economically advantageous than conventional techniques for geothermal well drilling. Previous related studies primarily examine numerical simulation on one hydrothermal jet flow field, and to the best of our knowledge, no specific study addresses the thermo-physical interaction between wellbore fluid and ambient rock. This paper presents a multi-orifice nozzle model to investigate the features of a flow field with multiple hydrothermal jets and the heat transfer to ambient rocks. A transient impact flow field with multiple hydrothermal jets is analyzed in terms of axial temperature, bottomhole temperature, and bottomhole pressure. Also, downhole velocity field is specifically investigated. Next, influences of time, jet temperature, and jet pressure difference on the flow field and heat transfer between wellbore fluid and ambient rocks are predicted and compared. The results indicate that the bottomhole central temperature and pressure are higher than the two sides under multiple hydrothermal jets conditions, which is similar to the flow pattern with a single jet. Moreover, the distribution of axial velocity has three peaks at cross-sections, and the centerline axial velocity is the highest. There is a negative relationship between the maximum radial velocity and the ratio between axial distance and nozzle diameter (LSD). Also, the position of the maximum radial velocity moves to the side wall as the ratio (LID) increases. Second, the bottomhole temperature increases uniformly with increase in jet temperature. The bottomhole temperature becomes decreasingly sensitive to the variance of pressure difference, and the bottomhole pressure exhibits a ladder distribution. Finally, while an increase in either jet temperature or pressure difference can enhance the multiple hydrothermal jets heat transfer effect, increasing the jet temperature is considerably more effective. All of these results are beneficial to the parameters design for the hydrothermal jet drilling technology. (C) 2016 Elsevier B.V. All rights reserved.